feat(budgets): add per-user personal budgets with strict isolation (#2891)

* feat(budgets): add per-user personal budgets with strict isolation

Families can now opt into personal budgets (toggleable via family
settings): each family member gets their own budget for a given
period instead of sharing a single family-wide budget.

- Add families.personal_budgets flag and budgets.user_id, with
  partial unique indexes so shared budgets (user_id IS NULL) and
  personal budgets (user_id IS NOT NULL) can't collide.
- Budget.find_or_bootstrap scopes lookup/creation by user when the
  family has personal_budgets enabled.
- Scope most_recent_initialized_budget (used to seed a new budget
  from the prior period) by user_id so one user's copy-forward never
  bleeds into another user's budget.
- budgets.user_id cascades on user deletion so personal budgets don't
  outlive their owner.

* feat(budgets): enforce user-specific budget ownership and cascade deletion

* feat(budgets): display user name for personal budgets in budget card on the plan section

* feat(budgets): enhance personal budgets display for admins with preview feature indication

* feat(budgets): enforce user-specific budget and category visibility for personal budgets

* feat(budgets): create budget section titles and add translations notice in preferences

* feat(budgets): let household and personal budgets coexist with sharing

Previously enabling personal_budgets made the shared household budget
unreachable. Budget.find_or_bootstrap now takes an explicit household:
flag so both can be resolved independently for the same period, with a
new household_budget_enabled family setting to opt out of the household
side and keep personal budgets only.

Adds a BudgetShare model (read_only/read_write) so a member can grant
another family member access to their personal budget, enforced via
Budget#viewable_by?/editable_by? across BudgetsController,
BudgetCategoriesController, PlansController, and the read-only API.
Preferences gains a Budget sharing card (gated on preview access like
the rest of the personal budgets UI) and an owner switcher pill (
Household / mine / shared-with-me) appears on the budget page and the
Plan hub card.

Also fixes personal budgets showing the same "actual spending" as the
household budget: actual spending/income now scope to the budget
owner's own accounts instead of the viewer's full accessible set,
via a new accounts: override on IncomeStatement.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

* feat(budgets): enhance budget switcher with icons and improved styling

* feat(budgets): remove user name display from budget card and header

* feat(budgets): remove unique index on taggable_type and taggable_id in taggings

* feat(budgets): enhance budget sharing functionality and improve UI elements

* Collapse personal budget migrations

---------

Signed-off-by: JulienGourmet <69808509+jubbakka@users.noreply.github.com>
Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>
Co-authored-by: sure-admin <sure-admin@splashblot.com>

Gemfile

@@ -75,7 +75,7 @@ gem "octokit"
 gem "pagy"
 gem "rails-i18n"
 gem "rails-settings-cached"
-gem "tzinfo-data", platforms: %i[windows jruby]
+gem "tzinfo-data", platforms: %i[mswin mswin64 mingw x64_mingw jruby]
 gem "csv"
 gem "rchardet" # Character encoding detection
 gem "redcarpet"
@@ -107,7 +107,7 @@ gem "anthropic", "~> 1.0"
 gem "langfuse-ruby", "~> 0.1.4", require: "langfuse"
 
 group :development, :test do
-  gem "debug", platforms: %i[mri windows]
+  gem "debug", platforms: %i[mri mswin mswin64 mingw x64_mingw]
   gem "brakeman", require: false
   gem "rubocop-rails-omakase", require: false
   gem "i18n-tasks"

app/controllers/api/v1/budget_categories_controller.rb

@@ -39,10 +39,15 @@ class Api::V1::BudgetCategoriesController < Api::V1::BaseController
     def budget_categories_scope
       BudgetCategory
         .joins(:budget, :category)
-        .where(budgets: { family_id: current_resource_owner.family_id })
+        .where(budgets: { family_id: current_resource_owner.family_id, user_id: visible_owner_ids })
         .includes({ budget: { budget_categories: { category: :parent } } }, category: :parent)
     end
 
+    def visible_owner_ids
+      shared_with_me = BudgetShare.where(viewer_id: current_resource_owner.id).pluck(:owner_id)
+      [ nil, current_resource_owner.id, *shared_with_me ]
+    end
+
     def apply_filters(query)
       if params[:budget_id].present?
         raise InvalidFilterError, "budget_id must be a valid UUID" unless valid_uuid?(params[:budget_id])

app/controllers/api/v1/budgets_controller.rb

@@ -42,6 +42,16 @@ class Api::V1::BudgetsController < Api::V1::BaseController
     end
 
     def budgets_scope
-      current_resource_owner.family.budgets.includes(budget_categories: :category)
+      current_resource_owner.family.budgets
+        .where(user_id: visible_owner_ids)
+        .includes(budget_categories: :category)
+    end
+
+    # nil (the shared household budget) + the caller's own personal budget +
+    # any owner who granted the caller a BudgetShare (read-only or
+    # read-write — this API is read-only either way).
+    def visible_owner_ids
+      shared_with_me = BudgetShare.where(viewer_id: current_resource_owner.id).pluck(:owner_id)
+      [ nil, current_resource_owner.id, *shared_with_me ]
     end
 end

app/controllers/budget_categories_controller.rb

@@ -1,5 +1,8 @@
 class BudgetCategoriesController < ApplicationController
+  include BudgetOwnership
+
   before_action :set_budget
+  before_action :ensure_budget_editable!, only: %i[index update]
 
   def index
     @budget_categories = @budget.budget_categories.includes(:category)
@@ -21,7 +24,7 @@ class BudgetCategoriesController < ApplicationController
       @budget_category = @budget.uncategorized_budget_category
       @recent_transactions = @recent_transactions.where(transactions: { category_id: nil })
     else
-      @budget_category = Current.family.budget_categories.find(params[:id])
+      @budget_category = @budget.budget_categories.find(params[:id])
       @recent_transactions = @recent_transactions.joins("LEFT JOIN categories ON categories.id = transactions.category_id")
                                                  .where("categories.id = ? OR categories.parent_id = ?", @budget_category.category.id, @budget_category.category.id)
     end
@@ -30,12 +33,12 @@ class BudgetCategoriesController < ApplicationController
   end
 
   def update
-    @budget_category = Current.family.budget_categories.find(params[:id])
+    @budget_category = @budget.budget_categories.find(params[:id])
     @budget_category.update_budgeted_spending!(budgeted_spending_param)
 
     respond_to do |format|
       format.turbo_stream
-      format.html { redirect_to budget_budget_categories_path(@budget) }
+      format.html { redirect_to budget_budget_categories_path(@budget, **budget_owner_query) }
     end
   rescue ActiveRecord::RecordInvalid
     render :index, status: :unprocessable_entity
@@ -51,6 +54,7 @@ class BudgetCategoriesController < ApplicationController
 
     def set_budget
       start_date = Budget.param_to_date(params[:budget_month_year], family: Current.family)
-      @budget = Current.family.budgets.find_by!(start_date: start_date)
+      @budget = resolve_budget(start_date)
+      raise ActiveRecord::RecordNotFound unless @budget
     end
 end

app/controllers/budgets_controller.rb

@@ -1,5 +1,8 @@
 class BudgetsController < ApplicationController
+  include BudgetOwnership
+
   before_action :set_budget, only: %i[show edit update copy_previous]
+  before_action :ensure_budget_editable!, only: %i[edit update copy_previous]
 
   def index
     redirect_to_current_month_budget
@@ -7,6 +10,8 @@ class BudgetsController < ApplicationController
 
   def show
     @source_budget = @budget.most_recent_initialized_budget unless @budget.initialized?
+    @editable = @budget.editable_by?(Current.user)
+    @switch_options = budget_switch_options(@budget)
     @breadcrumbs = plan_breadcrumb_prefix + [ [ t("breadcrumbs.budgets"), nil ] ]
   end
 
@@ -16,12 +21,12 @@ class BudgetsController < ApplicationController
 
   def update
     @budget.update!(budget_params)
-    redirect_to budget_budget_categories_path(@budget)
+    redirect_to budget_budget_categories_path(@budget, **budget_owner_query)
   end
 
   def copy_previous
     if @budget.initialized?
-      redirect_to budget_path(@budget), alert: t("budgets.copy_previous.already_initialized")
+      redirect_to budget_path(@budget, **budget_owner_query), alert: t("budgets.copy_previous.already_initialized")
       return
     end
 
@@ -29,9 +34,9 @@ class BudgetsController < ApplicationController
 
     if source_budget
       @budget.copy_from!(source_budget)
-      redirect_to budget_budget_categories_path(@budget), notice: t("budgets.copy_previous.success", source_name: source_budget.name)
+      redirect_to budget_budget_categories_path(@budget, **budget_owner_query), notice: t("budgets.copy_previous.success", source_name: source_budget.name)
     else
-      redirect_to budget_path(@budget), alert: t("budgets.copy_previous.no_source")
+      redirect_to budget_path(@budget, **budget_owner_query), alert: t("budgets.copy_previous.no_source")
     end
   end
 
@@ -54,12 +59,12 @@ class BudgetsController < ApplicationController
 
     def set_budget
       start_date = Budget.param_to_date(params[:month_year], family: Current.family)
-      @budget = Budget.find_or_bootstrap(Current.family, start_date: start_date, user: Current.user)
+      @budget = resolve_budget(start_date)
       raise ActiveRecord::RecordNotFound unless @budget
     end
 
     def redirect_to_current_month_budget
-      current_budget = Budget.find_or_bootstrap(Current.family, start_date: Date.current, user: Current.user)
-      redirect_to budget_path(current_budget)
+      current_budget = resolve_budget(Date.current)
+      redirect_to budget_path(current_budget, **budget_owner_query)
     end
 end

