From f699660479f4f2bedacf59d4a5203d7cc189e4a7 Mon Sep 17 00:00:00 2001
From: "Pedro J. Aramburu" <paramburu@gmail.com>
Date: Wed, 8 Apr 2026 16:05:58 -0300
Subject: [PATCH] Add exchange rate feature with multi-currency transactions
 and transfers support (#1099)

Co-authored-by: Pedro J. Aramburu <pedro@joakin.dev>
---
 app/components/DS/select.html.erb             |   3 +-
 app/components/UI/account/chart.rb            |   6 +-
 app/controllers/exchange_rates_controller.rb  |  36 +++
 app/controllers/reports_controller.rb         |  12 +-
 app/controllers/transactions_controller.rb    |  26 +-
 app/controllers/transfers_controller.rb       |  32 +-
 .../exchange_rate_form_controller.js          | 298 ++++++++++++++++++
 .../controllers/form_dropdown_controller.js   |   3 +
 .../transaction_form_controller.js            |  60 ++++
 .../controllers/transfer_form_controller.js   |  59 ++++
 app/models/balance/sync_cache.rb              |  15 +-
 app/models/holding/forward_calculator.rb      |   6 +-
 app/models/holding/portfolio_cache.rb         |   6 +-
 app/models/holding/reverse_calculator.rb      |   6 +-
 app/models/transaction.rb                     |  37 +++
 app/models/transfer/creator.rb                |  16 +-
 app/views/shared/_exchange_rate_tabs.html.erb |  39 +++
 app/views/shared/_money_field.html.erb        |  18 +-
 app/views/transactions/_form.html.erb         |  64 +++-
 app/views/transfers/_form.html.erb            |  50 ++-
 config/locales/views/shared/ca.yml            |   6 +
 config/locales/views/shared/de.yml            |   6 +
 config/locales/views/shared/en.yml            |   6 +
 config/locales/views/shared/es.yml            |   6 +
 config/locales/views/shared/fr.yml            |   6 +
 config/locales/views/shared/nb.yml            |  32 +-
 config/locales/views/shared/nl.yml            |   6 +
 config/locales/views/shared/pt-BR.yml         |   6 +
 config/locales/views/shared/ro.yml            |   6 +
 config/locales/views/shared/tr.yml            |   6 +
 config/locales/views/shared/zh-CN.yml         |   6 +
 config/locales/views/shared/zh-TW.yml         |   6 +
 config/locales/views/transfers/en.yml         |   8 +
 config/locales/views/transfers/es.yml         |   8 +
 config/routes.rb                              |   2 +
 lib/money.rb                                  |  20 +-
 test/application_system_test_case.rb          |  14 +
 .../exchange_rates_controller_test.rb         | 173 ++++++++++
 .../transactions_controller_test.rb           | 153 +++++++++
 test/controllers/transfers_controller_test.rb | 137 ++++++++
 test/lib/money_test.rb                        |  21 +-
 .../models/balance/forward_calculator_test.rb |  14 +-
 test/models/balance/sync_cache_test.rb        | 156 +++++++++
 test/models/holding_test.rb                   |   5 +-
 test/models/transaction_test.rb               |  60 ++++
 test/models/transfer/creator_test.rb          | 100 ++++++
 .../transactions_form_exchange_rate_test.rb   | 146 +++++++++
 test/system/transfers_test.rb                 |  52 +++
 48 files changed, 1886 insertions(+), 73 deletions(-)
 create mode 100644 app/controllers/exchange_rates_controller.rb
 create mode 100644 app/javascript/controllers/exchange_rate_form_controller.js
 create mode 100644 app/javascript/controllers/transaction_form_controller.js
 create mode 100644 app/javascript/controllers/transfer_form_controller.js
 create mode 100644 app/views/shared/_exchange_rate_tabs.html.erb
 create mode 100644 test/controllers/exchange_rates_controller_test.rb
 create mode 100644 test/models/balance/sync_cache_test.rb
 create mode 100644 test/system/transactions_form_exchange_rate_test.rb

diff --git a/app/components/DS/select.html.erb b/app/components/DS/select.html.erb
index 3ae5ce0a6..8f1ffe3e4 100644
--- a/app/components/DS/select.html.erb
+++ b/app/components/DS/select.html.erb
@@ -8,7 +8,8 @@
             value: @selected_value,
             data: {
               "form-dropdown-target": "input",
-              "auto-submit-target": "auto"
+              "auto-submit-target": "auto",
+              **(options.dig(:html_options, :data) || {})
             } %>
         <button type="button"
                 class="form-field__input w-full"
diff --git a/app/components/UI/account/chart.rb b/app/components/UI/account/chart.rb
index 61ae4d6fc..ee55e499a 100644
--- a/app/components/UI/account/chart.rb
+++ b/app/components/UI/account/chart.rb
@@ -55,7 +55,11 @@ class UI::Account::Chart < ApplicationComponent
   def converted_balance_money
     return nil unless foreign_currency?
 
-    account.balance_money.exchange_to(account.family.currency, fallback_rate: 1)
+    begin
+      account.balance_money.exchange_to(account.family.currency)
+    rescue Money::ConversionError
+      nil
+    end
   end
 
   def view
diff --git a/app/controllers/exchange_rates_controller.rb b/app/controllers/exchange_rates_controller.rb
new file mode 100644
index 000000000..78be651b4
--- /dev/null
+++ b/app/controllers/exchange_rates_controller.rb
@@ -0,0 +1,36 @@
+class ExchangeRatesController < ApplicationController
+  def show
+    # Pure currency-to-currency exchange rate lookup
+    unless params[:from].present? && params[:to].present?
+      return render json: { error: "from and to currencies are required" }, status: :bad_request
+    end
+
+    from_currency = params[:from].upcase
+    to_currency = params[:to].upcase
+
+    # Same currency returns 1.0
+    if from_currency == to_currency
+      return render json: { rate: 1.0, same_currency: true }
+    end
+
+    # Parse date
+    begin
+      date = params[:date].present? ? Date.parse(params[:date]) : Date.current
+    rescue ArgumentError, TypeError
+      return render json: { error: "Invalid date format" }, status: :bad_request
+    end
+
+    begin
+      rate_obj = ExchangeRate.find_or_fetch_rate(from: from_currency, to: to_currency, date: date)
+    rescue StandardError
+      return render json: { error: "Failed to fetch exchange rate" }, status: :bad_request
+    end
+
+    if rate_obj.nil?
+      return render json: { error: "Exchange rate not found" }, status: :not_found
+    end
+
+    rate_value = rate_obj.is_a?(Numeric) ? rate_obj : rate_obj.rate
+    render json: { rate: rate_value.to_f }
+  end
+end
diff --git a/app/controllers/reports_controller.rb b/app/controllers/reports_controller.rb
index 47202ec48..61d460c36 100644
--- a/app/controllers/reports_controller.rb
+++ b/app/controllers/reports_controller.rb
@@ -388,7 +388,11 @@ class ReportsController < ApplicationController
       # Helper to process an entry (transaction or trade)
       process_entry = ->(category, entry, is_trade) do
         type = entry.amount > 0 ? "expense" : "income"
-        converted_amount = Money.new(entry.amount.abs, entry.currency).exchange_to(family_currency, fallback_rate: 1).amount
+        begin
+          converted_amount = Money.new(entry.amount.abs, entry.currency).exchange_to(family_currency).amount
+        rescue Money::ConversionError
+          converted_amount = entry.amount.abs
+        end
 
         if category.nil?
           # Uncategorized or Other Investments (for trades)
@@ -679,7 +683,11 @@ class ReportsController < ApplicationController
         month_key = entry.date.beginning_of_month
 
         # Convert to family currency
-        converted_amount = Money.new(entry.amount.abs, entry.currency).exchange_to(family_currency, fallback_rate: 1).amount
+        begin
+          converted_amount = Money.new(entry.amount.abs, entry.currency).exchange_to(family_currency).amount
+        rescue Money::ConversionError
+          converted_amount = entry.amount.abs
+        end
 
         key = [ category_name, type ]
         breakdown[key] ||= { category: category_name, type: type, months: {}, total: 0 }
diff --git a/app/controllers/transactions_controller.rb b/app/controllers/transactions_controller.rb
index 6548d26ed..c70e606bb 100644
--- a/app/controllers/transactions_controller.rb
+++ b/app/controllers/transactions_controller.rb
@@ -353,6 +353,30 @@ class TransactionsController < ApplicationController
     head :unprocessable_entity
   end
 
+  def exchange_rate
+    account = Current.family.accounts.find(params[:account_id])
+    currency_from = params[:currency]
+    date = params[:date]&.to_date || Date.current
+
+    if account.currency == currency_from
+      render json: { same_currency: true, rate: 1.0 }
+    else
+      rate_obj = ExchangeRate.find_or_fetch_rate(
+        from: currency_from,
+        to: account.currency,
+        date: date
+      )
+
+      if rate_obj.nil?
+        return render json: { error: "Exchange rate not found" }, status: :not_found
+      end
+
+      rate_value = rate_obj.is_a?(Numeric) ? rate_obj : rate_obj.rate
+
+      render json: { rate: rate_value.to_f, account_currency: account.currency }
+    end
+  end
+
   private
     def accessible_transactions
       Current.family.transactions
@@ -409,7 +433,7 @@ class TransactionsController < ApplicationController
     def entry_params
       entry_params = params.require(:entry).permit(
         :name, :date, :amount, :currency, :excluded, :notes, :nature, :entryable_type,
-        entryable_attributes: [ :id, :category_id, :merchant_id, :kind, :investment_activity_label, { tag_ids: [] } ]
+        entryable_attributes: [ :id, :category_id, :merchant_id, :kind, :investment_activity_label, :exchange_rate, { tag_ids: [] } ]
       )
 
       nature = entry_params.delete(:nature)
diff --git a/app/controllers/transfers_controller.rb b/app/controllers/transfers_controller.rb
index 0a000fad6..cdd9ce01c 100644
--- a/app/controllers/transfers_controller.rb
+++ b/app/controllers/transfers_controller.rb
@@ -2,17 +2,11 @@ class TransfersController < ApplicationController
   include StreamExtensions
 
   before_action :set_transfer, only: %i[show destroy update]
+  before_action :set_accounts, only: %i[new create]
 
   def new
     @transfer = Transfer.new
     @from_account_id = params[:from_account_id]
-
-    @accounts = accessible_accounts
-    .alphabetically
-    .includes(
-      :account_providers,
-      logo_attachment: :blob
-    )
   end
 
   def show
@@ -31,8 +25,9 @@ class TransfersController < ApplicationController
       family: Current.family,
       source_account_id: source_account.id,
       destination_account_id: destination_account.id,
-      date: Date.parse(transfer_params[:date]),
-      amount: transfer_params[:amount].to_d
+      date: transfer_params[:date].present? ? Date.parse(transfer_params[:date]) : Date.current,
+      amount: transfer_params[:amount].to_d,
+      exchange_rate: transfer_params[:exchange_rate].presence&.to_d
     ).create
 
     if @transfer.persisted?
@@ -45,6 +40,14 @@ class TransfersController < ApplicationController
       @from_account_id = transfer_params[:from_account_id]
       render :new, status: :unprocessable_entity
     end
+  rescue Money::ConversionError
+    @transfer ||= Transfer.new
+    @transfer.errors.add(:base, "Exchange rate unavailable for selected currencies and date")
+    render :new, status: :unprocessable_entity
+  rescue ArgumentError
+    @transfer ||= Transfer.new
+    @transfer.errors.add(:date, "is invalid")
+    render :new, status: :unprocessable_entity
   end
 
   def update
@@ -85,7 +88,16 @@ class TransfersController < ApplicationController
     end
 
     def transfer_params
-      params.require(:transfer).permit(:from_account_id, :to_account_id, :amount, :date, :name, :excluded)
+      params.require(:transfer).permit(:from_account_id, :to_account_id, :amount, :date, :name, :excluded, :exchange_rate)
+    end
+
+    def set_accounts
+      @accounts = accessible_accounts
+        .alphabetically
+        .includes(
+          :account_providers,
+          logo_attachment: :blob
+        )
     end
 
