diff --git a/app/models/ibkr_account/historical_balances_sync.rb b/app/models/ibkr_account/historical_balances_sync.rb
index 4d302d7ba..45155a26e 100644
--- a/app/models/ibkr_account/historical_balances_sync.rb
+++ b/app/models/ibkr_account/historical_balances_sync.rb
@@ -11,8 +11,11 @@ class IbkrAccount::HistoricalBalancesSync
     return unless account.present?
     return if normalized_rows.empty?
 
+    rows = balance_rows
+    return if rows.empty?
+
     account.balances.upsert_all(
-      balance_rows,
+      rows,
       unique_by: %i[account_id date currency]
     )
   end
@@ -109,12 +112,35 @@ class IbkrAccount::HistoricalBalancesSync
 
     def balance_rows
       current_time = Time.current
+      trade_flows_by_date  # ensure @failed_fx_dates is populated before iterating
 
-      normalized_rows.each_with_index.map do |row, index|
+      normalized_rows.each_with_index.filter_map do |row, index|
+        next if @failed_fx_dates.include?(row[:date])
         previous_row = index.zero? ? nil : normalized_rows[index - 1]
         start_cash_balance     = previous_row ? previous_row[:cash]     : row[:cash]
         start_non_cash_balance = previous_row ? previous_row[:non_cash] : row[:non_cash]
 
+        # Derive market return directly from IBKR's equity data so Period Return
+        # matches IBKR without requiring third-party security price providers.
+        #
+        # nmf = Δnon_cash - net_buy_sell
+        #   Δnon_cash  : change in holdings value per IBKR equity summary (exact)
+        #   net_buy_sell: sum of trade entry amounts converted to base currency
+        #                 (positive = buy, negative = sell; IBKR fx_rate_to_base applied)
+        #
+        # non_cash_adjustments absorbs net_buy_sell so the virtual column
+        # end_non_cash_balance = start + nmf + adjustments stays equal to row[:non_cash].
+        if previous_row
+          net_buy_sell = trade_flows_by_date[row[:date]] || 0
+          nmf          = row[:non_cash] - start_non_cash_balance - net_buy_sell
+          non_cash_adj = net_buy_sell
+        else
+          # First-day row has no prior period to diff against, so both values are
+          # intentionally zero — not a bug, just an unavoidable bootstrap constraint.
+          nmf          = 0
+          non_cash_adj = 0
+        end
+
         {
           account_id: account.id,
           date: row[:date],
@@ -127,13 +153,44 @@ class IbkrAccount::HistoricalBalancesSync
           cash_outflows: 0,
           non_cash_inflows: 0,
           non_cash_outflows: 0,
-          net_market_flows: 0,
+          net_market_flows: nmf,
           cash_adjustments: row[:cash] - start_cash_balance,
-          non_cash_adjustments: row[:non_cash] - start_non_cash_balance,
+          non_cash_adjustments: non_cash_adj,
           flows_factor: 1,
           created_at: current_time,
           updated_at: current_time
         }
       end
     end
+
+    # Net value of all trades on each date, in account base currency.
+    # Uses the IBKR-provided fx_rate_to_base stored on each Trade entry so the
+    # conversion is exact and consistent with IBKR's own calculations.
+    # Positive = net buy (cash out), negative = net sell (cash in).
+    def trade_flows_by_date
+      @trade_flows_by_date ||= begin
+        @failed_fx_dates = []
+        if account
+          account.entries
+            .joins("INNER JOIN trades ON trades.id = entries.entryable_id AND entries.entryable_type = 'Trade'")
+            .where.not(trades: { qty: 0 })
+            .includes(:entryable)
+            .each_with_object(Hash.new(0)) do |entry, flows|
+              custom_rate = entry.entryable.exchange_rate
+              base_amount = Money.new(entry.amount, entry.currency)
+                .exchange_to(account_currency, custom_rate: custom_rate, date: entry.date)
+                .amount
+              flows[entry.date] += base_amount
+            rescue Money::ConversionError
+              Rails.logger.warn(
+                "IbkrAccount::HistoricalBalancesSync - No FX rate for #{entry.currency}→#{account_currency} " \
+                "on #{entry.date}; balance row for this date will not be persisted"
+              )
+              @failed_fx_dates << entry.date
+            end
+        else
+          {}
+        end
+      end
+    end
 end
diff --git a/test/models/ibkr_account/historical_balances_sync_test.rb b/test/models/ibkr_account/historical_balances_sync_test.rb
index 66b5ee89b..825cc1aaf 100644
--- a/test/models/ibkr_account/historical_balances_sync_test.rb
+++ b/test/models/ibkr_account/historical_balances_sync_test.rb
@@ -213,6 +213,163 @@ class IbkrAccount::HistoricalBalancesSyncTest < ActiveSupport::TestCase
     assert_not_nil @account.balances.find_by(date: Date.new(2026, 5, 8), currency: "CHF")
   end
 