app/controllers/concerns/budget_ownership.rb

@@ -0,0 +1,107 @@
+# Resolves "whose budget is this request about" from the `owner` query
+# param, shared by BudgetsController, BudgetCategoriesController, and
+# PlansController now that a household budget and personal budgets can
+# coexist. `owner` is either "household", a user id, or absent (defaults to
+# the signed-in user's own budget).
+module BudgetOwnership
+  extend ActiveSupport::Concern
+
+  # budget_owner_query lives in BudgetsHelper (not defined here) so it's
+  # usable both from controller redirects (via this include) and from any
+  # view context, including isolated partial/view tests.
+  included do
+    include BudgetsHelper
+  end
+
+  private
+    def viewing_household_budget?
+      params[:owner] == "household"
+    end
+
+    # Falls back to Current.user whenever the requested owner can't be
+    # resolved or isn't shared with the signed-in user, rather than raising
+    # — worst case the request just shows the viewer their own budget.
+    def budget_target_user
+      return Current.user if params[:owner].blank? || viewing_household_budget?
+
+      candidate = Current.family.users.find_by(id: params[:owner])
+      return Current.user if candidate.nil? || candidate.id == Current.user.id
+      return candidate if BudgetShare.exists?(owner_id: candidate.id, viewer_id: Current.user.id)
+
+      Current.user
+    end
+
+    def resolve_budget(start_date)
+      target_user = budget_target_user
+
+      if target_user != Current.user
+        # Viewing another family member's shared budget: resolve an existing
+        # budget for that period without creating one on their behalf — a
+        # mere page view shouldn't vivify a row in someone else's budget
+        # history. Falls back to the viewer's own budget (auto-created) when
+        # the owner hasn't set one up yet, same as the household fallback
+        # below, so shared-budget navigation doesn't dead-end.
+        budget_start, budget_end = Budget.period_for(start_date, family: Current.family)
+        existing = Current.family.budgets.find_by(start_date: budget_start, end_date: budget_end, user: target_user)
+        return existing if existing
+
+        return Budget.find_or_bootstrap(Current.family, start_date: start_date, user: Current.user, household: false)
+      end
+
+      budget = Budget.find_or_bootstrap(
+        Current.family,
+        start_date: start_date,
+        user: target_user,
+        household: viewing_household_budget?
+      )
+
+      return budget if budget || !viewing_household_budget?
+
+      # Household budget was explicitly requested but the family disabled it
+      # (stale link, bookmarked URL) — fall back to the viewer's own budget
+      # rather than a hard 404.
+      Budget.find_or_bootstrap(Current.family, start_date: start_date, user: Current.user, household: false)
+    end
+
+    def ensure_budget_editable!
+      raise ActiveRecord::RecordNotFound unless @budget.editable_by?(Current.user)
+    end
+
+    # Pills for the household/personal budget switcher. Empty (no switcher)
+    # unless personal_budgets is on — families that never turned it on keep
+    # the single, switcher-less budget page they've always had. Household
+    # gets a people icon; every person (the viewer included) gets a
+    # colored initial avatar, so all three read as "who" at a glance.
+    def budget_switch_options(budget)
+      return [] unless Current.family.personal_budgets?
+
+      options = []
+
+      if Current.family.household_budget_enabled?
+        options << {
+          label: t("budgets.switcher.household"),
+          icon: "users",
+          owner_param: "household",
+          active: budget.user_id.nil?
+        }
+      end
+
+      options << {
+        label: Current.user.display_name,
+        icon: nil,
+        owner_param: Current.user.id,
+        active: budget.user_id == Current.user.id
+      }
+
+      Current.user.budget_owners_shared_with_me.find_each do |owner|
+        options << {
+          label: owner.display_name,
+          icon: nil,
+          owner_param: owner.id,
+          active: budget.user_id == owner.id
+        }
+      end
+
+      options
+    end
+end

app/controllers/plans_controller.rb

@@ -1,4 +1,6 @@
 class PlansController < ApplicationController
+  include BudgetOwnership
+
   # The Plan hub fronts budgets + goals under one nav entry, and only
   # replaces the Budgets entry for preview users (see
   # ApplicationHelper#plan_nav_item). Without the flag, fall through to the
@@ -6,7 +8,9 @@ class PlansController < ApplicationController
   before_action :redirect_to_budgets_unless_preview
 
   def show
-    @budget = Budget.find_or_bootstrap(Current.family, start_date: Date.current, user: Current.user)
+    @budget = resolve_budget(Date.current)
+    @editable = @budget.editable_by?(Current.user)
+    @switch_options = budget_switch_options(@budget)
     @top_budget_categories = @budget.initialized? ? @budget.top_spending_categories : []
 
     @goals = Goal.active_prepared_for(Current.family)

app/controllers/settings/budget_shares_controller.rb

@@ -0,0 +1,40 @@
+class Settings::BudgetSharesController < ApplicationController
+  layout "settings"
+
+  def update
+    eligible_members = Current.family.users.where.not(id: Current.user.id).where(active: true)
+
+    BudgetShare.transaction do
+      sharing_members_params.each do |member_params|
+        viewer = eligible_members.find_by(id: member_params[:viewer_id])
+        next unless viewer
+
+        share = Current.user.budget_shares_given.find_by(viewer: viewer)
+        permission = member_params[:permission].presence
+
+        if permission.in?(BudgetShare::PERMISSIONS)
+          if share
+            share.update!(permission: permission)
+          else
+            Current.user.budget_shares_given.create!(viewer: viewer, permission: permission)
+          end
+        elsif share
+          share.destroy!
+        end
+      end
+    end
+
+    redirect_to settings_preferences_path, notice: t(".success")
+  end
+
+  private
+    def sharing_members_params
+      return [] unless params.dig(:budget_shares, :members)
+
+      members = params.require(:budget_shares).permit(
+        members: [ :viewer_id, :permission ]
+      )[:members]
+
+      members.is_a?(Array) ? members : members&.values || []
+    end
+end

app/controllers/settings/preferences_controller.rb

@@ -3,6 +3,8 @@ class Settings::PreferencesController < ApplicationController
 
   def show
     @user = Current.user
+    @family_members = Current.family.users.where.not(id: @user.id).where(active: true)
+    @budget_shares = @user.budget_shares_given.index_by(&:viewer_id)
   end
 
   # Writes per-user boolean preferences stored in the JSONB `users.preferences`

app/controllers/users_controller.rb

@@ -114,6 +114,7 @@ class UsersController < ApplicationController
     def user_params
       family_attrs = [ :name, :currency, :country, :date_format, :timezone, :locale, :month_start_day, :id ]
       if Current.user.admin?
+        family_attrs.push(:personal_budgets, :household_budget_enabled) # Needed for updating existing family
         family_attrs.push(:moniker, :default_account_sharing)
         family_attrs << { enabled_currencies: [] }
       end
@@ -137,8 +138,10 @@ class UsersController < ApplicationController
       moniker_changed = family_attrs[:moniker].present? && family_attrs[:moniker] != Current.family.moniker
       sharing_changed = family_attrs[:default_account_sharing].present? && family_attrs[:default_account_sharing] != Current.family.default_account_sharing
       enabled_currencies_changed = family_attrs.key?(:enabled_currencies)
+      personal_budgets_changed = family_attrs.key?(:personal_budgets)
+      household_budget_enabled_changed = family_attrs.key?(:household_budget_enabled)
 
-      moniker_changed || sharing_changed || enabled_currencies_changed
+      moniker_changed || sharing_changed || enabled_currencies_changed || personal_budgets_changed || household_budget_enabled_changed
     end
 
     def ensure_admin

app/helpers/budgets_helper.rb

@@ -1,4 +1,15 @@
 module BudgetsHelper
+  # Forwards the current `owner` param (if any) so links generated while
+  # viewing the household budget or a shared member's budget keep pointing
+  # at that same budget instead of silently resetting to "mine". Defined
+  # here (rather than only in BudgetOwnership) so it's available to any view
+  # context, including isolated view tests that render budget partials
+  # without a full BudgetsController/BudgetCategoriesController/
+  # PlansController request cycle.
+  def budget_owner_query
+    params[:owner].present? ? { owner: params[:owner] } : {}
+  end
+
   def budget_has_over_budget?(budget)
     return false unless budget.initialized?
 

app/models/assistant/function/get_budget.rb

@@ -88,7 +88,11 @@ class Assistant::Function::GetBudget < Assistant::Function
         Budget.find_or_bootstrap(family, start_date: start_date, user: user)
       else
         budget_start, budget_end = Budget.period_for(start_date, family: family)
-        family.budgets.find_by(start_date: budget_start, end_date: budget_end)
+        family.budgets.find_by(
+          start_date: budget_start,
+          end_date: budget_end,
+          user: family.personal_budgets? ? user : nil
+        )
       end
       return nil unless budget
 

app/models/budget.rb

@@ -6,11 +6,12 @@ class Budget < ApplicationRecord
   attr_accessor :current_user
 
   belongs_to :family
+  belongs_to :user, optional: true
 
   has_many :budget_categories, -> { includes(:category) }, dependent: :destroy
 
   validates :start_date, :end_date, presence: true
-  validates :start_date, :end_date, uniqueness: { scope: :family_id }
+  validates :start_date, :end_date, uniqueness: { scope: [ :family_id, :user_id ] }
 
   monetize :budgeted_spending, :expected_income, :allocated_spending,
            :actual_spending, :available_to_spend, :available_to_allocate,
@@ -44,16 +45,29 @@ class Budget < ApplicationRecord
       end
     end
 
-    def find_or_bootstrap(family, start_date:, user: nil)
+    # `household: true` explicitly requests the shared household budget
+    # (user_id NULL) regardless of `user:` — this is what lets a household
+    # budget and personal budgets coexist once `family.personal_budgets?` is
+    # on. Without it, `user:` resolves to that user's personal budget when
+    # personal_budgets is on, or the shared budget otherwise (unchanged
+    # behavior for families that never turned personal budgets on).
+    #
+    # Returns nil if the household budget was explicitly requested but the
+    # family opted out of it via `household_budget_enabled?`.
+    def find_or_bootstrap(family, start_date:, user: nil, household: false)
       return nil unless budget_date_valid?(start_date, family: family)
+      return nil if household && family.personal_budgets? && !family.household_budget_enabled?
 
       Budget.transaction do
         budget_start, budget_end = period_for(start_date, family: family)
 
+        owner = (household || !family.personal_budgets?) ? nil : user
+
         budget = Budget.find_or_create_by!(
           family: family,
           start_date: budget_start,
-          end_date: budget_end
+          end_date: budget_end,
+          user: owner
         ) do |b|
           b.currency = family.currency
         end
@@ -117,11 +131,20 @@ class Budget < ApplicationRecord
     end
   end
 
+  # Personal budgets only ever reflect the owner's own accounts, regardless
+  # of who's viewing (a shared read-only/read-write viewer sees the owner's
+  # numbers, not their own accessible accounts). The household budget keeps
+  # the pre-personal-budgets behavior: whatever the requesting viewer can
+  # see, since it has no single owner to scope by.
   def transactions
     scope = family.transactions.visible.in_period(period)
-    if current_user
+
+    if user_id.present?
+      scope = scope.joins(:entry).where(entries: { account_id: family.accounts.where(owner_id: user_id).included_in_reports.select(:id) })
+    elsif current_user
       scope = scope.joins(:entry).where(entries: { account_id: family.accounts.accessible_by(current_user).included_in_reports.select(:id) })
     end
+
     scope
   end
 
@@ -141,17 +164,37 @@ class Budget < ApplicationRecord
     budgeted_spending.present?
   end
 
+  # The household budget (user_id nil) is visible/editable by every family
+  # member, matching pre-personal_budgets behavior. A personal budget is
+  # only visible/editable by its owner, or by someone the owner shared it
+  # with via BudgetShare.
+  def viewable_by?(user)
+    return true if user_id.nil?
+    return true if user_id == user.id
+
+    BudgetShare.exists?(owner_id: user_id, viewer_id: user.id)
+  end
+
+  def editable_by?(user)
+    return true if user_id.nil?
+    return true if user_id == user.id
+
+    BudgetShare.exists?(owner_id: user_id, viewer_id: user.id, permission: "read_write")
+  end
+
   def most_recent_initialized_budget
     family.budgets
       .includes(:budget_categories)
       .where("start_date < ?", start_date)
       .where.not(budgeted_spending: nil)
+      .where(user_id: user_id)
       .order(start_date: :desc)
       .first
   end
 
   def copy_from!(source_budget)
     raise ArgumentError, "source budget must belong to the same family" unless source_budget.family_id == family_id
+    raise ArgumentError, "source budget must belong to the same user" unless source_budget.user_id == user_id
     raise ArgumentError, "source budget must precede target budget" unless source_budget.start_date < start_date
 