     def transfer_update_params
diff --git a/app/javascript/controllers/exchange_rate_form_controller.js b/app/javascript/controllers/exchange_rate_form_controller.js
new file mode 100644
index 000000000..80126bb20
--- /dev/null
+++ b/app/javascript/controllers/exchange_rate_form_controller.js
@@ -0,0 +1,298 @@
+import { Controller } from "@hotwired/stimulus";
+
+export default class extends Controller {
+  static targets = [
+    "amount",
+    "destinationAmount",
+    "date",
+    "exchangeRateContainer",
+    "exchangeRateField",
+    "convertDestinationDisplay",
+    "calculateRateDisplay"
+  ];
+
+  static values = {
+    exchangeRateUrl: String,
+    accountCurrencies: Object
+  };
+
+  connect() {
+    this.sourceCurrency = null;
+    this.destinationCurrency = null;
+    this.activeTab = "convert";
+
+    if (!this.hasRequiredExchangeRateTargets()) {
+      return;
+    }
+
+    this.checkCurrencyDifference();
+  }
+
+  hasRequiredExchangeRateTargets() {
+    return this.hasDateTarget;
+  }
+
+  checkCurrencyDifference() {
+    const context = this.getExchangeRateContext();
+
+    if (!context) {
+      this.hideExchangeRateField();
+      return;
+    }
+
+    const { fromCurrency, toCurrency, date } = context;
+
+    if (!fromCurrency || !toCurrency) {
+      this.hideExchangeRateField();
+      return;
+    }
+
+    this.sourceCurrency = fromCurrency;
+    this.destinationCurrency = toCurrency;
+
+    if (fromCurrency === toCurrency) {
+      this.hideExchangeRateField();
+      return;
+    }
+
+    this.fetchExchangeRate(fromCurrency, toCurrency, date);
+  }
+
+  onExchangeRateTabClick(event) {
+    const btn = event.target.closest("button[data-id]");
+    if (!btn) {
+      return;
+    }
+
+    const nextTab = btn.dataset.id;
+
+    if (nextTab === this.activeTab) {
+      return;
+    }
+
+    this.activeTab = nextTab;
+
+    if (this.activeTab === "convert") {
+      this.clearCalculateRateFields();
+    } else if (this.activeTab === "calculateRate") {
+      this.clearConvertFields();
+    }
+  }
+
+  onAmountChange() {
+    this.onAmountInputChange();
+  }
+
+  onSourceAmountChange() {
+    this.onAmountInputChange();
+  }
+
+  onAmountInputChange() {
+    if (!this.hasAmountTarget) {
+      return;
+    }
+
+    if (this.activeTab === "convert") {
+      this.calculateConvertDestination();
+    } else {
+      this.calculateRateFromAmounts();
+    }
+  }
+
+  onConvertSourceAmountChange() {
+    this.calculateConvertDestination();
+  }
+
+  onConvertExchangeRateChange() {
+    this.calculateConvertDestination();
+  }
+
+  calculateConvertDestination() {
+    if (!this.hasAmountTarget || !this.hasExchangeRateFieldTarget || !this.hasConvertDestinationDisplayTarget) {
+      return;
+    }
+
+    const amount = Number.parseFloat(this.amountTarget.value);
+    const rate = Number.parseFloat(this.exchangeRateFieldTarget.value);
+
+    if (amount && rate && rate !== 0) {
+      const destAmount = (amount * rate).toFixed(2);
+      this.convertDestinationDisplayTarget.textContent = this.destinationCurrency ? `${destAmount} ${this.destinationCurrency}` : destAmount;
+    } else {
+      this.convertDestinationDisplayTarget.textContent = "-";
+    }
+  }
+
+  onCalculateRateSourceAmountChange() {
+    this.calculateRateFromAmounts();
+  }
+
+  onCalculateRateDestinationAmountChange() {
+    this.calculateRateFromAmounts();
+  }
+
+  calculateRateFromAmounts() {
+    if (!this.hasAmountTarget || !this.hasDestinationAmountTarget || !this.hasCalculateRateDisplayTarget || !this.hasExchangeRateFieldTarget) {
+      return;
+    }
+
+    const amount = Number.parseFloat(this.amountTarget.value);
+    const destAmount = Number.parseFloat(this.destinationAmountTarget.value);
+
+    if (amount && destAmount && amount !== 0) {
+      const rate = destAmount / amount;
+      const formattedRate = this.formatExchangeRate(rate);
+      this.calculateRateDisplayTarget.textContent = formattedRate;
+      this.exchangeRateFieldTarget.value = rate.toFixed(14);
+    } else {
+      this.calculateRateDisplayTarget.textContent = "-";
+      this.exchangeRateFieldTarget.value = "";
+    }
+  }
+
+  formatExchangeRate(rate) {
+    let formattedRate = rate.toFixed(14);
+    formattedRate = formattedRate.replace(/(\.\d{2}\d*?)0+$/, "$1");
+
+    if (!formattedRate.includes(".")) {
+      formattedRate += ".00";
+    } else if (formattedRate.match(/\.\d$/)) {
+      formattedRate += "0";
+    }
+
+    return formattedRate;
+  }
+
+  clearConvertFields() {
+    if (this.hasExchangeRateFieldTarget) {
+      this.exchangeRateFieldTarget.value = "";
+    }
+    if (this.hasConvertDestinationDisplayTarget) {
+      this.convertDestinationDisplayTarget.textContent = "-";
+    }
+  }
+
+  clearCalculateRateFields() {
+    if (this.hasDestinationAmountTarget) {
+      this.destinationAmountTarget.value = "";
+    }
+    if (this.hasCalculateRateDisplayTarget) {
+      this.calculateRateDisplayTarget.textContent = "-";
+    }
+    if (this.hasExchangeRateFieldTarget) {
+      this.exchangeRateFieldTarget.value = "";
+    }
+  }
+
+  async fetchExchangeRate(fromCurrency, toCurrency, date) {
+    if (this.exchangeRateAbortController) {
+      this.exchangeRateAbortController.abort();
+    }
+
+    this.exchangeRateAbortController = new AbortController();
+    const signal = this.exchangeRateAbortController.signal;
+
+    try {
+      const url = new URL(this.exchangeRateUrlValue, window.location.origin);
+      url.searchParams.set("from", fromCurrency);
+      url.searchParams.set("to", toCurrency);
+      if (date) {
+        url.searchParams.set("date", date);
+      }
+
+      const response = await fetch(url, { signal });
+      const data = await response.json();
+
+      if (!this.isCurrentExchangeRateState(fromCurrency, toCurrency, date)) {
+        return;
+      }
+
+      if (!response.ok) {
+        if (this.shouldShowManualExchangeRate(data)) {
+          this.showManualExchangeRateField();
+        } else {
+          this.hideExchangeRateField();
+        }
+        return;
+      }
+
+      if (data.same_currency) {
+        this.hideExchangeRateField();
+      } else {
+        this.sourceCurrency = fromCurrency;
+        this.destinationCurrency = toCurrency;
+        this.showExchangeRateField(data.rate);
+      }
+    } catch (error) {
+      if (error.name === "AbortError") {
+        return;
+      }
+
+      console.error("Error fetching exchange rate:", error);
+      this.hideExchangeRateField();
+    }
+  }
+
+  showExchangeRateField(rate) {
+    if (this.hasExchangeRateFieldTarget) {
+      this.exchangeRateFieldTarget.value = this.formatExchangeRate(rate);
+    }
+    if (this.hasExchangeRateContainerTarget) {
+      this.exchangeRateContainerTarget.classList.remove("hidden");
+    }
+
+    this.calculateConvertDestination();
+  }
+
+  showManualExchangeRateField() {
+    const context = this.getExchangeRateContext();
+    this.sourceCurrency = context?.fromCurrency || null;
+    this.destinationCurrency = context?.toCurrency || null;
+
+    if (this.hasExchangeRateFieldTarget) {
+      this.exchangeRateFieldTarget.value = "";
+    }
+    if (this.hasExchangeRateContainerTarget) {
+      this.exchangeRateContainerTarget.classList.remove("hidden");
+    }
+
+    this.calculateConvertDestination();
+  }
+
+  shouldShowManualExchangeRate(data) {
+    if (!data || typeof data.error !== "string") {
+      return false;
+    }
+
+    return data.error === "Exchange rate not found" || data.error === "Exchange rate unavailable";
+  }
+
+  hideExchangeRateField() {
+    if (this.hasExchangeRateContainerTarget) {
+      this.exchangeRateContainerTarget.classList.add("hidden");
+    }
+    if (this.hasExchangeRateFieldTarget) {
+      this.exchangeRateFieldTarget.value = "";
+    }
+    if (this.hasConvertDestinationDisplayTarget) {
+      this.convertDestinationDisplayTarget.textContent = "-";
+    }
+    if (this.hasCalculateRateDisplayTarget) {
+      this.calculateRateDisplayTarget.textContent = "-";
+    }
+    if (this.hasDestinationAmountTarget) {
+      this.destinationAmountTarget.value = "";
+    }
+
+    this.sourceCurrency = null;
+    this.destinationCurrency = null;
+  }
+
+  getExchangeRateContext() {
+    throw new Error("Subclasses must implement getExchangeRateContext()");
+  }
+
+  isCurrentExchangeRateState(_fromCurrency, _toCurrency, _date) {
+    throw new Error("Subclasses must implement isCurrentExchangeRateState()");
+  }
+}
diff --git a/app/javascript/controllers/form_dropdown_controller.js b/app/javascript/controllers/form_dropdown_controller.js
index d191106f8..a13f22eef 100644
--- a/app/javascript/controllers/form_dropdown_controller.js
+++ b/app/javascript/controllers/form_dropdown_controller.js
@@ -9,6 +9,9 @@ export default class extends Controller {
     const inputEvent = new Event("input", { bubbles: true })
     this.inputTarget.dispatchEvent(inputEvent)
 
+    const changeEvent = new Event("change", { bubbles: true })
+    this.inputTarget.dispatchEvent(changeEvent)
+
     const form = this.element.closest("form")
     const controllers = (form?.dataset.controller || "").split(/\s+/)
     if (form && controllers.includes("auto-submit-form")) {
diff --git a/app/javascript/controllers/transaction_form_controller.js b/app/javascript/controllers/transaction_form_controller.js
new file mode 100644
index 000000000..739b923da
--- /dev/null
+++ b/app/javascript/controllers/transaction_form_controller.js
@@ -0,0 +1,60 @@
+import ExchangeRateFormController from "controllers/exchange_rate_form_controller";
+
+// Connects to data-controller="transaction-form"
+export default class extends ExchangeRateFormController {
+  static targets = [
+    ...ExchangeRateFormController.targets,
+    "account",
+    "currency"
+  ];
+
+  hasRequiredExchangeRateTargets() {
+    if (!this.hasAccountTarget || !this.hasCurrencyTarget || !this.hasDateTarget) {
+      return false;
+    }
+
+    return true;
+  }
+
+  getExchangeRateContext() {
+    if (!this.hasRequiredExchangeRateTargets()) {
+      return null;
+    }
+
+    const accountId = this.accountTarget.value;
+    const currency = this.currencyTarget.value;
+    const date = this.dateTarget.value;
+
+    if (!accountId || !currency) {
+      return null;
+    }
+
+    const accountCurrency = this.accountCurrenciesValue[accountId];
+    if (!accountCurrency) {
+      return null;
+    }
+
+    return {
+      fromCurrency: currency,
+      toCurrency: accountCurrency,
+      date
+    };
+  }
+
+  isCurrentExchangeRateState(fromCurrency, toCurrency, date) {
+    if (!this.hasRequiredExchangeRateTargets()) {
+      return false;
+    }
+
+    const currentAccountId = this.accountTarget.value;
+    const currentCurrency = this.currencyTarget.value;
+    const currentDate = this.dateTarget.value;
+    const currentAccountCurrency = this.accountCurrenciesValue[currentAccountId];
+
+    return fromCurrency === currentCurrency && toCurrency === currentAccountCurrency && date === currentDate;
+  }
+
+  onCurrencyChange() {
+    this.checkCurrencyDifference();
+  }
+}
diff --git a/app/javascript/controllers/transfer_form_controller.js b/app/javascript/controllers/transfer_form_controller.js
new file mode 100644
index 000000000..e8d17437c
--- /dev/null
+++ b/app/javascript/controllers/transfer_form_controller.js
@@ -0,0 +1,59 @@
+import ExchangeRateFormController from "controllers/exchange_rate_form_controller";
+
+// Connects to data-controller="transfer-form"
+export default class extends ExchangeRateFormController {
+  static targets = [
+    ...ExchangeRateFormController.targets,
+    "fromAccount",
+    "toAccount"
+  ];
+
+  hasRequiredExchangeRateTargets() {
+    if (!this.hasFromAccountTarget || !this.hasToAccountTarget || !this.hasDateTarget) {
+      return false;
+    }
+
+    return true;
+  }
+
+  getExchangeRateContext() {
+    if (!this.hasRequiredExchangeRateTargets()) {
+      return null;
+    }
+
+    const fromAccountId = this.fromAccountTarget.value;
+    const toAccountId = this.toAccountTarget.value;
+    const date = this.dateTarget.value;
+
+    if (!fromAccountId || !toAccountId) {
+      return null;
+    }
+
+    const fromCurrency = this.accountCurrenciesValue[fromAccountId];
+    const toCurrency = this.accountCurrenciesValue[toAccountId];
+
+    if (!fromCurrency || !toCurrency) {
+      return null;
+    }
+
+    return {
+      fromCurrency,
+      toCurrency,
+      date
+    };
+  }
+
+  isCurrentExchangeRateState(fromCurrency, toCurrency, date) {
+    if (!this.hasRequiredExchangeRateTargets()) {
+      return false;
+    }
+
+    const currentFromAccountId = this.fromAccountTarget.value;
+    const currentToAccountId = this.toAccountTarget.value;
+    const currentFromCurrency = this.accountCurrenciesValue[currentFromAccountId];
+    const currentToCurrency = this.accountCurrenciesValue[currentToAccountId];
+    const currentDate = this.dateTarget.value;
+
+    return fromCurrency === currentFromCurrency && toCurrency === currentToCurrency && date === currentDate;
+  }
+}
diff --git a/app/models/balance/sync_cache.rb b/app/models/balance/sync_cache.rb
index a6e12c9ee..582774c38 100644
--- a/app/models/balance/sync_cache.rb
+++ b/app/models/balance/sync_cache.rb
@@ -27,13 +27,21 @@ class Balance::SyncCache
     end
 