+  test "computes net_market_flows from equity delta minus trade flows" do
+    # Day 1: total=3000, cash=500, non_cash=2500
+    # Day 2: total=3200, cash=500, non_cash=2700  (Δnon_cash=200)
+    #   Buy trade on Day 2: CHF 150 (same currency as account, no FX)
+    #   nmf = 200 - 150 = 50
+    @ibkr_account.update!(
+      raw_equity_summary_payload: [
+        { report_date: "2026-05-07", total: "3000.00" },
+        { report_date: "2026-05-08", total: "3200.00" }
+      ]
+    )
+    seed_balance(date: Date.new(2026, 5, 7), balance: 3000.00, cash_balance: 500.00)
+    seed_balance(date: Date.new(2026, 5, 8), balance: 3200.00, cash_balance: 500.00)
+
+    security = Security.create!(ticker: "TEST", name: "Test Stock")
+    @account.entries.create!(
+      name: "Buy 100 TEST",
+      date: Date.new(2026, 5, 8),
+      amount: 150.00,
+      currency: "CHF",
+      entryable: Trade.new(security: security, qty: 100, price: 1.5, currency: "CHF")
+    )
+
+    IbkrAccount::HistoricalBalancesSync.new(@ibkr_account).sync!
+
+    day1 = @account.balances.find_by!(date: Date.new(2026, 5, 7), currency: "CHF")
+    day2 = @account.balances.find_by!(date: Date.new(2026, 5, 8), currency: "CHF")
+
+    assert_equal BigDecimal("0"),   day1.net_market_flows
+    assert_equal BigDecimal("50"),  day2.net_market_flows
+
+    # Virtual column must still resolve to IBKR's equity total minus cash
+    assert_equal BigDecimal("2500.00"), day1.end_non_cash_balance
+    assert_equal BigDecimal("2700.00"), day2.end_non_cash_balance
+  end
+
+  test "applies fx_rate_to_base when trade currency differs from account currency" do
+    # Trade in EUR with fx_rate_to_base=1.1 → CHF 165, not CHF 150
+    # Day 1: non_cash=2500, Day 2: non_cash=2700 (Δ=200)
+    # nmf = 200 - 165 = 35
+    @ibkr_account.update!(
+      raw_equity_summary_payload: [
+        { report_date: "2026-05-07", total: "3000.00" },
+        { report_date: "2026-05-08", total: "3200.00" }
+      ]
+    )
+    seed_balance(date: Date.new(2026, 5, 7), balance: 3000.00, cash_balance: 500.00)
+    seed_balance(date: Date.new(2026, 5, 8), balance: 3200.00, cash_balance: 500.00)
+
+    security = Security.create!(ticker: "TEST2", name: "Test Stock EUR")
+    trade = Trade.new(security: security, qty: 100, price: 1.5, currency: "EUR")
+    trade.exchange_rate = 1.1
+    @account.entries.create!(
+      name: "Buy 100 TEST2",
+      date: Date.new(2026, 5, 8),
+      amount: 150.00,
+      currency: "EUR",
+      entryable: trade
+    )
+
+    IbkrAccount::HistoricalBalancesSync.new(@ibkr_account).sync!
+
+    day2 = @account.balances.find_by!(date: Date.new(2026, 5, 8), currency: "CHF")
+    assert_in_delta 35.0, day2.net_market_flows.to_f, 0.01
+    assert_equal BigDecimal("2700.00"), day2.end_non_cash_balance
+  end
+
+  test "excludes balance row from upsert when Money::ConversionError prevents FX conversion" do
+    # EUR trade with no exchange_rate stored → custom_rate=nil → ConversionError raised.
+    # The affected date is excluded from the upsert entirely so net_market_flows is not
+    # silently wrong (the trade's value would otherwise flow into market appreciation).
+    # The seeded day2 balance is intentionally different from IBKR's total (3150 vs 3200)
+    # so we can assert the row was not overwritten by sync.
+    @ibkr_account.update!(
+      raw_equity_summary_payload: [
+        { report_date: "2026-05-07", total: "3000.00" },
+        { report_date: "2026-05-08", total: "3200.00" }
+      ]
+    )