     Budget.transaction do
@@ -316,11 +359,11 @@ class Budget < ApplicationRecord
   # Income: How much user earned relative to what they expected to earn
   # =============================================================================
   def estimated_income
-    family.income_statement.median_income(interval: "month")
+    income_statement.median_income(interval: "month")
   end
 
   def actual_income
-    family.income_statement.income_totals(period: self.period).total
+    income_statement.income_totals(period: self.period).total
   end
 
   def actual_income_percent
@@ -341,7 +384,16 @@ class Budget < ApplicationRecord
 
   private
     def income_statement
-      @income_statement ||= family.income_statement(user: current_user)
+      @income_statement ||= family.income_statement(user: current_user, accounts: income_statement_accounts)
+    end
+
+    # nil for the household budget (IncomeStatement falls back to whatever
+    # `current_user` can see, unchanged pre-personal-budgets behavior). For a
+    # personal budget, restrict to the owner's own accounts so a shared
+    # viewer sees the owner's numbers, and household vs. personal actually
+    # differ instead of both reflecting the viewer's full accessible set.
+    def income_statement_accounts
+      family.accounts.where(owner_id: user_id).included_in_reports if user_id.present?
     end
 
     def net_totals

app/models/budget_share.rb

@@ -0,0 +1,30 @@
+class BudgetShare < ApplicationRecord
+  belongs_to :owner, class_name: "User"
+  belongs_to :viewer, class_name: "User"
+
+  PERMISSIONS = %w[read_write read_only].freeze
+
+  validates :permission, inclusion: { in: PERMISSIONS }
+  validates :viewer_id, uniqueness: { scope: :owner_id }
+  validate :cannot_share_with_self
+  validate :owner_and_viewer_in_same_family
+
+  def read_write?
+    permission == "read_write"
+  end
+
+  def read_only?
+    permission == "read_only"
+  end
+
+  private
+    def cannot_share_with_self
+      errors.add(:viewer, "can't be the owner") if owner_id.present? && owner_id == viewer_id
+    end
+
+    def owner_and_viewer_in_same_family
+      if owner && viewer && owner.family_id != viewer.family_id
+        errors.add(:viewer, "must be in the same family")
+      end
+    end
+end

app/models/family.rb

@@ -144,6 +144,8 @@ class Family < ApplicationRecord
   validates :moniker, inclusion: { in: MONIKERS }
   validates :assistant_type, inclusion: { in: ASSISTANT_TYPES }
   validates :default_account_sharing, inclusion: { in: SHARING_DEFAULTS }
+  validates :personal_budgets, inclusion: { in: [ true, false ] }
+  validates :household_budget_enabled, inclusion: { in: [ true, false ] }
   validate :timezone_must_be_a_known_zone, if: :timezone_changed?
 
   before_validation :normalize_enabled_currencies!
@@ -311,8 +313,8 @@ class Family < ApplicationRecord
     BalanceSheet.new(self, user: user)
   end
 
-  def income_statement(user: Current.user)
-    IncomeStatement.new(self, user: user)
+  def income_statement(user: Current.user, accounts: nil)
+    IncomeStatement.new(self, user: user, accounts: accounts)
   end
 
   # Returns the Investment Contributions category for this family, creating it if it doesn't exist.

app/models/income_statement.rb

@@ -7,9 +7,14 @@ class IncomeStatement
 
   attr_reader :family, :user
 
-  def initialize(family, user: nil)
+  # `accounts:` overrides the account scope entirely (e.g. a personal
+  # budget's "owned accounts only" view) instead of inferring it from
+  # `user.finance_accounts`. `user` is still kept for cache-key/estimate
+  # purposes when both are given.
+  def initialize(family, user: nil, accounts: nil)
     @family = family
     @user = user || Current.user
+    @accounts = accounts
   end
 
   def totals(transactions_scope: nil, date_range:)
@@ -239,7 +244,11 @@ class IncomeStatement
     end
 
     def included_account_ids
-      @included_account_ids ||= user ? user.finance_accounts.pluck(:id) : nil
+      @included_account_ids ||= if @accounts
+        @accounts.pluck(:id)
+      elsif user
+        user.finance_accounts.pluck(:id)
+      end
     end
 
     def included_account_ids_hash

app/models/user.rb

@@ -35,6 +35,8 @@ class User < ApplicationRecord
   has_many :owned_accounts, class_name: "Account", foreign_key: :owner_id
   has_many :account_shares, dependent: :destroy
   has_many :shared_accounts, through: :account_shares, source: :account
+  has_many :budget_shares_given, class_name: "BudgetShare", foreign_key: :owner_id, inverse_of: :owner, dependent: :destroy
+  has_many :budget_shares_received, class_name: "BudgetShare", foreign_key: :viewer_id, inverse_of: :viewer, dependent: :destroy
   accepts_nested_attributes_for :family, update_only: true
 
   MFA_BACKUP_CODE_COUNT = 8
@@ -156,6 +158,12 @@ class User < ApplicationRecord
     family.accounts.included_in_finances_for(self)
   end
 
+  # Other family members who have granted this user access to their personal
+  # budget (see BudgetShare). Used to build the budget owner switcher.
+  def budget_owners_shared_with_me
+    User.where(id: budget_shares_received.select(:owner_id))
+  end
+
   def display_name
     [ first_name, last_name ].compact.join(" ").presence || email
   end

app/views/budget_categories/_budget_category.html.erb

@@ -3,7 +3,7 @@
 <% category_display_name = budget_category.category.display_name %>
 
 <%= turbo_frame_tag dom_id(budget_category), class: "flex-1 min-w-0 block" do %>
-  <%= link_to budget_budget_category_path(budget_category.budget, budget_category), class: "group block w-full px-4 py-2 bg-container", data: { turbo_frame: "drawer" } do %>
+  <%= link_to budget_budget_category_path(budget_category.budget, budget_category, **budget_owner_query), class: "group block w-full px-4 py-2 bg-container", data: { turbo_frame: "drawer" } do %>
 
     <% if budget_category.initialized? %>
       <%# Category Header with Status Badge %>

app/views/budget_categories/_budget_category_form.html.erb

@@ -12,7 +12,7 @@
   </div>
 
   <div class="ml-auto">
-    <%= form_with model: [budget_category.budget, budget_category], data: { controller: "auto-submit-form preserve-focus" } do |f| %>
+    <%= form_with model: [budget_category.budget, budget_category], url: budget_budget_category_path(budget_category.budget, budget_category, **budget_owner_query), data: { controller: "auto-submit-form preserve-focus" } do |f| %>
       <div class="form-field w-[120px]">
         <div class="flex items-center privacy-sensitive privacy-sensitive-interactive">
           <span class="text-secondary text-sm mr-2"><%= currency.symbol %></span>

app/views/budget_categories/_confirm_button.html.erb

@@ -3,7 +3,7 @@
     text: t(".confirm"),
     variant: "primary",
     full_width: true,
-    href: budget_path(budget),
+    href: budget_path(budget, **budget_owner_query),
     method: :get,
     disabled: !budget.allocations_valid?
   ) %>

app/views/budget_categories/index.html.erb

@@ -2,8 +2,8 @@
   <%= render "budgets/budget_nav", budget: @budget %>
 <% end %>
 
-<%= content_for :previous_path, edit_budget_path(@budget) %>
-<%= content_for :cancel_path, budget_path(@budget) %>
+<%= content_for :previous_path, edit_budget_path(@budget, **budget_owner_query) %>
+<%= content_for :cancel_path, budget_path(@budget, **budget_owner_query) %>
 
 <div>
   <div class="space-y-6">

app/views/budgets/_budget_donut.html.erb

@@ -1,3 +1,5 @@
+<%# locals: (budget:, editable:) %>
+
 <%= tag.div data: { controller: "donut-chart", donut_chart_segments_value: budget.to_donut_segments_json }, class: "relative h-full" do %>
   <div data-donut-chart-target="chartContainer" class="absolute inset-0 pointer-events-none"></div>
 
@@ -12,25 +14,31 @@
           <%= format_money(budget.actual_spending_money) %>
         </div>
 
-        <%= render DS::Link.new(
-          text: t(".of_budget", amount: budget.budgeted_spending_money.format),
-          variant: "secondary",
-          icon: "pencil",
-          icon_position: "right",
-          size: "sm",
-          href: edit_budget_path(budget)
-        ) %>
+        <% if editable %>
+          <%= render DS::Link.new(
+            text: t(".of_budget", amount: budget.budgeted_spending_money.format),
+            variant: "secondary",
+            icon: "pencil",
+            icon_position: "right",
+            size: "sm",
+            href: edit_budget_path(budget, **budget_owner_query)
+          ) %>
+        <% else %>
+          <p class="text-secondary text-sm"><%= t(".of_budget", amount: budget.budgeted_spending_money.format) %></p>
+        <% end %>
       <% else %>
         <div data-donut-chart-target="amount" class="text-subdued text-3xl mb-2 privacy-sensitive whitespace-nowrap">
           <span><%= format_money Money.new(0, budget.currency || budget.family.currency) %></span>
         </div>
 
-        <%= render DS::Link.new(
-          text: t(".new_budget"),
-          size: "sm",
-          icon: "plus",
-          href: edit_budget_path(budget)
-        ) %>
+        <% if editable %>
+          <%= render DS::Link.new(
+            text: t(".new_budget"),
+            size: "sm",
+            icon: "plus",
+            href: edit_budget_path(budget, **budget_owner_query)
+          ) %>
+        <% end %>
       <% end %>
     </div>
 
@@ -46,14 +54,18 @@
             <%= format_money(bc.actual_spending_money) %>
           </p>
 
-          <%= render DS::Link.new(
-            text: t(".of_budget", amount: bc.budgeted_spending_money.format(precision: 0)),
-            variant: "secondary",
-            icon: "pencil",
-            icon_position: "right",
-            size: "sm",
-            href: budget_budget_categories_path(budget)
-          ) %>
+          <% if editable %>
+            <%= render DS::Link.new(
+              text: t(".of_budget", amount: bc.budgeted_spending_money.format(precision: 0)),
+              variant: "secondary",
+              icon: "pencil",
+              icon_position: "right",
+              size: "sm",
+              href: budget_budget_categories_path(budget, **budget_owner_query)
+            ) %>
+          <% else %>
+            <p class="text-secondary text-sm"><%= t(".of_budget", amount: bc.budgeted_spending_money.format(precision: 0)) %></p>
+          <% end %>
         </div>
       </div>
     <% end %>

app/views/budgets/_budget_header.html.erb

@@ -6,7 +6,7 @@
       <%= render DS::Link.new(
         variant: "icon",
         icon: "chevron-left",
-        href: budget_path(budget.previous_budget_param),
+        href: budget_path(budget.previous_budget_param, **budget_owner_query),
       ) %>
     <% else %>
       <span class="text-subdued">
@@ -18,7 +18,7 @@
       <%= render DS::Link.new(
         variant: "icon",
         icon: "chevron-right",
-        href: budget_path(budget.next_budget_param),
+        href: budget_path(budget.next_budget_param, **budget_owner_query),
       ) %>
     <% else %>
       <span class="text-subdued">
@@ -29,7 +29,9 @@
 