     def converted_entries
-      @converted_entries ||= account.entries.excluding_split_parents.order(:date).to_a.map do |e|
+      @converted_entries ||= account.entries.excluding_split_parents.includes(:entryable).order(:date).to_a.map do |e|
         converted_entry = e.dup
+
+        # Extract custom exchange rate if present on Transaction
+        custom_rate = if e.entryable.is_a?(Transaction)
+          e.entryable.extra&.dig("exchange_rate")
+        end
+
+        # Use Money#exchange_to with custom rate if available, standard lookup otherwise
         converted_entry.amount = converted_entry.amount_money.exchange_to(
           account.currency,
           date: e.date,
-          fallback_rate: 1
+          custom_rate: custom_rate
         ).amount
+
         converted_entry.currency = account.currency
         converted_entry
       end
@@ -44,8 +52,7 @@ class Balance::SyncCache
         converted_holding = h.dup
         converted_holding.amount = converted_holding.amount_money.exchange_to(
           account.currency,
-          date: h.date,
-          fallback_rate: 1
+          date: h.date
         ).amount
         converted_holding.currency = account.currency
         converted_holding
diff --git a/app/models/holding/forward_calculator.rb b/app/models/holding/forward_calculator.rb
index ecb59e826..e231fb33c 100644
--- a/app/models/holding/forward_calculator.rb
+++ b/app/models/holding/forward_calculator.rb
@@ -89,7 +89,11 @@ class Holding::ForwardCalculator
 
         # Convert trade price to account currency if needed
         trade_price = Money.new(trade.price, trade.currency)
-        converted_price = trade_price.exchange_to(account.currency, fallback_rate: 1).amount
+        begin
+          converted_price = trade_price.exchange_to(account.currency).amount
+        rescue Money::ConversionError
+          converted_price = trade.price
+        end
 
         tracker[:total_cost] += converted_price * trade.qty
         tracker[:total_qty] += trade.qty
diff --git a/app/models/holding/portfolio_cache.rb b/app/models/holding/portfolio_cache.rb
index 6763d1fd1..eaca58309 100644
--- a/app/models/holding/portfolio_cache.rb
+++ b/app/models/holding/portfolio_cache.rb
@@ -36,7 +36,11 @@ class Holding::PortfolioCache
 
     price_money = Money.new(price.price, price.currency)
 
-    converted_amount = price_money.exchange_to(account.currency, fallback_rate: 1).amount
+    begin
+      converted_amount = price_money.exchange_to(account.currency).amount
+    rescue Money::ConversionError
+      converted_amount = price.price
+    end
 
     Security::Price.new(
       security_id: security_id,
diff --git a/app/models/holding/reverse_calculator.rb b/app/models/holding/reverse_calculator.rb
index d9ed2efe0..aeb0f256b 100644
--- a/app/models/holding/reverse_calculator.rb
+++ b/app/models/holding/reverse_calculator.rb
@@ -97,7 +97,11 @@ class Holding::ReverseCalculator
           if trade.qty > 0 # Only track buys
             security_id = trade.security_id
             trade_price = Money.new(trade.price, trade.currency)
-            converted_price = trade_price.exchange_to(account.currency, fallback_rate: 1).amount
+            begin
+              converted_price = trade_price.exchange_to(account.currency).amount
+            rescue Money::ConversionError
+              converted_price = trade.price
+            end
 
             tracker[security_id][:total_cost] += converted_price * trade.qty
             tracker[security_id][:total_qty] += trade.qty
diff --git a/app/models/transaction.rb b/app/models/transaction.rb
index 75e36bbdc..aeba12276 100644
--- a/app/models/transaction.rb
+++ b/app/models/transaction.rb
@@ -28,6 +28,43 @@ class Transaction < ApplicationRecord
 
   after_save :clear_merchant_unlinked_association, if: :merchant_id_previously_changed?
 
+  # Accessors for exchange_rate stored in extra jsonb field
+  def exchange_rate
+    extra&.dig("exchange_rate")
+  end
+
+  def exchange_rate=(value)
+    if value.blank?
+      self.extra = (extra || {}).merge("exchange_rate" => nil)
+    else
+      begin
+        normalized_value = Float(value)
+        self.extra = (extra || {}).merge("exchange_rate" => normalized_value)
+      rescue ArgumentError, TypeError
+        # Store the raw value for validation error reporting
+        self.extra = (extra || {}).merge("exchange_rate" => value, "exchange_rate_invalid" => true)
+      end
+    end
+  end
+
+  validate :exchange_rate_must_be_valid
+
+  private
+
+    def exchange_rate_must_be_valid
+      if extra&.dig("exchange_rate_invalid")
+        errors.add(:exchange_rate, "must be a number")
+      elsif exchange_rate.present?
+        # Convert to float for comparison
+        numeric_rate = exchange_rate.to_d rescue nil
+        if numeric_rate.nil? || numeric_rate <= 0
+          errors.add(:exchange_rate, "must be greater than 0")
+        end
+      end
+    end
+
+  public
+
   enum :kind, {
     standard: "standard", # A regular transaction, included in budget analytics
     funds_movement: "funds_movement", # Movement of funds between accounts, excluded from budget analytics
diff --git a/app/models/transfer/creator.rb b/app/models/transfer/creator.rb
index 1825e92d0..7aa8bc72c 100644
--- a/app/models/transfer/creator.rb
+++ b/app/models/transfer/creator.rb
@@ -1,10 +1,18 @@
 class Transfer::Creator
-  def initialize(family:, source_account_id:, destination_account_id:, date:, amount:)
+  def initialize(family:, source_account_id:, destination_account_id:, date:, amount:, exchange_rate: nil)
     @family = family
     @source_account = family.accounts.find(source_account_id) # early throw if not found
     @destination_account = family.accounts.find(destination_account_id) # early throw if not found
     @date = date
     @amount = amount.to_d
+
+    if exchange_rate.present?
+      rate_value = exchange_rate.to_d
+      raise ArgumentError, "exchange_rate must be greater than 0" unless rate_value > 0
+      @exchange_rate = rate_value
+    else
+      @exchange_rate = nil
+    end
   end
 
   def create
@@ -23,7 +31,7 @@ class Transfer::Creator
   end
 
   private
-    attr_reader :family, :source_account, :destination_account, :date, :amount
+    attr_reader :family, :source_account, :destination_account, :date, :amount, :exchange_rate
 
     def outflow_transaction
       name = "#{name_prefix} to #{destination_account.name}"
@@ -62,13 +70,13 @@ class Transfer::Creator
     end
 
     # If destination account has different currency, its transaction should show up as converted
-    # Future improvement: instead of a 1:1 conversion fallback, add a UI/UX flow for missing rates
+    # Uses user-provided exchange rate if available, otherwise requires a provider rate
     def inflow_converted_money
       Money.new(amount.abs, source_account.currency)
            .exchange_to(
              destination_account.currency,
              date: date,
-             fallback_rate: 1.0
+             custom_rate: exchange_rate
            )
     end
 
diff --git a/app/views/shared/_exchange_rate_tabs.html.erb b/app/views/shared/_exchange_rate_tabs.html.erb
new file mode 100644
index 000000000..1ba15d706
--- /dev/null
+++ b/app/views/shared/_exchange_rate_tabs.html.erb
@@ -0,0 +1,39 @@
+<%# locals: (controller_id:, controller_key:, help_text:, convert_tab_label:, calculate_rate_tab_label:, destination_amount_label:, exchange_rate_label:, convert_input:, destination_input:) %>
+
+<div class="hidden px-1 pt-2" data-action="click-><%= controller_id %>#onExchangeRateTabClick" data-<%= controller_id %>-target="exchangeRateContainer">
+  <p class="text-xs text-secondary mb-2"><%= help_text %></p>
+
+  <%= render DS::Tabs.new(active_tab: "convert") do |tabs| %>
+    <%= tabs.with_nav do |nav| %>
+      <%= nav.with_btn(id: "convert", label: convert_tab_label) %>
+      <%= nav.with_btn(id: "calculateRate", label: calculate_rate_tab_label) %>
+    <% end %>
+
+    <%= tabs.with_panel(tab_id: "convert") do %>
+      <div class="space-y-2 mb-3">
+        <%= convert_input %>
+
+        <div class="flex items-center justify-between p-2 bg-container-inset rounded text-sm">
+          <span class="text-secondary"><%= destination_amount_label %></span>
+          <span class="font-medium text-primary" data-<%= controller_id %>-target="convertDestinationDisplay">-</span>
+        </div>
+      </div>
+    <% end %>
+
+    <%= tabs.with_panel(tab_id: "calculateRate") do %>
+      <div class="space-y-2 mb-3">
+        <div class="form-field">
+          <div class="form-field__body">
+            <label class="form-field__label" for="<%= "#{controller_key}_destination_amount" %>"><%= destination_amount_label %></label>
+            <%= destination_input %>
+          </div>
+        </div>
+
+        <div class="flex items-center justify-between p-2 bg-container-inset rounded text-sm">
+          <span class="text-secondary"><%= exchange_rate_label %></span>
+          <span class="font-medium text-primary" data-<%= controller_id %>-target="calculateRateDisplay">-</span>
+        </div>
+      </div>
+    <% end %>
+  <% end %>
+</div>
diff --git a/app/views/shared/_money_field.html.erb b/app/views/shared/_money_field.html.erb
index 41776c28f..8ef25151f 100644
--- a/app/views/shared/_money_field.html.erb
+++ b/app/views/shared/_money_field.html.erb
@@ -60,26 +60,30 @@
           max: options[:max] || 99999999999999,
           step: options[:step] || currency.step,
           disabled: options[:disabled],
-          data: {
+          data: (options[:amount_data] || {}).merge({
             "money-field-target": "amount",
             "auto-submit-form-target": ("auto" if options[:auto_submit])
-          }.compact,
+          }.compact),
           required: options[:required] %>
       </div>
 
       <% unless options[:hide_currency] %>
         <div>
+          <% currency_data = (options[:currency_data] || {}).merge({
+               "money-field-target": "currency",
+               "auto-submit-form-target": ("auto" if options[:auto_submit])
+             }.compact)
+             # Preserve any existing action and append money-field handler
+             existing_action = currency_data.delete("action")
+             currency_data["action"] = ["change->money-field#handleCurrencyChange", existing_action].compact.join(" ")
+          %>
           <%= form.select currency_method,
                         Money::Currency.as_options.map(&:iso_code),
                         { inline: true, selected: currency.iso_code },
                         {
                           class: "w-fit pr-5 disabled:text-subdued form-field__input",
                           disabled: options[:disable_currency],
-                          data: {
-                            "money-field-target": "currency",
-                            action: "change->money-field#handleCurrencyChange",
-                            "auto-submit-form-target": ("auto" if options[:auto_submit])
-                          }.compact
+                          data: currency_data
                         } %>
         </div>
       <% end %>
diff --git a/app/views/transactions/_form.html.erb b/app/views/transactions/_form.html.erb
index 2ff28e05e..947f5444f 100644
--- a/app/views/transactions/_form.html.erb
+++ b/app/views/transactions/_form.html.erb
@@ -1,6 +1,7 @@
 <%# locals: (entry:, categories:) %>
 
-<%= styled_form_with model: entry, url: transactions_path, class: "space-y-4" do |f| %>
+<% account_currencies = Current.family.accounts.map { |a| [a.id, a.currency] }.to_h.to_json %>
+<%= styled_form_with model: entry, url: transactions_path, class: "space-y-4", data: { controller: "transaction-form", transaction_form_exchange_rate_url_value: exchange_rate_path, transaction_form_account_currencies_value: account_currencies } do |f| %>
   <% if entry.errors.any? %>
     <%= render "shared/form_errors", model: entry %>
   <% end %>
@@ -16,16 +17,69 @@
     <%= f.text_field :name, label: t(".description"), placeholder: t(".description_placeholder"), required: true %>
 
     <% if @entry.account_id %>
-      <%= f.hidden_field :account_id %>
+      <%= f.hidden_field :account_id, data: { transaction_form_target: "account" } %>
     <% else %>
-      <%= f.collection_select :account_id, accessible_accounts.manual.active.alphabetically, :id, :name, { prompt: t(".account_prompt"), label: t(".account"), selected: Current.user.default_account_for_transactions&.id, variant: :logo }, required: true, class: "form-field__input text-ellipsis" %>
+      <%= f.collection_select :account_id, accessible_accounts.manual.active.alphabetically, :id, :name, { prompt: t(".account_prompt"), label: t(".account"), selected: Current.user.default_account_for_transactions&.id, variant: :logo }, required: true, class: "form-field__input text-ellipsis", data: { transaction_form_target: "account", action: "change->transaction-form#checkCurrencyDifference" } %>
     <% end %>
 
-    <%= f.money_field :amount, label: t(".amount"), required: true %>
+    <%= f.money_field :amount, 
+      label: t(".amount"), 
+      required: true,
+      container_class: "money-field-wrapper",
+      amount_data: { transaction_form_target: "amount", action: "input->transaction-form#onAmountChange" },
+      currency_data: { transaction_form_target: "currency", action: "change->transaction-form#onCurrencyChange" } %>
+      
     <%= f.fields_for :entryable do |ef| %>
       <%= ef.collection_select :category_id, categories, :id, :name, { prompt: t(".category_prompt"), label: t(".category"), variant: :badge, searchable: true } %>
     <% end %>
-    <%= f.date_field :date, label: t(".date"), required: true, min: Entry.min_supported_date, max: Date.current, value: Date.current %>
+    
+    <%= f.date_field :date, 
+      label: t(".date"), 
+      required: true, 
+      min: Entry.min_supported_date, 
+      max: Date.current, 
+      value: f.object.date || Date.current,
+      data: { transaction_form_target: "date", action: "change->transaction-form#checkCurrencyDifference" } %>
+
+    <% convert_input = capture do %>
+      <%= f.fields_for :entryable do |ef| %>
+        <%= ef.number_field :exchange_rate,
+          label: t("shared.exchange_rate_tabs.exchange_rate"),
+          min: "0.00000000000001",
+          step: "0.00000000000001",
+          placeholder: "1.0",
+          class: "form-field__input",
+          data: {
+            transaction_form_target: "exchangeRateField",
+            action: "input->transaction-form#onConvertExchangeRateChange"
+          } %>
+      <% end %>
+    <% end %>
+
+    <% destination_input = capture do %>
+      <%= number_field_tag :destination_amount,
+        nil,
+        id: "transaction_form_destination_amount",
+        class: "form-field__input",
+        min: "0",
+        step: "0.00000001",
+        placeholder: "92",
+        data: {
+          transaction_form_target: "destinationAmount",
+          action: "input->transaction-form#onCalculateRateDestinationAmountChange"
+        } %>
+    <% end %>
+
+    <%= render "shared/exchange_rate_tabs",
+      controller_id: "transaction-form",
+      controller_key: "transaction_form",
+      help_text: t("shared.exchange_rate_tabs.exchange_rate_help"),
+      convert_tab_label: t("shared.exchange_rate_tabs.convert_tab"),
+      calculate_rate_tab_label: t("shared.exchange_rate_tabs.calculate_rate_tab"),
+      destination_amount_label: t("shared.exchange_rate_tabs.destination_amount"),
+      exchange_rate_label: t("shared.exchange_rate_tabs.exchange_rate"),
+      convert_input: convert_input,
+      destination_input: destination_input %>
   </section>
 
   <%= render DS::Disclosure.new(title: t(".details")) do %>
diff --git a/app/views/transfers/_form.html.erb b/app/views/transfers/_form.html.erb
index 39684a9cd..a7696692a 100644
--- a/app/views/transfers/_form.html.erb
+++ b/app/views/transfers/_form.html.erb
@@ -1,4 +1,5 @@
-<%= styled_form_with model: transfer, class: "space-y-4", data: { turbo_frame: "_top", controller: "transfer-form" } do |f| %>
+<% account_currencies = Current.family.accounts.map { |a| [a.id, a.currency] }.to_h.to_json %>
+<%= styled_form_with model: transfer, class: "space-y-4", data: { turbo_frame: "_top", controller: "transfer-form", transfer_form_exchange_rate_url_value: exchange_rate_path, transfer_form_account_currencies_value: account_currencies } do |f| %>
   <% if transfer.errors.present? %>
     <div class="text-destructive flex items-center gap-2">
       <%= icon "circle-alert", size: "sm" %>
@@ -27,10 +28,49 @@
   <% end %>
 
   <section class="space-y-2">
-    <%= f.collection_select :from_account_id, @accounts, :id, :name, { prompt: t(".select_account"), label: t(".from"), selected: @from_account_id, variant: :logo }, required: true %>
-    <%= f.collection_select :to_account_id, @accounts, :id, :name, { prompt: t(".select_account"), label: t(".to"), variant: :logo }, required: true %>
-    <%= f.number_field :amount, label: t(".amount"), required: true, min: 0, placeholder: "100", step: 0.00000001 %>
-    <%= f.date_field :date, value: transfer.inflow_transaction&.entry&.date || Date.current, label: t(".date"), required: true, max: Date.current %>
+    <%= f.collection_select :from_account_id, @accounts, :id, :name, { prompt: t(".select_account"), label: t(".from"), selected: @from_account_id, variant: :logo }, { required: true, data: { transfer_form_target: "fromAccount", action: "change->transfer-form#checkCurrencyDifference" } } %>
+    <%= f.collection_select :to_account_id, @accounts, :id, :name, { prompt: t(".select_account"), label: t(".to"), variant: :logo }, { required: true, data: { transfer_form_target: "toAccount", action: "change->transfer-form#checkCurrencyDifference" } } %>
+    
+    <%= f.date_field :date, value: transfer.inflow_transaction&.entry&.date || Date.current, label: t(".date"), required: true, max: Date.current, data: { transfer_form_target: "date", action: "change->transfer-form#checkCurrencyDifference" } %>
+    
+    <%= f.number_field :amount, label: t(".source_amount"), required: true, min: 0, placeholder: "100", step: 0.00000001, data: { transfer_form_target: "amount", action: "input->transfer-form#onSourceAmountChange" } %>
+    
+    <% convert_input = capture do %>
+      <%= f.number_field :exchange_rate,
+        label: t("shared.exchange_rate_tabs.exchange_rate"),
+        min: "0.00000000000001",
+        step: "0.00000000000001",
+        placeholder: "1.0",
+        class: "form-field__input",
+        data: {
+          transfer_form_target: "exchangeRateField",
+          action: "input->transfer-form#onConvertExchangeRateChange"
+        } %>
+    <% end %>
+
+    <% destination_input = capture do %>
+      <%= tag.input type: "number",
+        id: "transfer_form_destination_amount",
+        class: "form-field__input",
+        min: "0",
+        step: "0.00000001",
+        placeholder: "92",
+        data: {
+          transfer_form_target: "destinationAmount",
+          action: "input->transfer-form#onCalculateRateDestinationAmountChange"
+        } %>
+    <% end %>
+
+    <%= render "shared/exchange_rate_tabs",
+      controller_id: "transfer-form",
+      controller_key: "transfer_form",
+      help_text: t("shared.exchange_rate_tabs.exchange_rate_help"),
+      convert_tab_label: t("shared.exchange_rate_tabs.convert_tab"),
+      calculate_rate_tab_label: t("shared.exchange_rate_tabs.calculate_rate_tab"),
+      destination_amount_label: t("shared.exchange_rate_tabs.destination_amount"),
+      exchange_rate_label: t("shared.exchange_rate_tabs.exchange_rate"),
+      convert_input: convert_input,
+      destination_input: destination_input %>
   </section>
 