   <%= render DS::Popover.new(variant: "button") do |popover| %>
     <% popover.with_button class: "flex items-center gap-1 hover:bg-surface-hover cursor-pointer rounded-md p-2"  do %>
-      <span class="text-primary font-medium text-lg lg:text-base"><%= @budget.name %></span>
+      <span class="text-primary font-medium text-lg lg:text-base">
+        <%= @budget.name %>
+      </span>
       <%= icon("chevron-down") %>
     <% end %>
 
@@ -42,7 +44,13 @@
     <%= render DS::Link.new(
         text: t(".today"),
         variant: "outline",
-        href: budget_path(Budget.date_to_param(Date.current)),
+        href: budget_path(Budget.date_to_param(Date.current), **budget_owner_query),
     ) %>
   </div>
 </div>
+
+<% if @switch_options.present? && @switch_options.size > 1 %>
+  <div class="mb-4">
+    <%= render "budgets/owner_switcher", switch_options: @switch_options, switch_path: ->(owner_param) { budget_path(budget.to_param, owner: owner_param) } %>
+  </div>
+<% end %>

app/views/budgets/_budget_nav.html.erb

@@ -1,14 +1,14 @@
 <%# locals: (budget:) %>
 
 <% steps = [
-  { name: "Setup", path: edit_budget_path(budget), is_complete: budget.initialized?, step_number: 1 },
-  { name: "Categories", path: budget_budget_categories_path(budget), is_complete: budget.allocations_valid?, step_number: 2 },
+  { name: "Setup", path: edit_budget_path(budget, **budget_owner_query), is_complete: budget.initialized?, step_number: 1 },
+  { name: "Categories", path: budget_budget_categories_path(budget, **budget_owner_query), is_complete: budget.allocations_valid?, step_number: 2 },
 ] %>
 
 <ul class="flex items-center gap-2">
   <% steps.each_with_index do |step, idx| %>
     <li class="flex items-center gap-2 group">
-      <% is_current = request.path == step[:path] %>
+      <% is_current = request.path == step[:path].split("?").first %>
 
       <% text_class = if is_current
                   "text-primary"

app/views/budgets/_copy_previous_prompt.html.erb

@@ -11,7 +11,7 @@
   <div class="flex flex-col sm:flex-row items-center gap-2">
     <%= render DS::Button.new(
       text: t("budgets.copy_previous_prompt.copy_button", source_name: source_budget.name),
-      href: copy_previous_budget_path(budget),
+      href: copy_previous_budget_path(budget, **budget_owner_query),
       method: :post,
       icon: "copy"
     ) %>
@@ -20,7 +20,7 @@
       text: t("budgets.copy_previous_prompt.fresh_button"),
       variant: "secondary",
       icon: "plus",
-      href: edit_budget_path(budget)
+      href: edit_budget_path(budget, **budget_owner_query)
     ) %>
   </div>
 </div>

app/views/budgets/_over_allocation_warning.html.erb

@@ -1,15 +1,17 @@
-<%# locals: (budget:) %>
+<%# locals: (budget:, editable:) %>
 
 <div class="flex flex-col gap-4 items-center justify-center h-full">
   <%= icon "alert-triangle", size: "lg", color: "destructive" %>
   <p class="text-secondary text-sm text-center"><%= t(".over_allocated_message") %></p>
 
-  <%= render DS::Link.new(
-    text: t(".fix_allocations"),
-    variant: "secondary",
-    size: "sm",
-    icon: "pencil",
-    icon_position: "right",
-    href: budget_budget_categories_path(budget)
-  ) %>
+  <% if editable %>
+    <%= render DS::Link.new(
+      text: t(".fix_allocations"),
+      variant: "secondary",
+      size: "sm",
+      icon: "pencil",
+      icon_position: "right",
+      href: budget_budget_categories_path(budget, **budget_owner_query)
+    ) %>
+  <% end %>
 </div>

app/views/budgets/_owner_switcher.html.erb

@@ -0,0 +1,22 @@
+<%# locals: (switch_options:, switch_path:) %>
+
+<%# The shared .segmented-control track (bg-gray-50) is too close to both
+    the page background (bg-surface, also gray-50) and a white card
+    (bg-container) to read as its own control. Override it with
+    bg-surface-inset, the same track color DS::Tabs uses for Budgeted/Actual
+    on this same page — a utility class beats the component's own
+    `@apply bg-gray-50` in the cascade, so this doesn't touch the shared
+    CSS or affect other .segmented-control consumers (category filter). %>
+<%= render DS::SegmentedControl.new(full_width: true, aria_label: t("budgets.switcher.aria_label"), class: "bg-surface-inset") do |sc| %>
+  <% switch_options.each do |option| %>
+    <% segment_content = capture do %>
+      <% if option[:icon] %>
+        <%= icon(option[:icon], size: "xs", color: "current") %>
+      <% else %>
+        <%= render Goals::AvatarComponent.new(name: option[:label], size: "sm") %>
+      <% end %>
+      <span class="ml-1.5"><%= option[:label] %></span>
+    <% end %>
+    <% sc.with_segment segment_content, active: option[:active], href: switch_path.call(option[:owner_param]) %>
+  <% end %>
+<% end %>

app/views/budgets/_picker.html.erb

@@ -6,7 +6,7 @@
       <% last_month_of_previous_year = Date.new(year - 1, 12, 1) %>
 
       <% if Budget.budget_date_valid?(last_month_of_previous_year, family: family) %>
-        <%= link_to picker_budgets_path(year: year - 1), data: { turbo_frame: "budget_picker" }, class: "p-2 flex items-center justify-center hover:bg-surface-hover rounded-md" do %>
+        <%= link_to picker_budgets_path(year: year - 1, **budget_owner_query), data: { turbo_frame: "budget_picker" }, class: "p-2 flex items-center justify-center hover:bg-surface-hover rounded-md" do %>
           <%= icon "chevron-left" %>
         <% end %>
       <% else %>
@@ -22,7 +22,7 @@
       <% first_month_of_next_year = Date.new(year + 1, 1, 1) %>
 
       <% if Budget.budget_date_valid?(first_month_of_next_year, family: family) %>
-        <%= link_to picker_budgets_path(year: year + 1), data: { turbo_frame: "budget_picker" }, class: "p-2 flex items-center justify-center hover:bg-surface-hover rounded-md" do %>
+        <%= link_to picker_budgets_path(year: year + 1, **budget_owner_query), data: { turbo_frame: "budget_picker" }, class: "p-2 flex items-center justify-center hover:bg-surface-hover rounded-md" do %>
           <%= icon "chevron-right" %>
         <% end %>
       <% else %>
@@ -41,7 +41,7 @@
           <%= render DS::Link.new(
             variant: "ghost",
             text: month_name,
-            href: budget_path(param_key),
+            href: budget_path(param_key, **budget_owner_query),
             full_width: true,
             frame: :_top
           ) %>

app/views/budgets/edit.html.erb

@@ -2,8 +2,8 @@
   <%= render "budgets/budget_nav", budget: @budget %>
 <% end %>
 
-<%= content_for :previous_path, budget_path(@budget) %>
-<%= content_for :cancel_path, budget_path(@budget) %>
+<%= content_for :previous_path, budget_path(@budget, **budget_owner_query) %>
+<%= content_for :cancel_path, budget_path(@budget, **budget_owner_query) %>
 
 <div>
   <div class="space-y-4">
@@ -15,7 +15,7 @@
     </div>
 
     <div class="mx-auto max-w-lg">
-      <%= styled_form_with model: @budget, class: "space-y-3", data: { controller: "budget-form" } do |f| %>
+      <%= styled_form_with model: @budget, url: budget_path(@budget, **budget_owner_query), class: "space-y-3", data: { controller: "budget-form" } do |f| %>
         <%= f.money_field :budgeted_spending, label: t(".budgeted_spending"), required: true, disable_currency: true %>
         <%= f.money_field :expected_income, label: t(".expected_income"), required: true, disable_currency: true %>
 

app/views/budgets/show.html.erb

@@ -10,12 +10,12 @@
     <div class="grid grid-cols-1 md:grid-cols-2 gap-4">
       <%# Budget Donut %>
       <div class="min-h-[300px] bg-container rounded-xl shadow-border-xs p-8">
-        <% if !@budget.initialized? && @source_budget.present? %>
+        <% if !@budget.initialized? && @source_budget.present? && @editable %>
           <%= render "budgets/copy_previous_prompt", budget: @budget, source_budget: @source_budget %>
         <% elsif @budget.initialized? && @budget.available_to_allocate.negative? %>
-          <%= render "budgets/over_allocation_warning", budget: @budget %>
+          <%= render "budgets/over_allocation_warning", budget: @budget, editable: @editable %>
         <% else %>
-          <%= render "budgets/budget_donut", budget: @budget %>
+          <%= render "budgets/budget_donut", budget: @budget, editable: @editable %>
         <% end %>
       </div>
 
@@ -63,12 +63,12 @@
         <% end %>
 
         <div class="<%= has_over_budget ? "shrink-0 flex justify-end whitespace-nowrap" : "ml-auto" %>">
-          <% if @budget.initialized? %>
+          <% if @budget.initialized? && @editable %>
             <%= render DS::Link.new(
               text: t("budgets.show.categories.edit"),
               variant: "secondary",
               icon: "settings-2",
-              href: budget_budget_categories_path(@budget)
+              href: budget_budget_categories_path(@budget, **budget_owner_query)
             ) %>
           <% end %>
         </div>

app/views/plans/_budget_card.html.erb

@@ -1,4 +1,4 @@
-<%# locals: (budget:, top_budget_categories:) %>
+<%# locals: (budget:, top_budget_categories:, editable:, switch_options:) %>
 
 <%= render DS::Card.new do %>
   <div class="flex flex-wrap items-center gap-2 mb-4">
@@ -6,7 +6,9 @@
       <%= icon("layout-grid", size: "sm") %>
     </span>
     <h2 class="text-sm font-medium text-primary shrink-0"><%= t(".title") %></h2>
-    <span class="text-xs text-subdued truncate">· <%= budget.name %></span>
+    <span class="text-xs text-subdued truncate">
+      · <%= budget.name %>
+    </span>
 
     <% if budget.initialized? %>
       <% if budget.available_to_spend.negative? %>
@@ -17,24 +19,32 @@
         <%= render DS::Pill.new(label: t("reports.budget_performance.status.good"), tone: :success, marker: false, icon: "check-circle") %>
       <% end %>
 
-      <div class="ml-auto shrink-0">
-        <%# The budget donut's trailing pencil (_budget_donut.html.erb) labels
-            the VALUE itself ("$12,850 ✎" — click the number to edit it).
-            This button's label is a static action ("Edit budget"), which
-            takes a leading icon everywhere else in the app: the categories
-            "Edit" on this same page (budgets/show.html.erb) and "Edit
-            split" (transactions/show.html.erb) both do. %>
-        <%= render DS::Link.new(
-          text: t(".edit_budget"),
-          variant: "secondary",
-          size: "sm",
-          icon: "pencil",
-          href: edit_budget_path(budget)
-        ) %>
-      </div>
+      <% if editable %>
+        <div class="ml-auto shrink-0">
+          <%# The budget donut's trailing pencil (_budget_donut.html.erb) labels
+              the VALUE itself ("$12,850 ✎" — click the number to edit it).
+              This button's label is a static action ("Edit budget"), which
+              takes a leading icon everywhere else in the app: the categories
+              "Edit" on this same page (budgets/show.html.erb) and "Edit
+              split" (transactions/show.html.erb) both do. %>
+          <%= render DS::Link.new(
+            text: t(".edit_budget"),
+            variant: "secondary",
+            size: "sm",
+            icon: "pencil",
+            href: edit_budget_path(budget, **budget_owner_query)
+          ) %>
+        </div>
+      <% end %>
     <% end %>
   </div>
 
+  <% if switch_options.size > 1 %>
+    <div class="mb-4">
+      <%= render "budgets/owner_switcher", switch_options: switch_options, switch_path: ->(owner_param) { plan_path(owner: owner_param) } %>
+    </div>
+  <% end %>
+
   <% if budget.initialized? %>
     <div class="flex items-baseline gap-2">
       <span class="text-3xl font-medium text-primary tabular-nums privacy-sensitive">
@@ -90,18 +100,20 @@
         <%= icon("map", size: "md") %>
       </span>
       <p class="text-sm text-secondary max-w-xs"><%= t(".empty_body") %></p>
-      <%= render DS::Link.new(
-        text: t(".set_up"),
-        variant: "primary",
-        href: edit_budget_path(budget)
-      ) %>
+      <% if editable %>
+        <%= render DS::Link.new(
+          text: t(".set_up"),
+          variant: "primary",
+          href: edit_budget_path(budget, **budget_owner_query)
+        ) %>
+      <% end %>
     </div>
   <% end %>
 
   <%= render DS::Link.new(
     text: t(".view_budget"),
     variant: "secondary",
-    href: budget_path(budget),
+    href: budget_path(budget, **budget_owner_query),
     icon: "chevron-right",
     icon_position: :right,
     full_width: true,

app/views/plans/show.html.erb

@@ -11,7 +11,7 @@
   </header>
 
   <div class="grid grid-cols-1 @3xl:grid-cols-2 gap-4 items-stretch">
-    <%= render "plans/budget_card", budget: @budget, top_budget_categories: @top_budget_categories %>
+    <%= render "plans/budget_card", budget: @budget, top_budget_categories: @top_budget_categories, editable: @editable, switch_options: @switch_options %>
     <%= render "plans/goals_card", goals: @goals, summary: @goals_summary, linkable_account_count: @linkable_account_count, family_has_goals: @family_has_goals %>
   </div>
 </div>

app/views/settings/preferences/show.html.erb

@@ -24,6 +24,16 @@
             country_options,
             { label: t(".country") },
             { data: { auto_submit_form_target: "auto" } } %>
+        <p class="text-xs italic pl-2 text-secondary"><%= t(".translations_notice") %></p>
+      <% end %>
+    <% end %>
+  </div>
+<% end %>
+<%= settings_section title: t(".budget_title"), subtitle: t(".budget_subtitle") do %>
+  <div>
+    <%= styled_form_with model: @user, class: "space-y-4", data: { controller: "auto-submit-form" } do |form| %>
+      <%= form.hidden_field :redirect_to, value: "preferences" %>
+      <%= form.fields_for :family do |family_form| %>
         <%= family_form.select :month_start_day,
             (1..28).map { |day| [localized_ordinal(day), day] },
             { label: t(".month_start_day"), hint: t(".month_start_day_hint") },
@@ -31,11 +41,68 @@
         <% if @user.family.uses_custom_month_start? %>
           <%= render DS::Alert.new(message: t(".month_start_day_warning"), variant: :warning) %>
         <% end %>
-        <p class="text-xs italic pl-2 text-secondary"><%= t(".translations_notice") %></p>
+        <% if Current.user.admin? && preview_features_enabled? %>
+          <div class="flex items-center justify-between">
+            <div class="space-y-1">
+              <p class="text-sm flex items-center gap-1.5">
+                <%= t(".personal_budgets") %>
+                <%= render DS::Pill.new(label: t("shared.preview"), size: :sm) %>
+              </p>
+              <p class="text-secondary text-sm"><%= t(".personal_budgets_hint") %></p>
+            </div>
+            <%= family_form.toggle :personal_budgets,
+                data: { auto_submit_form_target: "auto" } %>
+          </div>
+
+          <% if @user.family.personal_budgets? %>
+            <div class="flex items-center justify-between">
+              <div class="space-y-1">
+                <p class="text-sm"><%= t(".household_budget_enabled") %></p>
+                <p class="text-secondary text-sm"><%= t(".household_budget_enabled_hint") %></p>
+              </div>
+              <%= family_form.toggle :household_budget_enabled,
+                  data: { auto_submit_form_target: "auto" } %>
+            </div>
+          <% end %>
+        <% end %>
       <% end %>
     <% end %>
   </div>
 <% end %>
+<% if @user.family.personal_budgets? && preview_features_enabled? %>
+  <%= settings_section title: t(".budget_sharing_title"), subtitle: t(".budget_sharing_subtitle") do %>
+    <% if @family_members.any? %>
+      <%= styled_form_with url: settings_budget_shares_path, method: :patch, class: "space-y-4", data: { controller: "auto-submit-form" } do |form| %>
+        <div class="bg-container-inset rounded-xl p-1">
+          <% @family_members.each_with_index do |member, index| %>
+            <% share = @budget_shares[member.id] %>
+            <% select_id = "budget_share_permission_#{member.id}" %>
+            <input type="hidden" name="budget_shares[members][<%= index %>][viewer_id]" value="<%= member.id %>">
+            <div class="flex items-center justify-between gap-3 bg-container p-4 shadow-border-xs rounded-lg mt-2">
+              <div class="flex items-center gap-2 min-w-0">
+                <div class="w-8 h-8 shrink-0 rounded-full bg-surface-inset flex items-center justify-center text-xs font-medium text-secondary">
+                  <%= member.initials %>
+                </div>
+                <span class="text-sm text-primary truncate"><%= member.display_name %></span>
+              </div>
+              <label for="<%= select_id %>" class="sr-only"><%= t(".budget_sharing_permission_label", name: member.display_name) %></label>
+              <select id="<%= select_id %>" name="budget_shares[members][<%= index %>][permission]" class="text-sm border border-primary rounded-lg px-3 py-1.5 bg-container text-primary" data-auto-submit-form-target="auto">
+                <option value="" <%= "selected" if share.nil? %>><%= t(".budget_sharing_permissions.none") %></option>
+                <% BudgetShare::PERMISSIONS.each do |perm| %>
+                  <option value="<%= perm %>" <%= "selected" if share&.permission == perm %>>
+                    <%= t(".budget_sharing_permissions.#{perm}") %>
+                  </option>
+                <% end %>
+              </select>
+            </div>
+          <% end %>
+        </div>
+      <% end %>
+    <% else %>
+      <p class="text-sm text-secondary"><%= t(".budget_sharing_no_members", moniker: family_moniker_downcase) %></p>
+    <% end %>
+  <% end %>
+<% end %>
 <% if Current.user.admin? %>
   <%= settings_section title: t(".currencies_title", moniker: family_moniker), subtitle: t(".currencies_subtitle", moniker: family_moniker_downcase) do %>
     <% selected_count_translations = t(".selected_currencies_count") %>

config/locales/views/budgets/en.yml

@@ -1,6 +1,9 @@
 ---
 en:
   budgets:
+    switcher:
+      aria_label: "Switch budget"
+      household: "Household"
     budget_donut:
       spent: "Spent"
       new_budget: "New budget"

config/locales/views/budgets/fr.yml

@@ -34,6 +34,9 @@ fr:
       status: Statut
       view_all_transactions: Voir toutes les transactions de catégorie
   budgets:
+    switcher:
+      aria_label: "Changer de budget"
+      household: "Commun"
     actuals_summary:
       expenses: Dépenses
       income: Revenu

config/locales/views/settings/en.yml

@@ -175,10 +175,24 @@ en:
         language_auto: Browser language
         page_title: Preferences
         timezone: Timezone
+        translations_notice: Please note, we are still working on translations for various languages.
+        budget_title: Budget
+        budget_subtitle: Configure how your budgets behave
         month_start_day: Budget month starts on
         month_start_day_hint: Set when your budget month starts (e.g., payday)
         month_start_day_warning: Your budgets and MTD calculations will use this custom start day instead of the 1st of each month.
-        translations_notice: Please note, we are still working on translations for various languages.
+        personal_budgets: Personal budgets
+        personal_budgets_hint: Enable individual budgets for each family member.
+        household_budget_enabled: Household budget
+        household_budget_enabled_hint: Keep a shared household budget alongside personal budgets. Turn off to use personal budgets only.
+        budget_sharing_title: Budget sharing
+        budget_sharing_subtitle: Let other members view or edit your personal budget
+        budget_sharing_no_members: No other members in your %{moniker} to share with
+        budget_sharing_permission_label: "%{name}'s access"
+        budget_sharing_permissions:
+          none: No access
+          read_only: View only
+          read_write: Can edit
         currencies_title: "%{moniker} Currencies"
         currencies_subtitle: Choose which currencies appear in money fields for your %{moniker}
         base_currency_label: Base currency
@@ -204,6 +218,9 @@ en:
         preview:
           title: Enable preview features
           description: Opt in to in-progress features tagged preview or canary.
+    budget_shares:
+      update:
+        success: Budget sharing settings updated
     profiles:
       destroy:
         cannot_remove_self: You cannot remove yourself from the account.

config/locales/views/settings/fr.yml

@@ -139,6 +139,16 @@ fr:
         additional_currencies_label: Devises supplémentaires
         base_currency_badge: Devise de base
         base_currency_label: Devise de base
+        budget_sharing_title: Partage de budget
+        budget_sharing_subtitle: Autorisez d'autres membres à consulter ou modifier votre budget personnel
+        budget_sharing_no_members: Aucun autre membre de votre %{moniker} avec qui partager
+        budget_sharing_permission_label: "Accès de %{name}"
+        budget_sharing_permissions:
+          none: Aucun accès
+          read_only: Lecture seule
+          read_write: Peut modifier
+        budget_subtitle: Configurez le fonctionnement de vos budgets
+        budget_title: Budget
         country: Pays
         currencies_more: "+%{count} de plus"
         currencies_subtitle: Choisissez les devises qui apparaissent dans les champs monétaires de votre %{moniker}
@@ -160,6 +170,10 @@ fr:
         no_additional_currencies: Aucune sélectionnée
         no_matching_currencies: Aucune devise trouvée
         page_title: Préférences
+        personal_budgets: Budgets personnels
+        personal_budgets_hint: Activer les budgets individuels pour chaque membre de la famille.
+        household_budget_enabled: Budget commun
+        household_budget_enabled_hint: Garder un budget commun au foyer en plus des budgets personnels. Désactivez pour n'utiliser que les budgets personnels.
         preview:
           description: Activez les fonctionnalités en cours étiquetées Aperçu ou Canary.
           title: Activer les fonctionnalités d'aperçu
@@ -176,6 +190,9 @@ fr:
         sharing_title: Partage de %{moniker}
         timezone: Fuseau horaire
         translations_notice: Veuillez noter que nous travaillons toujours sur des traductions dans différentes langues.
+    budget_shares:
+      update:
+        success: Paramètres de partage de budget mis à jour
     profiles:
       destroy:
         cannot_remove_self: Vous ne pouvez pas vous enlever de votre compte.