   <section>
diff --git a/config/locales/views/shared/ca.yml b/config/locales/views/shared/ca.yml
index 39c098d23..7dcbd7a99 100644
--- a/config/locales/views/shared/ca.yml
+++ b/config/locales/views/shared/ca.yml
@@ -8,6 +8,12 @@ ca:
       title: Segur que vols continuar?
     money_field:
       label: Import
+    exchange_rate_tabs:
+      calculate_rate_tab: Calcular la taxa FX
+      convert_tab: Convertir amb la taxa FX
+      destination_amount: Quantitat de destinació
+      exchange_rate: Taxa de canvi
+      exchange_rate_help: Trieu com introduir la quantitat.
     syncing_notice:
       syncing: S'estan sincronitzant les dades dels comptes...
     transaction_tabs:
diff --git a/config/locales/views/shared/de.yml b/config/locales/views/shared/de.yml
index 1b0cfb1bf..f0af087e2 100644
--- a/config/locales/views/shared/de.yml
+++ b/config/locales/views/shared/de.yml
@@ -8,6 +8,12 @@ de:
       title: Bist du sicher
     money_field:
       label: Betrag
+    exchange_rate_tabs:
+      calculate_rate_tab: FX-Kurs berechnen
+      convert_tab: Mit FX-Kurs konvertieren
+      destination_amount: Zielbetrag
+      exchange_rate: Wechselkurs
+      exchange_rate_help: Wählen Sie, wie Sie den Betrag eingeben möchten.
     syncing_notice:
       syncing: Kontodaten werden synchronisiert...
     trend_change:
diff --git a/config/locales/views/shared/en.yml b/config/locales/views/shared/en.yml
index f94797c77..98a6e479a 100644
--- a/config/locales/views/shared/en.yml
+++ b/config/locales/views/shared/en.yml
@@ -8,6 +8,12 @@ en:
       title: Are you sure?
     money_field:
       label: Amount
+    exchange_rate_tabs:
+      calculate_rate_tab: Calculate FX rate
+      convert_tab: Convert with FX rate
+      destination_amount: Destination amount
+      exchange_rate: Exchange rate
+      exchange_rate_help: Choose how to enter the amount.
     syncing_notice:
       syncing: Syncing accounts data...
     require_admin: "Only admins can perform this action"
diff --git a/config/locales/views/shared/es.yml b/config/locales/views/shared/es.yml
index db6ceb073..4b3f5914f 100644
--- a/config/locales/views/shared/es.yml
+++ b/config/locales/views/shared/es.yml
@@ -8,6 +8,12 @@ es:
       title: ¿Estás seguro?
     money_field:
       label: Importe
+    exchange_rate_tabs:
+      calculate_rate_tab: Calcular tasa
+      convert_tab: Convertir con tasa
+      destination_amount: Importe de destino
+      exchange_rate: Tasa de cambio
+      exchange_rate_help: Elige cómo introducir el importe.
     syncing_notice:
       syncing: Sincronizando datos de cuentas...
     trend_change:
diff --git a/config/locales/views/shared/fr.yml b/config/locales/views/shared/fr.yml
index 0ecdb2d32..8e95f5bbf 100644
--- a/config/locales/views/shared/fr.yml
+++ b/config/locales/views/shared/fr.yml
@@ -20,6 +20,12 @@ fr:
       title: Êtes-vous sûr ?
     money_field:
       label: Montant
+    exchange_rate_tabs:
+      calculate_rate_tab: Calculer le taux FX
+      convert_tab: Convertir avec le taux FX
+      destination_amount: Montant de destination
+      exchange_rate: Taux de change
+      exchange_rate_help: Choisissez comment entrer le montant.
     syncing_notice:
       syncing: Synchronisation des données de compte...
     trend_change:
diff --git a/config/locales/views/shared/nb.yml b/config/locales/views/shared/nb.yml
index a96b72952..c4e6eb8b0 100644
--- a/config/locales/views/shared/nb.yml
+++ b/config/locales/views/shared/nb.yml
@@ -1,14 +1,20 @@
----
-nb:
-  shared:
-    confirm_modal:
-      accept: Bekreft
-      body_html: "<p>Du vil ikke kunne angre denne beslutningen</p>"
-      cancel: Avbryt
-      title: Er du sikker?
-    money_field:
-      label: Beløp
-    syncing_notice:
-      syncing: Synkroniserer kontodata...
-    trend_change:
+---
+nb:
+  shared:
+    confirm_modal:
+      accept: Bekreft
+      body_html: "<p>Du vil ikke kunne angre denne beslutningen</p>"
+      cancel: Avbryt
+      title: Er du sikker?
+    money_field:
+      label: Beløp
+    exchange_rate_tabs:
+      calculate_rate_tab: Beregn FX-kurs
+      convert_tab: Konverter med FX-kurs
+      destination_amount: Beløp for destinasjon
+      exchange_rate: Vekslingskurs
+      exchange_rate_help: Velg hvordan du vil fylle inn beløpet.
+    syncing_notice:
+      syncing: Synkroniserer kontodata...
+    trend_change:
       no_change: "ingen endring"
\ No newline at end of file
diff --git a/config/locales/views/shared/nl.yml b/config/locales/views/shared/nl.yml
index 569c00e0d..a63b576d0 100644
--- a/config/locales/views/shared/nl.yml
+++ b/config/locales/views/shared/nl.yml
@@ -8,6 +8,12 @@ nl:
       title: Weet u het zeker?
     money_field:
       label: Bedrag
+    exchange_rate_tabs:
+      calculate_rate_tab: FX-tarief berekenen
+      convert_tab: Converteren met FX-tarief
+      destination_amount: Doelbedrag
+      exchange_rate: Wisselkoers
+      exchange_rate_help: Kies hoe u het bedrag wilt invoeren.
     syncing_notice:
       syncing: Accountsgegevens synchroniseren...
     trend_change:
diff --git a/config/locales/views/shared/pt-BR.yml b/config/locales/views/shared/pt-BR.yml
index cd14facf5..73fc47727 100644
--- a/config/locales/views/shared/pt-BR.yml
+++ b/config/locales/views/shared/pt-BR.yml
@@ -8,6 +8,12 @@ pt-BR:
       title: Tem certeza?
     money_field:
       label: Valor
+    exchange_rate_tabs:
+      calculate_rate_tab: Calcular taxa de câmbio
+      convert_tab: Converter com taxa de câmbio
+      destination_amount: Valor de destino
+      exchange_rate: Taxa de câmbio
+      exchange_rate_help: Escolha como inserir o valor.
     syncing_notice:
       syncing: Sincronizando dados das contas...
     trend_change:
diff --git a/config/locales/views/shared/ro.yml b/config/locales/views/shared/ro.yml
index b97866bd3..9cb591e89 100644
--- a/config/locales/views/shared/ro.yml
+++ b/config/locales/views/shared/ro.yml
@@ -8,6 +8,12 @@ ro:
       title: Ești sigur?
     money_field:
       label: Sumă
+    exchange_rate_tabs:
+      calculate_rate_tab: Calculați rata FX
+      convert_tab: Convertire cu rata FX
+      destination_amount: Suma de destinație
+      exchange_rate: Rata de schimb
+      exchange_rate_help: Alege cum dorești să introduci suma.
     syncing_notice:
       syncing: Se sincronizează datele conturilor...
     trend_change:
diff --git a/config/locales/views/shared/tr.yml b/config/locales/views/shared/tr.yml
index 8970dc097..045e211c2 100644
--- a/config/locales/views/shared/tr.yml
+++ b/config/locales/views/shared/tr.yml
@@ -8,6 +8,12 @@ tr:
       title: Emin misiniz?
     money_field:
       label: Tutar
+    exchange_rate_tabs:
+      calculate_rate_tab: Döviz Kuru Hesapla
+      convert_tab: Döviz Kuru ile Dönüştür
+      destination_amount: Hedef Tutar
+      exchange_rate: Döviz Kuru
+      exchange_rate_help: Tutar girişiniz için yöntemi seçin.
     syncing_notice:
       syncing: Hesap verileri senkronize ediliyor...
     trend_change:
diff --git a/config/locales/views/shared/zh-CN.yml b/config/locales/views/shared/zh-CN.yml
index d37cc3c3f..a84a48379 100644
--- a/config/locales/views/shared/zh-CN.yml
+++ b/config/locales/views/shared/zh-CN.yml
@@ -8,6 +8,12 @@ zh-CN:
       title: 确定要执行此操作？
     money_field:
       label: 金额
+    exchange_rate_tabs:
+      calculate_rate_tab: 计算汇率
+      convert_tab: 用汇率转换
+      destination_amount: 目标金额
+      exchange_rate: 汇率
+      exchange_rate_help: 选择如何输入金额。
     syncing_notice:
       syncing: 账户数据同步中...
     transaction_tabs:
diff --git a/config/locales/views/shared/zh-TW.yml b/config/locales/views/shared/zh-TW.yml
index a29edfe67..b1e193f22 100644
--- a/config/locales/views/shared/zh-TW.yml
+++ b/config/locales/views/shared/zh-TW.yml
@@ -8,6 +8,12 @@ zh-TW:
       title: 您確定嗎？
     money_field:
       label: 金額
+    exchange_rate_tabs:
+      calculate_rate_tab: 計算匯率
+      convert_tab: 用匯率轉換
+      destination_amount: 目標金額
+      exchange_rate: 匯率
+      exchange_rate_help: 選擇如何輸入金額。
     syncing_notice:
       syncing: 正在同步帳戶資料...
     trend_change:
diff --git a/config/locales/views/transfers/en.yml b/config/locales/views/transfers/en.yml
index 669bae2d3..9116f4f6b 100644
--- a/config/locales/views/transfers/en.yml
+++ b/config/locales/views/transfers/en.yml
@@ -7,11 +7,19 @@ en:
       success: Transfer removed
     form:
       amount: Amount
+      calculate_rate_tab: Calculate FX rate
+      convert_tab: Convert with FX rate
       date: Date
+      destination_amount: Destination amount
+      destination_amount_display: "Destination amount: %{amount}"
+      exchange_rate: Exchange rate
+      exchange_rate_display: "Exchange rate: %{rate}"
+      exchange_rate_help: Choose how to enter the transfer amount.
       expense: Expense
       from: From
       income: Income
       select_account: Select account
+      source_amount: Source amount
       submit: Create transfer
       to: To
       transfer: Transfer
diff --git a/config/locales/views/transfers/es.yml b/config/locales/views/transfers/es.yml
index f16061fa3..419c9b719 100644
--- a/config/locales/views/transfers/es.yml
+++ b/config/locales/views/transfers/es.yml
@@ -7,11 +7,19 @@ es:
       success: Transferencia eliminada
     form:
       amount: Importe
+      calculate_rate_tab: Calcular tasa
+      convert_tab: Convertir con tasa
       date: Fecha
+      destination_amount: Importe de destino
+      destination_amount_display: "Importe de destino: %{amount}"
+      exchange_rate: Tasa de cambio
+      exchange_rate_display: "Tasa de cambio: %{rate}"
+      exchange_rate_help: Elige cómo introducir el importe de la transferencia.
       expense: Gasto
       from: Desde
       income: Ingreso
       select_account: Seleccionar cuenta
+      source_amount: Importe de origen
       submit: Crear transferencia
       to: Hacia
       transfer: Transferencia
diff --git a/config/routes.rb b/config/routes.rb
index 8082c1efe..5f723eed0 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -249,6 +249,8 @@ Rails.application.routes.draw do
     end
   end
 
+  get :exchange_rate, to: "exchange_rates#show"
+
   resources :transfers, only: %i[new create destroy show update]
 
   resources :imports, only: %i[index new show create update destroy] do
diff --git a/lib/money.rb b/lib/money.rb
index ed1e00d48..0d1e73a88 100644
--- a/lib/money.rb
+++ b/lib/money.rb
@@ -39,16 +39,30 @@ class Money
     validate!
   end
 
-  def exchange_to(other_currency, date: Date.current, fallback_rate: nil)
+  # Exchange money to another currency
+  # Params:
+  #   other_currency: target currency code (e.g. "USD")
+  #   date: date for historical rates (default: Date.current)
+  #   custom_rate: explicit exchange rate to use (skips lookup if provided, including nil check)
+  # Priority:
+  #   1. Use custom_rate if explicitly provided (not nil)
+  #   2. Look up rate via store.find_or_fetch_rate
+  #   3. Raise ConversionError if no valid rate available
+  def exchange_to(other_currency, date: Date.current, custom_rate: nil)
     iso_code = currency.iso_code
     other_iso_code = Money::Currency.new(other_currency).iso_code
 
     if iso_code == other_iso_code
       self
     else
-      exchange_rate = store.find_or_fetch_rate(from: iso_code, to: other_iso_code, date: date)&.rate || fallback_rate
+      # Use custom rate if provided, otherwise look it up
+      if custom_rate.present?
+        exchange_rate = custom_rate.to_d
+      else
+        exchange_rate = store.find_or_fetch_rate(from: iso_code, to: other_iso_code, date: date)&.rate
+      end
 
-      raise ConversionError.new(from_currency: iso_code, to_currency: other_iso_code, date: date) unless exchange_rate
+      raise ConversionError.new(from_currency: iso_code, to_currency: other_iso_code, date: date) unless exchange_rate && exchange_rate > 0
 