config/routes.rb

@@ -318,6 +318,7 @@ Rails.application.routes.draw do
   namespace :settings do
     resource :profile, only: [ :show, :destroy ]
     resource :preferences, only: %i[show update]
+    resource :budget_shares, only: :update
     resource :appearance, only: %i[show update]
     resource :debug, only: :show
     resource :background_jobs, controller: "background_jobs", only: :show do

db/migrate/20260818060353_add_personal_budgets.rb

@@ -0,0 +1,58 @@
+class AddPersonalBudgets < ActiveRecord::Migration[7.2]
+  def up
+    add_column :families, :personal_budgets, :boolean, default: false, null: false
+    add_column :families, :household_budget_enabled, :boolean, default: true, null: false
+
+    add_reference :budgets,
+                  :user,
+                  type: :uuid,
+                  foreign_key: { on_delete: :cascade },
+                  null: true
+
+    remove_index :budgets, name: "index_budgets_on_family_id_and_start_date_and_end_date"
+
+    add_index :budgets,
+              [ :family_id, :start_date, :end_date ],
+              unique: true,
+              where: "user_id IS NULL",
+              name: "index_budgets_shared_unique"
+
+    add_index :budgets,
+              [ :family_id, :start_date, :end_date, :user_id ],
+              unique: true,
+              where: "user_id IS NOT NULL",
+              name: "index_budgets_personal_unique"
+
+    remove_foreign_key :budget_categories, :budgets
+    add_foreign_key :budget_categories, :budgets, on_delete: :cascade
+
+    create_table :budget_shares, id: :uuid, default: -> { "gen_random_uuid()" } do |t|
+      t.references :owner, type: :uuid, null: false, foreign_key: { to_table: :users }
+      t.references :viewer, type: :uuid, null: false, foreign_key: { to_table: :users }
+      t.string :permission, null: false, default: "read_only"
+      t.timestamps
+    end
+
+    add_index :budget_shares, [ :owner_id, :viewer_id ], unique: true
+  end
+
+  def down
+    drop_table :budget_shares
+
+    remove_foreign_key :budget_categories, :budgets
+    add_foreign_key :budget_categories, :budgets
+
+    remove_index :budgets, name: "index_budgets_personal_unique"
+    remove_index :budgets, name: "index_budgets_shared_unique"
+
+    add_index :budgets,
+              [ :family_id, :start_date, :end_date ],
+              unique: true,
+              name: "index_budgets_on_family_id_and_start_date_and_end_date"
+
+    remove_reference :budgets, :user, type: :uuid, foreign_key: true
+
+    remove_column :families, :household_budget_enabled
+    remove_column :families, :personal_budgets
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.2].define(version: 2026_08_12_000000) do
+ActiveRecord::Schema[7.2].define(version: 2026_08_18_060353) do
   # These are extensions that must be enabled in order to support this database
   enable_extension "pgcrypto"
   enable_extension "plpgsql"
@@ -372,6 +372,17 @@ ActiveRecord::Schema[7.2].define(version: 2026_08_12_000000) do
     t.index ["category_id"], name: "index_budget_categories_on_category_id"
   end
 
+  create_table "budget_shares", id: :uuid, default: -> { "gen_random_uuid()" }, force: :cascade do |t|
+    t.uuid "owner_id", null: false
+    t.uuid "viewer_id", null: false
+    t.string "permission", default: "read_only", null: false
+    t.datetime "created_at", null: false
+    t.datetime "updated_at", null: false
+    t.index ["owner_id", "viewer_id"], name: "index_budget_shares_on_owner_id_and_viewer_id", unique: true
+    t.index ["owner_id"], name: "index_budget_shares_on_owner_id"
+    t.index ["viewer_id"], name: "index_budget_shares_on_viewer_id"
+  end
+
   create_table "budgets", id: :uuid, default: -> { "gen_random_uuid()" }, force: :cascade do |t|
     t.uuid "family_id", null: false
     t.date "start_date", null: false
@@ -381,8 +392,11 @@ ActiveRecord::Schema[7.2].define(version: 2026_08_12_000000) do
     t.string "currency", null: false
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
-    t.index ["family_id", "start_date", "end_date"], name: "index_budgets_on_family_id_and_start_date_and_end_date", unique: true
+    t.uuid "user_id"
+    t.index ["family_id", "start_date", "end_date", "user_id"], name: "index_budgets_personal_unique", unique: true, where: "(user_id IS NOT NULL)"
+    t.index ["family_id", "start_date", "end_date"], name: "index_budgets_shared_unique", unique: true, where: "(user_id IS NULL)"
     t.index ["family_id"], name: "index_budgets_on_family_id"
+    t.index ["user_id"], name: "index_budgets_on_user_id"
   end
 
   create_table "categories", id: :uuid, default: -> { "gen_random_uuid()" }, force: :cascade do |t|
@@ -775,6 +789,8 @@ ActiveRecord::Schema[7.2].define(version: 2026_08_12_000000) do
     t.string "default_account_sharing", default: "shared", null: false
     t.string "enabled_currencies", array: true
     t.datetime "last_sync_all_attempted_at"
+    t.boolean "personal_budgets", default: false, null: false
+    t.boolean "household_budget_enabled", default: true, null: false
     t.check_constraint "default_account_sharing::text = ANY (ARRAY['shared'::character varying, 'private'::character varying]::text[])", name: "chk_families_default_account_sharing"
     t.check_constraint "month_start_day >= 1 AND month_start_day <= 28", name: "month_start_day_range"
   end
@@ -2342,9 +2358,12 @@ ActiveRecord::Schema[7.2].define(version: 2026_08_12_000000) do
   add_foreign_key "binance_items", "families"
   add_foreign_key "brex_accounts", "brex_items"
   add_foreign_key "brex_items", "families"
-  add_foreign_key "budget_categories", "budgets"
+  add_foreign_key "budget_categories", "budgets", on_delete: :cascade
   add_foreign_key "budget_categories", "categories"
+  add_foreign_key "budget_shares", "users", column: "owner_id"
+  add_foreign_key "budget_shares", "users", column: "viewer_id"
   add_foreign_key "budgets", "families"
+  add_foreign_key "budgets", "users", on_delete: :cascade
   add_foreign_key "categories", "families"
   add_foreign_key "chats", "users"
   add_foreign_key "coinbase_accounts", "coinbase_items"

test/controllers/api/v1/budget_categories_controller_test.rb

@@ -129,6 +129,31 @@ class Api::V1::BudgetCategoriesControllerTest < ActionDispatch::IntegrationTest
     assert_equal "validation_failed", response_data["error"]
   end
 
+  test "excludes another family member's personal budget category" do
+    @family.update!(personal_budgets: true)
+
+    other_member_budget = @family.budgets.create!(
+      user: users(:family_member),
+      start_date: 7.months.ago.beginning_of_month.to_date,
+      end_date: 7.months.ago.end_of_month.to_date,
+      budgeted_spending: 800,
+      currency: "USD"
+    )
+    other_member_budget_category = other_member_budget.budget_categories.create!(
+      category: @category,
+      budgeted_spending: 200,
+      currency: "USD"
+    )
+
+    get api_v1_budget_categories_url, headers: api_headers(@api_key)
+    assert_response :success
+    response_data = JSON.parse(response.body)
+    assert_not_includes response_data["budget_categories"].map { |budget_category| budget_category["id"] }, other_member_budget_category.id
+
+    get api_v1_budget_category_url(other_member_budget_category), headers: api_headers(@api_key)
+    assert_response :not_found
+  end
+
   test "requires authentication" do
     get api_v1_budget_categories_url
 

test/controllers/api/v1/budgets_controller_test.rb

@@ -116,6 +116,47 @@ class Api::V1::BudgetsControllerTest < ActionDispatch::IntegrationTest
     assert_equal "validation_failed", response_data["error"]
   end
 
+  test "excludes another family member's personal budget" do
+    @family.update!(personal_budgets: true)
+
+    other_member_budget = @family.budgets.create!(
+      user: users(:family_member),
+      start_date: 5.months.ago.beginning_of_month.to_date,
+      end_date: 5.months.ago.end_of_month.to_date,
+      budgeted_spending: 800,
+      currency: "USD"
+    )
+
+    get api_v1_budgets_url, headers: api_headers(@api_key)
+    assert_response :success
+    response_data = JSON.parse(response.body)
+    assert_not_includes response_data["budgets"].map { |budget| budget["id"] }, other_member_budget.id
+
+    get api_v1_budget_url(other_member_budget.id), headers: api_headers(@api_key)
+    assert_response :not_found
+  end
+
+  test "includes another family member's personal budget once they share it" do
+    @family.update!(personal_budgets: true)
+
+    other_member_budget = @family.budgets.create!(
+      user: users(:family_member),
+      start_date: 5.months.ago.beginning_of_month.to_date,
+      end_date: 5.months.ago.end_of_month.to_date,
+      budgeted_spending: 800,
+      currency: "USD"
+    )
+    BudgetShare.create!(owner: users(:family_member), viewer: @user, permission: "read_only")
+
+    get api_v1_budgets_url, headers: api_headers(@api_key)
+    assert_response :success
+    response_data = JSON.parse(response.body)
+    assert_includes response_data["budgets"].map { |budget| budget["id"] }, other_member_budget.id
+
+    get api_v1_budget_url(other_member_budget.id), headers: api_headers(@api_key)
+    assert_response :success
+  end
+
   test "requires authentication" do
     get api_v1_budgets_url
 

test/controllers/budget_categories_controller_test.rb

@@ -139,6 +139,24 @@ class BudgetCategoriesControllerTest < ActionDispatch::IntegrationTest
       "matched funds_movement inflow must not appear in Uncategorized drilldown"
   end
 