       Money.new(amount * exchange_rate, other_iso_code)
     end
diff --git a/test/application_system_test_case.rb b/test/application_system_test_case.rb
index 69724cda0..313c12efe 100644
--- a/test/application_system_test_case.rb
+++ b/test/application_system_test_case.rb
@@ -65,4 +65,18 @@ class ApplicationSystemTestCase < ActionDispatch::SystemTestCase
         yield
       end
     end
+
+    # Interact with DS::Select custom dropdown components.
+    # DS::Select renders as a button + listbox — not a native <select> — so
+    # Capybara's built-in `select(value, from:)` does not work with it.
+    def select_ds(label_text, record)
+      field_label = find("label", exact_text: label_text)
+      container = field_label.ancestor("div.relative")
+      container.find("button").click
+      if container.has_selector?("input[type='search']", visible: true)
+        container.find("input[type='search']", visible: true).set(record.name)
+      end
+      listbox = container.find("[role='listbox']", visible: true)
+      listbox.find("[role='option'][data-value='#{record.id}']", visible: true).click
+    end
 end
diff --git a/test/controllers/exchange_rates_controller_test.rb b/test/controllers/exchange_rates_controller_test.rb
new file mode 100644
index 000000000..13b7b6965
--- /dev/null
+++ b/test/controllers/exchange_rates_controller_test.rb
@@ -0,0 +1,173 @@
+require "test_helper"
+
+class ExchangeRatesControllerTest < ActionDispatch::IntegrationTest
+  setup do
+    @user = users(:family_admin)
+    sign_in @user
+  end
+
+  test "returns rate for different currencies" do
+    ExchangeRate.create!(
+      from_currency: "EUR",
+      to_currency: "USD",
+      date: Date.current,
+      rate: 1.2
+    )
+
+    get exchange_rate_url, params: {
+      from: "EUR",
+      to: "USD",
+      date: Date.current
+    }
+
+    assert_response :success
+    json_response = JSON.parse(response.body)
+    assert_equal 1.2, json_response["rate"]
+  end
+
+  test "returns same_currency flag for matching currencies" do
+    get exchange_rate_url, params: {
+      from: "USD",
+      to: "USD"
+    }
+
+    assert_response :success
+    json_response = JSON.parse(response.body)
+    assert json_response["same_currency"]
+    assert_equal 1.0, json_response["rate"]
+  end
+
+  test "uses provided date for rate lookup" do
+    custom_date = 3.days.ago.to_date
+    ExchangeRate.create!(
+      from_currency: "EUR",
+      to_currency: "USD",
+      date: custom_date,
+      rate: 1.25
+    )
+
+    get exchange_rate_url, params: {
+      from: "EUR",
+      to: "USD",
+      date: custom_date
+    }
+
+    assert_response :success
+    json_response = JSON.parse(response.body)
+    assert_equal 1.25, json_response["rate"]
+  end
+
+  test "defaults to current date when not provided" do
+    ExchangeRate.create!(
+      from_currency: "EUR",
+      to_currency: "USD",
+      date: Date.current,
+      rate: 1.2
+    )
+
+    get exchange_rate_url, params: {
+      from: "EUR",
+      to: "USD"
+    }
+
+    assert_response :success
+    json_response = JSON.parse(response.body)
+    assert_equal 1.2, json_response["rate"]
+  end
+
+  test "returns 400 when from currency is missing" do
+    get exchange_rate_url, params: {
+      to: "USD"
+    }
+
+    assert_response :bad_request
+    json_response = JSON.parse(response.body)
+    assert_equal "from and to currencies are required", json_response["error"]
+  end
+
+  test "returns 400 when to currency is missing" do
+    get exchange_rate_url, params: {
+      from: "EUR"
+    }
+
+    assert_response :bad_request
+    json_response = JSON.parse(response.body)
+    assert_equal "from and to currencies are required", json_response["error"]
+  end
+
+  test "returns 400 on invalid date format" do
+    get exchange_rate_url, params: {
+      from: "EUR",
+      to: "USD",
+      date: "not-a-date"
+    }
+
+    assert_response :bad_request
+    json_response = JSON.parse(response.body)
+    assert_equal "Invalid date format", json_response["error"]
+  end
+
+  test "returns 404 when rate not found" do
+    get exchange_rate_url, params: {
+      from: "EUR",
+      to: "USD",
+      date: Date.current
+    }
+
+    assert_response :not_found
+    json_response = JSON.parse(response.body)
+    assert_equal "Exchange rate not found", json_response["error"]
+  end
+
+  test "handles uppercase and lowercase currency codes" do
+    ExchangeRate.create!(
+      from_currency: "EUR",
+      to_currency: "USD",
+      date: Date.current,
+      rate: 1.2
+    )
+
+    get exchange_rate_url, params: {
+      from: "eur",
+      to: "usd"
+    }
+
+    assert_response :success
+    json_response = JSON.parse(response.body)
+    assert_equal 1.2, json_response["rate"]
+  end
+
+  test "returns numeric rate even when object has rate method" do
+    # Create mock object that returns a rate
+    rate_obj = OpenStruct.new(rate: 1.2)
+
+    ExchangeRate.expects(:find_or_fetch_rate)
+                .with(from: "EUR", to: "USD", date: Date.current)
+                .returns(rate_obj)
+
+    get exchange_rate_url, params: {
+      from: "EUR",
+      to: "USD"
+    }
+
+    assert_response :success
+    json_response = JSON.parse(response.body)
+    assert_equal 1.2, json_response["rate"]
+    assert_instance_of Float, json_response["rate"]
+  end
+
+  test "returns error when find_or_fetch_rate raises exception" do
+    ExchangeRate.expects(:find_or_fetch_rate)
+                .with(from: "EUR", to: "USD", date: Date.current)
+                .raises(StandardError, "Rate fetch failed")
+
+    get exchange_rate_url, params: {
+      from: "EUR",
+      to: "USD"
+    }
+
+    assert_response :bad_request
+    json_response = JSON.parse(response.body)
+    assert_equal "Failed to fetch exchange rate", json_response["error"]
+  end
+end
diff --git a/test/controllers/transactions_controller_test.rb b/test/controllers/transactions_controller_test.rb
index 8bb91aa85..8c79b793e 100644
--- a/test/controllers/transactions_controller_test.rb
+++ b/test/controllers/transactions_controller_test.rb
@@ -390,4 +390,157 @@ end
     assert_not entry.import_locked?
     assert_not entry.protected_from_sync?
   end
+
+  test "exchange_rate endpoint returns rate for different currencies" do
+    ExchangeRate.expects(:find_or_fetch_rate)
+                .with(from: "EUR", to: "USD", date: Date.current)
+                .returns(1.2)
+
+    get exchange_rate_url, params: {
+      from: "EUR",
+      to: "USD",
+      date: Date.current
+    }
+
+    assert_response :success
+    json_response = JSON.parse(response.body)
+    assert_equal 1.2, json_response["rate"]
+  end
+
+  test "exchange_rate endpoint returns same_currency for matching currencies" do
+    get exchange_rate_url, params: {
+      from: "USD",
+      to: "USD"
+    }
+
+    assert_response :success
+    json_response = JSON.parse(response.body)
+    assert json_response["same_currency"]
+    assert_equal 1.0, json_response["rate"]
+  end
+
+  test "exchange_rate endpoint uses provided date" do
+    custom_date = 3.days.ago.to_date
+    ExchangeRate.expects(:find_or_fetch_rate)
+                .with(from: "EUR", to: "USD", date: custom_date)
+                .returns(1.25)
+
+    get exchange_rate_url, params: {
+      from: "EUR",
+      to: "USD",
+      date: custom_date
+    }
+
+    assert_response :success
+    json_response = JSON.parse(response.body)
+    assert_equal 1.25, json_response["rate"]
+  end
+
+  test "exchange_rate endpoint returns 400 when from currency is missing" do
+    get exchange_rate_url, params: {
+      to: "USD"
+    }
+
+    assert_response :bad_request
+    json_response = JSON.parse(response.body)
+    assert_equal "from and to currencies are required", json_response["error"]
+  end
+
+  test "exchange_rate endpoint returns 400 when to currency is missing" do
+    get exchange_rate_url, params: {
+      from: "EUR"
+    }
+
+    assert_response :bad_request
+    json_response = JSON.parse(response.body)
+    assert_equal "from and to currencies are required", json_response["error"]
+  end
+
+  test "exchange_rate endpoint returns 400 on invalid date format" do
+    get exchange_rate_url, params: {
+      from: "EUR",
+      to: "USD",
+      date: "not-a-date"
+    }
+
+    assert_response :bad_request
+    json_response = JSON.parse(response.body)
+    assert_equal "Invalid date format", json_response["error"]
+  end
+
+  test "exchange_rate endpoint returns 404 when rate not found" do
+    ExchangeRate.expects(:find_or_fetch_rate)
+                .with(from: "EUR", to: "USD", date: Date.current)
+                .returns(nil)
+
+    get exchange_rate_url, params: {
+      from: "EUR",
+      to: "USD"
+    }
+
+    assert_response :not_found
+    json_response = JSON.parse(response.body)
+    assert_equal "Exchange rate not found", json_response["error"]
+  end
+
+  test "creates transaction with custom exchange rate" do
+    account = @user.family.accounts.create!(
+      name: "USD Account",
+      currency: "USD",
+      balance: 1000,
+      accountable: Depository.new
+    )
+
+    assert_difference [ "Entry.count", "Transaction.count" ], 1 do
+      post transactions_url, params: {
+        entry: {
+          account_id: account.id,
+          name: "EUR transaction with custom rate",
+          date: Date.current,
+          currency: "EUR",
+          amount: 100,
+          nature: "outflow",
+          entryable_type: "Transaction",
+          entryable_attributes: {
+            category_id: Category.first.id,
+            exchange_rate: "1.5"
+          }
+        }
+      }
+    end
+
+    created_entry = Entry.order(:created_at).last
+    assert_equal "EUR", created_entry.currency
+    assert_equal 100, created_entry.amount
+    assert_equal 1.5, created_entry.transaction.extra["exchange_rate"]
+  end
+
+  test "creates transaction without custom exchange rate" do
+    account = @user.family.accounts.create!(
+      name: "USD Account",
+      currency: "USD",
+      balance: 1000,
+      accountable: Depository.new
+    )
+
+    assert_difference [ "Entry.count", "Transaction.count" ], 1 do
+      post transactions_url, params: {
+        entry: {
+          account_id: account.id,
+          name: "EUR transaction without custom rate",
+          date: Date.current,
+          currency: "EUR",
+          amount: 100,
+          nature: "outflow",
+          entryable_type: "Transaction",
+          entryable_attributes: {
+            category_id: Category.first.id
+          }
+        }
+      }
+    end
+
+    created_entry = Entry.order(:created_at).last
+    assert_nil created_entry.transaction.extra["exchange_rate"]
+  end
 end
diff --git a/test/controllers/transfers_controller_test.rb b/test/controllers/transfers_controller_test.rb
index 9959f45b2..ca42a51fa 100644
--- a/test/controllers/transfers_controller_test.rb
+++ b/test/controllers/transfers_controller_test.rb
@@ -25,6 +25,143 @@ class TransfersControllerTest < ActionDispatch::IntegrationTest
     end
   end
 
+  test "can create transfer with custom exchange rate" do
+    usd_account = accounts(:depository)
+    eur_account = users(:family_admin).family.accounts.create!(
+      name: "EUR Account",
+      balance: 1000,
+      currency: "EUR",
+      accountable: Depository.new
+    )
+
+    assert_equal "USD", usd_account.currency
+    assert_equal "EUR", eur_account.currency
+
+    assert_difference "Transfer.count", 1 do
+      post transfers_url, params: {
+        transfer: {
+          from_account_id: usd_account.id,
+          to_account_id: eur_account.id,
+          date: Date.current,
+          amount: 100,
+          exchange_rate: 0.92
+        }
+      }
+    end
+
+    transfer = Transfer.where(
+      "outflow_transaction_id IN (?) AND inflow_transaction_id IN (?)",
+      usd_account.transactions.pluck(:id),
+      eur_account.transactions.pluck(:id)
+    ).last
+    assert_not_nil transfer
+    assert_equal "USD", transfer.outflow_transaction.entry.currency
+    assert_equal "EUR", transfer.inflow_transaction.entry.currency
+    assert_equal 100, transfer.outflow_transaction.entry.amount
+    assert_in_delta(-92, transfer.inflow_transaction.entry.amount, 0.01)
+  end
+
+  test "exchange_rate endpoint returns 400 when from currency is missing" do
+    get exchange_rate_url, params: {
+      to: "USD"
+    }
+
+    assert_response :bad_request
+    json_response = JSON.parse(response.body)
+    assert_equal "from and to currencies are required", json_response["error"]
+  end
+
+  test "exchange_rate endpoint returns 400 when to currency is missing" do
+    get exchange_rate_url, params: {
+      from: "EUR"
+    }
+
+    assert_response :bad_request
+    json_response = JSON.parse(response.body)
+    assert_equal "from and to currencies are required", json_response["error"]
+  end
+
+  test "exchange_rate endpoint returns 400 on invalid date format" do
+    get exchange_rate_url, params: {
+      from: "EUR",
+      to: "USD",
+      date: "not-a-date"
+    }
+
+    assert_response :bad_request
+    json_response = JSON.parse(response.body)
+    assert_equal "Invalid date format", json_response["error"]
+  end
+
+  test "exchange_rate endpoint returns rate for different currencies" do
+    ExchangeRate.expects(:find_or_fetch_rate)
+                .with(from: "USD", to: "EUR", date: Date.current)
+                .returns(OpenStruct.new(rate: 0.92))
+
+    get exchange_rate_url, params: {
+      from: "USD",
+      to: "EUR",
+      date: Date.current.to_s
+    }
+
+    assert_response :success
+    json_response = JSON.parse(response.body)
+    assert_equal 0.92, json_response["rate"]
+  end
+
+  test "exchange_rate endpoint returns error when exchange rate unavailable" do
+    ExchangeRate.expects(:find_or_fetch_rate)
+                .with(from: "USD", to: "EUR", date: Date.current)
+                .returns(nil)
+
+    get exchange_rate_url, params: {
+      from: "USD",
+      to: "EUR",
+      date: Date.current.to_s
+    }
+
+    assert_response :not_found
+    json_response = JSON.parse(response.body)
+    assert_equal "Exchange rate not found", json_response["error"]
+  end
+
+  test "cannot create transfer when exchange rate unavailable and no custom rate provided" do
+    usd_account = accounts(:depository)
+    eur_account = users(:family_admin).family.accounts.create!(
+      name: "EUR Account",
+      balance: 1000,
+      currency: "EUR",
+      accountable: Depository.new
+    )
+
+    ExchangeRate.stubs(:find_or_fetch_rate).returns(nil)
+
+    assert_no_difference "Transfer.count" do
+      post transfers_url, params: {
+        transfer: {
+          from_account_id: usd_account.id,
+          to_account_id: eur_account.id,
+          date: Date.current,
+          amount: 100
+        }
+      }
+    end
+
+    assert_response :unprocessable_entity
+  end
+
+  test "exchange_rate endpoint returns same_currency for matching currencies" do
+    get exchange_rate_url, params: {
+      from: "USD",
+      to: "USD"
+    }
+
+    assert_response :success
+    json_response = JSON.parse(response.body)
+    assert_equal true, json_response["same_currency"]
+    assert_equal 1.0, json_response["rate"]
+  end
+
   test "soft deletes transfer" do
     assert_difference -> { Transfer.count }, -1 do
       delete transfer_url(transfers(:one))
diff --git a/test/lib/money_test.rb b/test/lib/money_test.rb
index 5c18105aa..c036f8aa4 100644
--- a/test/lib/money_test.rb
+++ b/test/lib/money_test.rb
@@ -180,18 +180,27 @@ class MoneyTest < ActiveSupport::TestCase
     assert_equal Money.new(1000).exchange_to(:eur), Money.new(1000 * 1.2, :eur)
   end
 