+  test "show and update do not leak another member's personal budget category" do
+    @family.update!(personal_budgets: true)
+
+    other_member_budget = Budget.find_or_bootstrap(@family, start_date: @budget.start_date, user: users(:family_member))
+    other_budget_category = other_member_budget.budget_categories.find_by!(category: @parent_category)
+    other_budget_category.update!(budgeted_spending: 999)
+
+    get budget_budget_category_path(@budget, other_budget_category)
+    assert_response :not_found
+
+    patch budget_budget_category_path(@budget, other_budget_category),
+          params: { budget_category: { budgeted_spending: 1 } },
+          as: :turbo_stream
+    assert_response :not_found
+
+    assert_equal 999.0, other_budget_category.reload.budgeted_spending.to_f
+  end
+
   test "show drilldown still lists loan_payment transfers (intentionally budget-tracked)" do
     # loan_payment is NOT in BUDGET_EXCLUDED_KINDS. The drilldown should
     # keep showing loan_payment transfers so the user can see what's
@@ -163,3 +181,37 @@ class BudgetCategoriesControllerTest < ActionDispatch::IntegrationTest
       "loan_payment outflow remains visible (kind is not BUDGET_EXCLUDED)"
   end
 end
+
+class BudgetCategoriesControllerSharingTest < ActionDispatch::IntegrationTest
+  setup do
+    @family = families(:empty)
+    @family.update!(personal_budgets: true)
+    @owner = users(:josh)
+    @viewer = users(:ann)
+    @date = Date.current.beginning_of_month
+    @family.categories.create!(name: "Groceries", color: "#6172F3")
+    @owner_budget = Budget.find_or_bootstrap(@family, start_date: @date, user: @owner)
+  end
+
+  test "a read_only viewer cannot reach the categories wizard for the owner's budget" do
+    BudgetShare.create!(owner: @owner, viewer: @viewer, permission: "read_only")
+    sign_in @viewer
+
+    get budget_budget_categories_path(@owner_budget, owner: @owner.id)
+
+    assert_response :not_found
+  end
+
+  test "a read_write viewer can update a category on the owner's budget" do
+    BudgetShare.create!(owner: @owner, viewer: @viewer, permission: "read_write")
+    budget_category = @owner_budget.budget_categories.first
+    sign_in @viewer
+
+    patch budget_budget_category_path(@owner_budget, budget_category, owner: @owner.id),
+          params: { budget_category: { budgeted_spending: 250 } },
+          as: :turbo_stream
+
+    assert_response :success
+    assert_equal 250.0, budget_category.reload.budgeted_spending.to_f
+  end
+end

test/controllers/budgets_controller_test.rb

@@ -36,3 +36,74 @@ class BudgetsControllerTest < ActionDispatch::IntegrationTest
     assert_select "a[href=?]", budgets_path, minimum: 1
   end
 end
+
+class BudgetsControllerSharingTest < ActionDispatch::IntegrationTest
+  setup do
+    @family = families(:empty)
+    @family.update!(personal_budgets: true)
+    @owner = users(:josh)
+    @viewer = users(:ann)
+    @date = Date.current.beginning_of_month
+  end
+
+  test "household budget is viewable and editable by any family member" do
+    Budget.find_or_bootstrap(@family, start_date: @date, user: @owner, household: true)
+    sign_in @viewer
+
+    get budget_url(Budget.date_to_param(@date), params: { owner: "household" })
+    assert_response :success
+
+    patch budget_url(Budget.date_to_param(@date), params: { owner: "household" }),
+          params: { budget: { budgeted_spending: 1000, expected_income: 2000 } }
+    assert_response :redirect
+  end
+
+  test "household tab is unreachable once household_budget_enabled is off, falling back to the viewer's own budget" do
+    @family.update!(household_budget_enabled: false)
+    sign_in @viewer
+
+    get budget_url(Budget.date_to_param(@date), params: { owner: "household" })
+
+    assert_response :success
+    assert_equal @viewer.id, Budget.find_by(family: @family, start_date: @date).user_id
+  end
+
+  test "a member without a BudgetShare cannot view another member's personal budget" do
+    Budget.find_or_bootstrap(@family, start_date: @date, user: @owner)
+    sign_in @viewer
+
+    get budget_url(Budget.date_to_param(@date), params: { owner: @owner.id })
+
+    # Falls back to the viewer's own budget rather than the owner's.
+    assert_response :success
+    assert Budget.exists?(family: @family, start_date: @date, user_id: @viewer.id)
+  end
+
+  test "a read_only BudgetShare lets the viewer see but not edit the owner's budget" do
+    Budget.find_or_bootstrap(@family, start_date: @date, user: @owner)
+    BudgetShare.create!(owner: @owner, viewer: @viewer, permission: "read_only")
+    sign_in @viewer
+
+    get budget_url(Budget.date_to_param(@date), params: { owner: @owner.id })
+    assert_response :success
+
+    get edit_budget_url(Budget.date_to_param(@date), params: { owner: @owner.id })
+    assert_response :not_found
+
+    patch budget_url(Budget.date_to_param(@date), params: { owner: @owner.id }),
+          params: { budget: { budgeted_spending: 1000, expected_income: 2000 } }
+    assert_response :not_found
+  end
+
+  test "a read_write BudgetShare lets the viewer edit the owner's budget" do
+    Budget.find_or_bootstrap(@family, start_date: @date, user: @owner)
+    BudgetShare.create!(owner: @owner, viewer: @viewer, permission: "read_write")
+    sign_in @viewer
+
+    patch budget_url(Budget.date_to_param(@date), params: { owner: @owner.id }),
+          params: { budget: { budgeted_spending: 1000, expected_income: 2000 } }
+
+    assert_redirected_to budget_budget_categories_url(Budget.date_to_param(@date), owner: @owner.id)
+    assert_equal 1000, Budget.find_by(family: @family, user: @owner).budgeted_spending.to_i
+  end
+end

test/controllers/plans_controller_test.rb

@@ -65,3 +65,34 @@ class PlansControllerTest < ActionDispatch::IntegrationTest
     assert_select "a[href=?]", edit_budget_path(Budget.date_to_param(Date.current))
   end
 end
+
+class PlansControllerHouseholdSwitchingTest < ActionDispatch::IntegrationTest
+  setup do
+    @family = families(:empty)
+    @family.update!(personal_budgets: true)
+    @owner = users(:josh)
+    @owner.update!(preferences: (@owner.preferences || {}).merge("preview_features_enabled" => true))
+    sign_in @owner
+    ensure_tailwind_build
+  end
+
+  test "renders a household/mine switcher once personal_budgets is on, and switches to household" do
+    get plan_url
+
+    assert_response :success
+    assert_select "a[href=?]", plan_path(owner: "household")
+    assert_select "a[href=?]", plan_path(owner: @owner.id)
+
+    get plan_url, params: { owner: "household" }
+    assert_response :success
+  end
+
+  test "hides the household pill when household_budget_enabled is off" do
+    @family.update!(household_budget_enabled: false)
+
+    get plan_url
+
+    assert_response :success
+    assert_select "a[href=?]", plan_path(owner: "household"), count: 0
+  end
+end

test/controllers/settings/budget_shares_controller_test.rb

@@ -0,0 +1,50 @@
+require "test_helper"
+
+class Settings::BudgetSharesControllerTest < ActionDispatch::IntegrationTest
+  setup do
+    @family = families(:empty)
+    @owner = users(:josh)
+    @viewer = users(:ann)
+    sign_in @owner
+  end
+
+  test "grants a new share with the selected permission" do
+    patch settings_budget_shares_url, params: {
+      budget_shares: { members: { "0" => { viewer_id: @viewer.id, permission: "read_only" } } }
+    }
+
+    assert_redirected_to settings_preferences_path
+    share = @owner.budget_shares_given.find_by(viewer: @viewer)
+    assert_equal "read_only", share.permission
+  end
+
+  test "updates an existing share's permission" do
+    BudgetShare.create!(owner: @owner, viewer: @viewer, permission: "read_only")
+
+    patch settings_budget_shares_url, params: {
+      budget_shares: { members: { "0" => { viewer_id: @viewer.id, permission: "read_write" } } }
+    }
+
+    assert_equal "read_write", @owner.budget_shares_given.find_by(viewer: @viewer).permission
+  end
+
+  test "revokes a share when permission is blank" do
+    BudgetShare.create!(owner: @owner, viewer: @viewer, permission: "read_only")
+
+    patch settings_budget_shares_url, params: {
+      budget_shares: { members: { "0" => { viewer_id: @viewer.id, permission: "" } } }
+    }
+
+    assert_nil @owner.budget_shares_given.find_by(viewer: @viewer)
+  end
+
+  test "ignores a viewer_id outside the current user's family" do
+    outsider = users(:family_admin)
+
+    patch settings_budget_shares_url, params: {
+      budget_shares: { members: { "0" => { viewer_id: outsider.id, permission: "read_only" } } }
+    }
+
+    assert_nil BudgetShare.find_by(owner: @owner, viewer: outsider)
+  end
+end

test/controllers/settings/preferences_controller_test.rb

@@ -50,4 +50,33 @@ class Settings::PreferencesControllerTest < ActionDispatch::IntegrationTest
     assert_redirected_to settings_preferences_url
     assert_not user.reload.preview_features_enabled?
   end
+
+  test "household budget toggle and sharing card only render once personal_budgets is on" do
+    user = users(:family_admin)
+    user.update!(preferences: (user.preferences || {}).merge("preview_features_enabled" => true))
+
+    get settings_preferences_url
+    assert_response :success
+    assert_not_includes response.body, I18n.t("settings.preferences.show.household_budget_enabled")
+    assert_not_includes response.body, I18n.t("settings.preferences.show.budget_sharing_title")
+
+    user.family.update!(personal_budgets: true)
+
+    get settings_preferences_url
+    assert_response :success
+    assert_includes response.body, I18n.t("settings.preferences.show.household_budget_enabled")
+    assert_includes response.body, I18n.t("settings.preferences.show.budget_sharing_title")
+  end
+
+  test "hides the sharing card when personal_budgets is on but preview features are off" do
+    user = users(:family_admin)
+    user.family.update!(personal_budgets: true)
+    assert_not user.preview_features_enabled?
+
+    get settings_preferences_url
+
+    assert_response :success
+    assert_not_includes response.body, I18n.t("settings.preferences.show.household_budget_enabled")
+    assert_not_includes response.body, I18n.t("settings.preferences.show.budget_sharing_title")
+  end
 end

test/fixtures/users.yml

@@ -104,3 +104,29 @@ sso_only:
   role: admin
   onboarded_at: <%= 1.day.ago %>
   ai_enabled: true
+
+# Additional test users expected by PersonalBudgetTest
+josh:
+  family: empty
+  first_name: Josh
+  last_name: Tester
+  email: josh@example.com
+  password_digest: $2a$12$XoNBo/cMCyzpYtvhrPAhsubG21mELX48RAcjSVCRctW8dG8wrDIla
+  onboarded_at: <%= 2.days.ago %>
+  role: member
+  ai_enabled: true
+  show_sidebar: true
+  show_ai_sidebar: true
+
+ann:
+  family: empty
+  first_name: Ann
+  last_name: Tester
+  email: ann@example.com
+  password_digest: $2a$12$XoNBo/cMCyzpYtvhrPAhsubG21mELX48RAcjSVCRctW8dG8wrDIla
+  onboarded_at: <%= 2.days.ago %>
+  role: member
+  ai_enabled: true
+  show_sidebar: true
+  show_ai_sidebar: true
+

test/models/assistant/function/get_budget_test.rb

@@ -102,6 +102,20 @@ class Assistant::Function::GetBudgetTest < ActiveSupport::TestCase
     assert_equal target, month[:period][:start_date]
   end
 