-  test "raises when no conversion rate available and no fallback rate provided" do
+  test "raises when no conversion rate available and no fallback provided" do
     ExchangeRate.expects(:find_or_fetch_rate).returns(nil)
 
-    assert_raises Money::ConversionError do
+    assert_raises(Money::ConversionError) do
       Money.new(1000).exchange_to(:jpy)
     end
   end
 
-  test "converts currency with a fallback rate" do
-    ExchangeRate.expects(:find_or_fetch_rate).returns(nil).twice
+  test "uses custom rate when provided" do
+    ExchangeRate.expects(:find_or_fetch_rate).never
 
-    assert_equal 0, Money.new(1000).exchange_to(:jpy, fallback_rate: 0)
-    assert_equal Money.new(1000, :jpy), Money.new(1000, :usd).exchange_to(:jpy, fallback_rate: 1)
+    assert_equal Money.new(1250, :jpy), Money.new(1000, :usd).exchange_to(:jpy, custom_rate: 1.25)
+  end
+
+  test "raises error when custom rate is invalid" do
+  assert_raises(Money::ConversionError) do
+    Money.new(1000).exchange_to(:jpy, custom_rate: 0)
+  end
+
+  assert_raises(Money::ConversionError) do
+    Money.new(1000).exchange_to(:jpy, custom_rate: -1)
   end
 end
+end
diff --git a/test/models/balance/forward_calculator_test.rb b/test/models/balance/forward_calculator_test.rb
index 3d2c9fa26..22c8a5a61 100644
--- a/test/models/balance/forward_calculator_test.rb
+++ b/test/models/balance/forward_calculator_test.rb
@@ -693,8 +693,8 @@ class Balance::ForwardCalculatorTest < ActiveSupport::TestCase
   end
 
   test "multi-currency account falls back to full recalc so late exchange rate imports are picked up" do
-    # Step 1: Create account with a EUR entry but NO exchange rate yet.
-    # SyncCache will use fallback_rate: 1, so the €500 entry is treated as $500.
+    # Step 1: Create account with a EUR entry and a stale exchange rate (1:1 EUR→USD).
+    # This simulates an initial sync where an imprecise rate is available.
     account = create_account_with_ledger(
       account: { type: Depository, currency: "USD" },
       entries: [
@@ -703,14 +703,16 @@ class Balance::ForwardCalculatorTest < ActiveSupport::TestCase
         { type: "transaction", date: 2.days.ago.to_date, amount: -500, currency: "EUR" }
       ]
     )
+    ExchangeRate.create!(date: 2.days.ago.to_date, from_currency: "EUR", to_currency: "USD", rate: 1.0)
 
-    # First full sync — balances computed with fallback rate (1:1 EUR→USD).
+    # First full sync — balances computed with stale rate (1:1 EUR→USD).
+    # opening 100 + $100 txn + €500*1.0 = $700
     Balance::Materializer.new(account, strategy: :forward).materialize_balances
     stale_balance = account.balances.find_by(date: 2.days.ago.to_date)
     assert stale_balance, "Balance should exist after full sync"
 
-    # Step 2: Exchange rate arrives later (e.g. daily cron imports it).
-    ExchangeRate.create!(date: 2.days.ago.to_date, from_currency: "EUR", to_currency: "USD", rate: 1.2)
+    # Step 2: Corrected exchange rate arrives later (e.g. daily cron imports it).
+    ExchangeRate.find_by!(date: 2.days.ago.to_date, from_currency: "EUR", to_currency: "USD").update!(rate: 1.2)
 
     # Step 3: Next sync requests incremental from today — but the guard should
     # force a full recalc because the account has multi-currency entries.
@@ -725,7 +727,7 @@ class Balance::ForwardCalculatorTest < ActiveSupport::TestCase
     # The EUR entry on 2.days.ago is now converted at 1.2, so the balance
     # picks up the corrected rate: opening 100 + $100 txn + €500*1.2 = $800
     # (without the guard, incremental mode would have seeded from the stale
-    # $700 balance computed with fallback_rate 1, and never corrected it).
+    # $700 balance computed with rate 1.0, and never corrected it).
     corrected = result.find { |b| b.date == 2.days.ago.to_date }
     assert corrected
     assert_equal 800, corrected.balance,
diff --git a/test/models/balance/sync_cache_test.rb b/test/models/balance/sync_cache_test.rb
new file mode 100644
index 000000000..0edf1d30d
--- /dev/null
+++ b/test/models/balance/sync_cache_test.rb
@@ -0,0 +1,156 @@
+require "test_helper"
+
+class Balance::SyncCacheTest < ActiveSupport::TestCase
+  setup do
+    @family = families(:dylan_family)
+    @account = @family.accounts.create!(
+      name: "Test Account",
+      accountable: Depository.new,
+      currency: "USD",
+      balance: 1000
+    )
+  end
+
+  test "uses custom exchange rate from transaction extra field when present" do
+    # Create a transaction with EUR currency and custom exchange rate
+    _entry = @account.entries.create!(
+      date: Date.current,
+      name: "Test Transaction",
+      amount: 100,  # €100
+      currency: "EUR",
+      entryable: Transaction.new(
+        category: @family.categories.first,
+        extra: { "exchange_rate" => "1.5" }  # Custom rate: 1.5 (vs actual rate might be different)
+      )
+    )
+
+    sync_cache = Balance::SyncCache.new(@account)
+    converted_entries = sync_cache.send(:converted_entries)
+
+    converted_entry = converted_entries.first
+    assert_equal "USD", converted_entry.currency
+    assert_equal 150.0, converted_entry.amount  # 100 * 1.5 = 150
+  end
+
+  test "uses standard exchange rate lookup when custom rate not present" do
+    # Create an exchange rate in the database
+    ExchangeRate.create!(
+      from_currency: "EUR",
+      to_currency: "USD",
+      date: Date.current,
+      rate: 1.2
+    )
+
+    _entry = @account.entries.create!(
+      date: Date.current,
+      name: "Test Transaction",
+      amount: 100,  # €100
+      currency: "EUR",
+      entryable: Transaction.new(
+        category: @family.categories.first,
+        extra: {}  # No custom exchange rate
+      )
+    )
+
+    sync_cache = Balance::SyncCache.new(@account)
+    converted_entries = sync_cache.send(:converted_entries)
+
+    converted_entry = converted_entries.first
+    assert_equal "USD", converted_entry.currency
+    assert_equal 120.0, converted_entry.amount  # 100 * 1.2 = 120
+  end
+
+  test "converts multiple entries with correct rates" do
+    # Create exchange rates
+    ExchangeRate.create!(
+      from_currency: "EUR",
+      to_currency: "USD",
+      date: Date.current,
+      rate: 1.2
+    )
+    ExchangeRate.create!(
+      from_currency: "GBP",
+      to_currency: "USD",
+      date: Date.current,
+      rate: 1.27
+    )
+
+    # Create multiple entries in different currencies
+    _eur_entry = @account.entries.create!(
+      date: Date.current,
+      name: "EUR Transaction",
+      amount: 100,
+      currency: "EUR",
+      entryable: Transaction.new(
+        category: @family.categories.first,
+        extra: {}
+      )
+    )
+
+    _gbp_entry = @account.entries.create!(
+      date: Date.current,
+      name: "GBP Transaction",
+      amount: 50,
+      currency: "GBP",
+      entryable: Transaction.new(
+        category: @family.categories.first,
+        extra: {}
+      )
+    )
+
+    _usd_entry = @account.entries.create!(
+      date: Date.current,
+      name: "USD Transaction",
+      amount: 75,
+      currency: "USD",
+      entryable: Transaction.new(
+        category: @family.categories.first,
+        extra: {}
+      )
+    )
+
+    sync_cache = Balance::SyncCache.new(@account)
+    converted_entries = sync_cache.send(:converted_entries)
+
+    assert_equal 3, converted_entries.length
+
+    # All should be in USD
+    converted_entries.each { |e| assert_equal "USD", e.currency }
+
+    # Check converted amounts
+    # Sort amounts to check regardless of order
+    amounts = converted_entries.map(&:amount).sort
+    assert_in_delta 63.5, amounts[0], 0.01   # 50 GBP * 1.27
+    assert_in_delta 75.0, amounts[1], 0.01   # 75 USD * 1.0
+    assert_in_delta 120.0, amounts[2], 0.01  # 100 EUR * 1.2
+  end
+
+  test "prioritizes custom rate over fetched rate" do
+    # Create fetched rate
+    ExchangeRate.create!(
+      from_currency: "EUR",
+      to_currency: "USD",
+      date: Date.current,
+      rate: 1.2
+    )
+
+    # Create entry with custom rate that differs from fetched
+    _entry = @account.entries.create!(
+      date: Date.current,
+      name: "EUR Transaction with custom rate",
+      amount: 100,
+      currency: "EUR",
+      entryable: Transaction.new(
+        category: @family.categories.first,
+        extra: { "exchange_rate" => "1.5" }
+      )
+    )
+
+    sync_cache = Balance::SyncCache.new(@account)
+    converted_entries = sync_cache.send(:converted_entries)
+
+    converted_entry = converted_entries.first
+    # Should use custom rate (1.5), not fetched rate (1.2)
+    assert_equal 150.0, converted_entry.amount  # 100 * 1.5, not 100 * 1.2
+  end
+end
diff --git a/test/models/holding_test.rb b/test/models/holding_test.rb
index be58ed84f..39fdf6ac1 100644
--- a/test/models/holding_test.rb
+++ b/test/models/holding_test.rb
@@ -58,8 +58,9 @@ class HoldingTest < ActiveSupport::TestCase
     nvda_qty = BigDecimal("5") + BigDecimal("30")
     expected_nvda_usd = nvda_total_usd / nvda_qty
 
-    assert_equal Money.new(expected_amzn_usd, "CAD").exchange_to("USD", fallback_rate: 1), @amzn.avg_cost
-    assert_equal Money.new(expected_nvda_usd, "CAD").exchange_to("USD", fallback_rate: 1), @nvda.avg_cost
+    ExchangeRate.stubs(:find_or_fetch_rate).returns(OpenStruct.new(rate: 1))
+    assert_equal Money.new(expected_amzn_usd, "CAD").exchange_to("USD"), @amzn.avg_cost
+    assert_equal Money.new(expected_nvda_usd, "CAD").exchange_to("USD"), @nvda.avg_cost
   end
 
   test "calculates total return trend" do
diff --git a/test/models/transaction_test.rb b/test/models/transaction_test.rb
index 17018f778..e3fbf9c26 100644
--- a/test/models/transaction_test.rb
+++ b/test/models/transaction_test.rb
@@ -67,4 +67,64 @@ class TransactionTest < ActiveSupport::TestCase
     assert_includes Transaction::ACTIVITY_LABELS, "Exchange"
     assert_includes Transaction::ACTIVITY_LABELS, "Other"
   end
+
+  test "exchange_rate getter returns nil when extra is nil" do
+    transaction = Transaction.new
+    assert_nil transaction.exchange_rate
+  end
+
+  test "exchange_rate setter stores normalized numeric value" do
+    transaction = Transaction.new
+    transaction.exchange_rate = "1.5"
+
+    assert_equal 1.5, transaction.exchange_rate
+  end
+
+  test "exchange_rate setter marks invalid input" do
+    transaction = Transaction.new
+    transaction.exchange_rate = "not a number"
+
+    assert_equal "not a number", transaction.extra["exchange_rate"]
+    assert transaction.extra["exchange_rate_invalid"]
+  end
+
+  test "exchange_rate validation rejects non-numeric input" do
+    transaction = Transaction.new(
+      category: categories(:income),
+      extra: { "exchange_rate" => "invalid" }
+    )
+    transaction.exchange_rate = "not a number"
+
+    assert_not transaction.valid?
+    assert_includes transaction.errors[:exchange_rate], "must be a number"
+  end
+
+  test "exchange_rate validation rejects zero values" do
+    transaction = Transaction.new(
+      category: categories(:income)
+    )
+    transaction.exchange_rate = 0
+
+    assert_not transaction.valid?
+    assert_includes transaction.errors[:exchange_rate], "must be greater than 0"
+  end
+
+  test "exchange_rate validation rejects negative values" do
+    transaction = Transaction.new(
+      category: categories(:income)
+    )
+    transaction.exchange_rate = -1.5
+
+    assert_not transaction.valid?
+    assert_includes transaction.errors[:exchange_rate], "must be greater than 0"
+  end
+
+  test "exchange_rate validation allows positive values" do
+    transaction = Transaction.new(
+      category: categories(:income)
+    )
+    transaction.exchange_rate = 1.5
+
+    assert transaction.valid?
+  end
 end
diff --git a/test/models/transfer/creator_test.rb b/test/models/transfer/creator_test.rb
index a88a33a94..01a945999 100644
--- a/test/models/transfer/creator_test.rb
+++ b/test/models/transfer/creator_test.rb
@@ -218,4 +218,104 @@ class Transfer::CreatorTest < ActiveSupport::TestCase
       )
     end
   end
+
+  test "creates transfer with custom exchange rate when provided" do
+    # Create accounts with different currencies
+    usd_account = @family.accounts.create!(name: "USD Account", balance: 1000, currency: "USD", accountable: Depository.new)
+    eur_account = @family.accounts.create!(name: "EUR Account", balance: 1000, currency: "EUR", accountable: Depository.new)
+
+    custom_rate = 0.92 # 1 USD = 0.92 EUR
+    amount = 100
+
+    creator = Transfer::Creator.new(
+      family: @family,
+      source_account_id: usd_account.id,
+      destination_account_id: eur_account.id,
+      date: @date,
+      amount: amount,
+      exchange_rate: custom_rate
+    )
+
+    transfer = creator.create
+
+    assert transfer.persisted?
+
+    # Verify outflow transaction is in source currency
+    outflow = transfer.outflow_transaction
+    assert_equal amount, outflow.entry.amount
+    assert_equal "USD", outflow.entry.currency
+
+    # Verify inflow transaction uses custom exchange rate
+    inflow = transfer.inflow_transaction
+    expected_eur_amount = (amount * custom_rate * -1).round(2)
+    assert_in_delta expected_eur_amount, inflow.entry.amount, 0.01
+    assert_equal "EUR", inflow.entry.currency
+  end
+
+  test "falls back to fetched exchange rate when custom rate not provided" do
+    # Create accounts with different currencies
+    usd_account = @family.accounts.create!(name: "USD Account", balance: 1000, currency: "USD", accountable: Depository.new)
+    gbp_account = @family.accounts.create!(name: "GBP Account", balance: 1000, currency: "GBP", accountable: Depository.new)
+
+    # Mock the exchange rate lookup
+    ExchangeRate.expects(:find_or_fetch_rate)
+                .with(from: "USD", to: "GBP", date: @date)
+                .returns(OpenStruct.new(rate: 0.79))
+
+    creator = Transfer::Creator.new(
+      family: @family,
+      source_account_id: usd_account.id,
+      destination_account_id: gbp_account.id,
+      date: @date,
+      amount: 100
+    )
+
+    transfer = creator.create
+
+    assert transfer.persisted?
+    assert_equal "USD", transfer.outflow_transaction.entry.currency
+    assert_equal "GBP", transfer.inflow_transaction.entry.currency
+  end
+
+  test "raises when no exchange rate available and none provided" do
+    # Create accounts with different currencies
+    usd_account = @family.accounts.create!(name: "USD Account", balance: 1000, currency: "USD", accountable: Depository.new)
+    jpy_account = @family.accounts.create!(name: "JPY Account", balance: 100000, currency: "JPY", accountable: Depository.new)
+
+    # Mock no exchange rate found
+    ExchangeRate.expects(:find_or_fetch_rate)
+                .with(from: "USD", to: "JPY", date: @date)
+                .returns(nil)
+
+    creator = Transfer::Creator.new(
+      family: @family,
+      source_account_id: usd_account.id,
+      destination_account_id: jpy_account.id,
+      date: @date,
+      amount: 100
+    )
+
+    assert_raises(Money::ConversionError) do
+      creator.create
+    end
+  end
+
+  test "custom exchange rate with very small value is valid" do
+    usd_account = @family.accounts.create!(name: "USD Account", balance: 1000, currency: "USD", accountable: Depository.new)
+    eur_account = @family.accounts.create!(name: "EUR Account", balance: 1000, currency: "EUR", accountable: Depository.new)
+
+    creator = Transfer::Creator.new(
+      family: @family,
+      source_account_id: usd_account.id,
+      destination_account_id: eur_account.id,
+      date: @date,
+      amount: 100,
+      exchange_rate: 0.000001
+    )
+
+    transfer = creator.create
+
+    assert transfer.persisted?
+    assert_in_delta(-0.0001, transfer.inflow_transaction.entry.amount, 0.0001)
+  end
 end
diff --git a/test/system/transactions_form_exchange_rate_test.rb b/test/system/transactions_form_exchange_rate_test.rb
new file mode 100644
index 000000000..4e611e881
--- /dev/null
+++ b/test/system/transactions_form_exchange_rate_test.rb
@@ -0,0 +1,146 @@
+require "application_system_test_case"
+
+class TransactionsFormExchangeRateTest < ApplicationSystemTestCase
+  setup do
+    @user = users(:family_admin)
+    @family = @user.family
+    @account_usd = accounts(:depository) # USD account
+    sign_in @user
+
+    # Set up real exchange rates for testing
+    @eur_usd_rate = ExchangeRate.create!(
+      from_currency: "EUR",
+      to_currency: "USD",
+      date: Date.current,
+      rate: 1.1
+    )
+
+    @gbp_usd_rate = ExchangeRate.create!(
+      from_currency: "GBP",
+      to_currency: "USD",
+      date: Date.current,
+      rate: 1.27
+    )
+  end
+
+  test "changing amount currency to different currency shows exchange rate UI" do
+    visit new_transaction_path
+
+    # Select USD account (which is in USD)
+    select_ds("Account", @account_usd)
+
+    # Currency defaults to USD (same as account)
+    # Change currency to EUR
+    find("select[data-money-field-target='currency']").find("option[value='EUR']").select_option
+
+    # Exchange rate UI should appear
+    assert_selector "[data-transaction-form-target='exchangeRateContainer']", visible: true
+  end
+
+  test "changing amount currency to same as account currency hides exchange rate UI" do
+    visit new_transaction_path
+
+    # Select USD account
+    select_ds("Account", @account_usd)
+
+    # Change to EUR first
+    find("select[data-money-field-target='currency']").find("option[value='EUR']").select_option
+
+    # Verify exchange rate UI is shown
+    assert_selector "[data-transaction-form-target='exchangeRateContainer']", visible: true
+
+    # Change back to USD (same as account)
+    find("select[data-money-field-target='currency']").find("option[value='USD']").select_option
+
+    # Exchange rate UI should hide
+    assert_selector "[data-transaction-form-target='exchangeRateContainer']", visible: false
+  end
+
+  test "exchange rate field is prefilled when rate is available" do
+    visit new_transaction_path
+
+    # Select USD account
+    select_ds("Account", @account_usd)
+
+    # Change to GBP (exchange rate is set up in fixtures)
+    find("select[data-money-field-target='currency']").find("option[value='GBP']").select_option
+
+    # Wait for exchange rate container to become visible
+    assert_selector "[data-transaction-form-target='exchangeRateContainer']", visible: true
+
+    # Exchange rate field should be populated
+    exchange_rate_field = find("[data-transaction-form-target='exchangeRateField']")
+    assert_not_empty exchange_rate_field.value
+    assert_equal "1.27", exchange_rate_field.value
+  end
+
+  test "exchange rate field is empty when rate not found" do
+    visit new_transaction_path
+
+    # Select USD account
+    select_ds("Account", @account_usd)
+
+    # Change to CHF (Swiss Franc - no rate set up in fixtures)
+    find("select[data-money-field-target='currency']").find("option[value='CHF']").select_option
+
+    # Wait for exchange rate container to become visible (manual rate entry mode)
+    assert_selector "[data-transaction-form-target='exchangeRateContainer']", visible: true
+
+    # Exchange rate section should be visible but field should be empty (manual entry)
+    exchange_rate_field = find("[data-transaction-form-target='exchangeRateField']")
+    assert_empty exchange_rate_field.value
+  end
+
+  test "exchange rate is recalculated when currency changes" do
+    visit new_transaction_path
+
+    # Select USD account
+    select_ds("Account", @account_usd)
+
+    # Change to EUR
+    find("select[data-money-field-target='currency']").find("option[value='EUR']").select_option
+
+    # Wait for EUR rate to load
+    assert_selector "[data-transaction-form-target='exchangeRateContainer']", visible: true
+    first_rate = find("[data-transaction-form-target='exchangeRateField']").value
+    assert_equal "1.10", first_rate
+
+    # Change to GBP
+    find("select[data-money-field-target='currency']").find("option[value='GBP']").select_option
+
+    # Wait for GBP rate to be updated
+    assert_selector "[data-transaction-form-target='exchangeRateContainer']", visible: true
+    second_rate = find("[data-transaction-form-target='exchangeRateField']").value
+    assert_equal "1.27", second_rate
+
+    # Rates should be different
+    assert_not_equal first_rate, second_rate
+  end
+
+  test "changing account also recalculates exchange rate for current currency" do
+    # Create a second account in EUR
+    eur_account = @family.accounts.create!(
+      name: "EUR Account",
+      balance: 1000,
+      currency: "EUR",
+      accountable: Depository.new
+    )
+
+    visit new_transaction_path
+
+    # Start with USD account, then currency EUR
+    select_ds("Account", @account_usd)
+
+    find("select[data-money-field-target='currency']").find("option[value='EUR']").select_option
+
+    # Exchange rate shown (both USD and EUR exist, they differ)
+    assert_selector "[data-transaction-form-target='exchangeRateContainer']", visible: true
+
+    # Switch to EUR account
+    select_ds("Account", eur_account)
+
+    # Now account is EUR and currency is EUR (same)
+    # Exchange rate UI should hide
+    assert_selector "[data-transaction-form-target='exchangeRateContainer']", visible: false
+  end
+end
diff --git a/test/system/transfers_test.rb b/test/system/transfers_test.rb
index 6fbd81928..a849a401c 100644
--- a/test/system/transfers_test.rb
+++ b/test/system/transfers_test.rb
@@ -27,6 +27,58 @@ class TransfersTest < ApplicationSystemTestCase
     end
   end
 
+  test "shows exchange rate field for different currencies" do
+    # Create an account with a different currency
+    eur_account = @user.family.accounts.create!(
+      name: "EUR Savings",
+      balance: 1000,
+      currency: "EUR",
+      accountable: Depository.new
+    )
+
+    # Set up exchange rate
+    ExchangeRate.create!(
+      from_currency: "USD",
+      to_currency: "EUR",
+      date: Date.current,
+      rate: 0.92
+    )
+
+    transfer_date = Date.current
+
+    click_on "New transaction"
+    click_on "Transfer"
+    assert_text "New transfer"
+
+    # Initially, exchange rate field should be hidden
+    assert_selector "[data-transfer-form-target='exchangeRateContainer'].hidden", visible: :all
+
+    # Select accounts with different currencies
+    select_ds("From", accounts(:depository))
+    select_ds("To", eur_account)
+
+    # Exchange rate container should become visible
+    assert_selector "[data-transfer-form-target='exchangeRateContainer']", visible: true
+
+    # Exchange rate field should be populated with fetched rate
+    exchange_rate_field = find("[data-transfer-form-target='exchangeRateField']")
+    assert_not_empty exchange_rate_field.value
+    assert_equal "0.92", exchange_rate_field.value
+
+    # Fill in amount
+    fill_in "transfer[amount]", with: 100
+    fill_in "Date", with: transfer_date
+
+    # Submit form
+    click_button "Create transfer"
+
+    # Should redirect and show transfer created
+    assert_current_path transactions_url
+    within "#entry-group-#{transfer_date}" do
+      assert_text "Transfer to"
+    end
+  end
+
   private
 
     def select_ds(label_text, record)