+  test "does not leak another family member's personal budget in trend months" do
+    @family.update!(personal_budgets: true)
+    prior_start = Date.current.beginning_of_month << 1
+
+    other_budget = Budget.find_or_bootstrap(@family, start_date: prior_start, user: users(:family_member))
+    other_bc = other_budget.budget_categories.find { |bc| bc.category == categories(:food_and_drink) }
+    other_bc.update!(budgeted_spending: 12345)
+
+    result = @function.call("prior_months" => 1)
+
+    assert_equal 1, result[:months].length, "another member's personal budget must not surface as a trend month"
+    assert_equal 1, result[:months_unavailable]
+  end
+
   test "raises on invalid month format" do
     assert_raises(Assistant::Error) do
       @function.call("month" => "not-a-month")

test/models/budget_share_test.rb

@@ -0,0 +1,47 @@
+require "test_helper"
+
+class BudgetShareTest < ActiveSupport::TestCase
+  setup do
+    @owner = users(:josh)
+    @viewer = users(:ann)
+  end
+
+  test "valid with a family member and a permitted permission" do
+    share = BudgetShare.new(owner: @owner, viewer: @viewer, permission: "read_only")
+
+    assert share.valid?
+  end
+
+  test "invalid with a permission outside PERMISSIONS" do
+    share = BudgetShare.new(owner: @owner, viewer: @viewer, permission: "full_control")
+
+    assert_not share.valid?
+  end
+
+  test "invalid sharing with yourself" do
+    share = BudgetShare.new(owner: @owner, viewer: @owner, permission: "read_only")
+
+    assert_not share.valid?
+  end
+
+  test "invalid across families" do
+    outsider = users(:family_admin)
+    share = BudgetShare.new(owner: @owner, viewer: outsider, permission: "read_only")
+
+    assert_not share.valid?
+  end
+
+  test "invalid with a duplicate owner/viewer pair" do
+    BudgetShare.create!(owner: @owner, viewer: @viewer, permission: "read_only")
+    duplicate = BudgetShare.new(owner: @owner, viewer: @viewer, permission: "read_write")
+
+    assert_not duplicate.valid?
+  end
+
+  test "read_write? and read_only? reflect the permission" do
+    share = BudgetShare.new(owner: @owner, viewer: @viewer, permission: "read_write")
+
+    assert share.read_write?
+    assert_not share.read_only?
+  end
+end

test/models/personal_budget_test.rb

@@ -0,0 +1,183 @@
+require "test_helper"
+
+class PersonalBudgetTest < ActiveSupport::TestCase
+  include EntriesTestHelper
+
+  setup do
+    @family = families(:empty)
+    @user1 = users(:josh)
+    @user2 = users(:ann)
+    @date = Date.current.beginning_of_month
+  end
+
+  test "shared budget by default" do
+    @family.update!(personal_budgets: false)
+
+    budget1 = Budget.find_or_bootstrap(@family, start_date: @date, user: @user1)
+    budget2 = Budget.find_or_bootstrap(@family, start_date: @date, user: @user2)
+
+    assert_equal budget1.id, budget2.id
+    assert_nil budget1.user_id
+  end
+
+  test "separate budgets when personal_budgets is enabled" do
+    @family.update!(personal_budgets: true)
+
+    budget1 = Budget.find_or_bootstrap(@family, start_date: @date, user: @user1)
+    budget2 = Budget.find_or_bootstrap(@family, start_date: @date, user: @user2)
+
+    assert_not_equal budget1.id, budget2.id
+    assert_equal @user1.id, budget1.user_id
+    assert_equal @user2.id, budget2.user_id
+  end
+
+  test "find_or_bootstrap handles transition from shared to personal" do
+    @family.update!(personal_budgets: false)
+    shared_budget = Budget.find_or_bootstrap(@family, start_date: @date, user: @user1)
+
+    @family.update!(personal_budgets: true)
+    personal_budget = Budget.find_or_bootstrap(@family, start_date: @date, user: @user1)
+
+    assert_not_equal shared_budget.id, personal_budget.id
+    assert_equal @user1.id, personal_budget.user_id
+  end
+
+  test "most_recent_initialized_budget does not bleed across users" do
+    @family.update!(personal_budgets: true)
+
+    past_date = 1.month.ago.beginning_of_month
+
+    # user1 has an initialized budget last month
+    user1_past = Budget.find_or_bootstrap(@family, start_date: past_date, user: @user1)
+    user1_past.update!(budgeted_spending: 3000, expected_income: 5000)
+
+    # user2 has no budget last month — creates a fresh one for this month
+    user2_current = Budget.find_or_bootstrap(@family, start_date: @date, user: @user2)
+
+    # user2's source should be nil, not user1's past budget
+    assert_nil user2_current.most_recent_initialized_budget
+  end
+
+  test "copy_previous does not copy another users budget" do
+    @family.update!(personal_budgets: true)
+
+    past_date = 1.month.ago.beginning_of_month
+
+    user1_past = Budget.find_or_bootstrap(@family, start_date: past_date, user: @user1)
+    user1_past.update!(budgeted_spending: 9999, expected_income: 9999)
+
+    user2_current = Budget.find_or_bootstrap(@family, start_date: @date, user: @user2)
+
+    # copy_from! should not find user1's budget as source
+    source = user2_current.most_recent_initialized_budget
+    assert_nil source
+    assert_nil user2_current.budgeted_spending
+  end
+
+  test "copy_from! rejects a source budget owned by another user" do
+    @family.update!(personal_budgets: true)
+
+    past_date = 1.month.ago.beginning_of_month
+
+    user1_past = Budget.find_or_bootstrap(@family, start_date: past_date, user: @user1)
+    user1_past.update!(budgeted_spending: 9999, expected_income: 9999)
+
+    user2_current = Budget.find_or_bootstrap(@family, start_date: @date, user: @user2)
+
+    assert_raises(ArgumentError) { user2_current.copy_from!(user1_past) }
+  end
+
+  test "deleting a user cascades through their personal budget and budget categories" do
+    @family.update!(personal_budgets: true)
+    category = @family.categories.create!(name: "Groceries", color: "#6172F3")
+
+    budget = Budget.find_or_bootstrap(@family, start_date: @date, user: @user1)
+    budget.update!(budgeted_spending: 500, expected_income: 1000)
+    budget_category = budget.budget_categories.find_by!(category_id: category.id)
+
+    assert_nothing_raised { @user1.destroy! }
+
+    assert_nil Budget.find_by(id: budget.id)
+    assert_nil BudgetCategory.find_by(id: budget_category.id)
+  end
+
+  test "household and personal budgets coexist when household: true is explicitly requested" do
+    @family.update!(personal_budgets: true)
+
+    household_budget = Budget.find_or_bootstrap(@family, start_date: @date, user: @user1, household: true)
+    personal_budget = Budget.find_or_bootstrap(@family, start_date: @date, user: @user1)
+
+    assert_not_equal household_budget.id, personal_budget.id
+    assert_nil household_budget.user_id
+    assert_equal @user1.id, personal_budget.user_id
+  end
+
+  test "household: true returns nil when the family disabled household_budget_enabled" do
+    @family.update!(personal_budgets: true, household_budget_enabled: false)
+
+    assert_nil Budget.find_or_bootstrap(@family, start_date: @date, user: @user1, household: true)
+  end
+
+  test "household: true ignores household_budget_enabled when personal_budgets is off" do
+    @family.update!(personal_budgets: false, household_budget_enabled: false)
+
+    budget = Budget.find_or_bootstrap(@family, start_date: @date, user: @user1, household: true)
+
+    assert budget.present?
+    assert_nil budget.user_id
+  end
+
+  test "viewable_by? and editable_by? allow every family member on the household budget" do
+    household_budget = Budget.find_or_bootstrap(@family, start_date: @date, user: @user1, household: true)
+
+    assert household_budget.viewable_by?(@user1)
+    assert household_budget.viewable_by?(@user2)
+    assert household_budget.editable_by?(@user1)
+    assert household_budget.editable_by?(@user2)
+  end
+
+  test "viewable_by? and editable_by? restrict a personal budget to its owner by default" do
+    @family.update!(personal_budgets: true)
+    personal_budget = Budget.find_or_bootstrap(@family, start_date: @date, user: @user1)
+
+    assert personal_budget.viewable_by?(@user1)
+    assert personal_budget.editable_by?(@user1)
+    assert_not personal_budget.viewable_by?(@user2)
+    assert_not personal_budget.editable_by?(@user2)
+  end
+
+  test "a read_only BudgetShare grants viewing but not editing" do
+    @family.update!(personal_budgets: true)
+    personal_budget = Budget.find_or_bootstrap(@family, start_date: @date, user: @user1)
+    BudgetShare.create!(owner: @user1, viewer: @user2, permission: "read_only")
+
+    assert personal_budget.viewable_by?(@user2)
+    assert_not personal_budget.editable_by?(@user2)
+  end
+
+  test "a read_write BudgetShare grants both viewing and editing" do
+    @family.update!(personal_budgets: true)
+    personal_budget = Budget.find_or_bootstrap(@family, start_date: @date, user: @user1)
+    BudgetShare.create!(owner: @user1, viewer: @user2, permission: "read_write")
+
+    assert personal_budget.viewable_by?(@user2)
+    assert personal_budget.editable_by?(@user2)
+  end
+
+  test "household actual spending reflects the viewer's accessible accounts, personal reflects only the owner's own" do
+    @family.update!(personal_budgets: true)
+
+    owned_account = Account.create!(family: @family, accountable: Depository.new, name: "Josh checking", status: "active", currency: "USD", balance: 0, owner: @user1)
+    joint_account = Account.create!(family: @family, accountable: Depository.new, name: "Joint savings", status: "active", currency: "USD", balance: 0, owner: @user2)
+    AccountShare.create!(account: joint_account, user: @user1, permission: "read_write", include_in_finances: true)
+
+    create_transaction(account: owned_account, amount: 50, date: @date)
+    create_transaction(account: joint_account, amount: 200, date: @date)
+
+    household_budget = Budget.find_or_bootstrap(@family, start_date: @date, user: @user1, household: true)
+    personal_budget = Budget.find_or_bootstrap(@family, start_date: @date, user: @user1)
+
+    assert_equal 250.0, household_budget.actual_spending.to_f
+    assert_equal 50.0, personal_budget.actual_spending.to_f
+  end
+end

test/views/budgets/budget_donut_view_test.rb

@@ -46,7 +46,7 @@ class BudgetDonutViewTest < ActionView::TestCase
     budget = Budget.find(budget.id)
     uncategorized = budget.uncategorized_budget_category
 
-    html = render(partial: "budgets/budget_donut", locals: { budget: budget })
+    html = render(partial: "budgets/budget_donut", locals: { budget: budget, editable: true })
 
     assert_includes html, "segment_#{uncategorized.id}"
     assert_includes html, uncategorized.category.display_name