+    seed_balance(date: Date.new(2026, 5, 7), balance: 3000.00, cash_balance: 500.00)
+    seed_balance(date: Date.new(2026, 5, 8), balance: 3150.00, cash_balance: 500.00)
+
+    security = Security.create!(ticker: "NORATE", name: "No Rate EUR Stock")
+    @account.entries.create!(
+      name: "Buy 100 NORATE",
+      date: Date.new(2026, 5, 8),
+      amount: 150.00,
+      currency: "EUR",
+      entryable: Trade.new(security: security, qty: 100, price: 1.5, currency: "EUR")
+    )
+
+    Money.any_instance.stubs(:exchange_to).raises(
+      Money::ConversionError.new(from_currency: "EUR", to_currency: "CHF", date: Date.new(2026, 5, 8))
+    )
+
+    IbkrAccount::HistoricalBalancesSync.new(@ibkr_account).sync!
+
+    # Day 1 is unaffected — still synced normally
+    day1 = @account.balances.find_by!(date: Date.new(2026, 5, 7), currency: "CHF")
+    assert_equal BigDecimal("3000.00"), day1.balance
+
+    # Day 2 was excluded from the upsert — seeded values are preserved, not overwritten
+    day2 = @account.balances.find_by!(date: Date.new(2026, 5, 8), currency: "CHF")
+    assert_equal BigDecimal("3150.00"), day2.balance          # seeded, not IBKR's 3200
+    assert_equal BigDecimal("0"),       day2.net_market_flows  # seeded, not recomputed
+  end
+
+  test "net_market_flows equals full non_cash delta when account has no trades" do
+    @ibkr_account.update!(
+      raw_equity_summary_payload: [
+        { report_date: "2026-05-07", total: "3000.00" },
+        { report_date: "2026-05-08", total: "3300.00" }
+      ]
+    )
+    seed_balance(date: Date.new(2026, 5, 7), balance: 3000.00, cash_balance: 500.00)
+    seed_balance(date: Date.new(2026, 5, 8), balance: 3300.00, cash_balance: 500.00)
+
+    IbkrAccount::HistoricalBalancesSync.new(@ibkr_account).sync!
+
+    day1 = @account.balances.find_by!(date: Date.new(2026, 5, 7), currency: "CHF")
+    day2 = @account.balances.find_by!(date: Date.new(2026, 5, 8), currency: "CHF")
+
+    assert_equal BigDecimal("0"),   day1.net_market_flows
+    assert_equal BigDecimal("300"), day2.net_market_flows
+    assert_equal BigDecimal("2800.00"), day2.end_non_cash_balance
+  end
+
+  test "sell trades reduce net_buy_sell so market loss is isolated in net_market_flows" do
+    # Day 1: total=3000, cash=500, non_cash=2500
+    # Day 2: total=2700, cash=700, non_cash=2000 (Δnon_cash=-500)
+    #   Sell 100 at CHF 1.50: entry.amount=-150 (negative = proceeds received)
+    #   net_buy_sell=-150; nmf = -500 - (-150) = -350 (market caused -350 loss)
+    @ibkr_account.update!(
+      raw_equity_summary_payload: [
+        { report_date: "2026-05-07", total: "3000.00" },
+        { report_date: "2026-05-08", total: "2700.00" }
+      ]
+    )
+    seed_balance(date: Date.new(2026, 5, 7), balance: 3000.00, cash_balance: 500.00)
+    seed_balance(date: Date.new(2026, 5, 8), balance: 2700.00, cash_balance: 700.00)
+
+    security = Security.create!(ticker: "SELL_TEST", name: "Sell Test Stock")
+    @account.entries.create!(
+      name: "Sell 100 SELL_TEST",
+      date: Date.new(2026, 5, 8),
+      amount: -150.00,
+      currency: "CHF",
+      entryable: Trade.new(security: security, qty: -100, price: 1.5, currency: "CHF")
+    )
+
+    IbkrAccount::HistoricalBalancesSync.new(@ibkr_account).sync!
+
+    day2 = @account.balances.find_by!(date: Date.new(2026, 5, 8), currency: "CHF")
+    assert_equal BigDecimal("-350"), day2.net_market_flows
+    assert_equal BigDecimal("2000.00"), day2.end_non_cash_balance
+  end
+
   test "writes balance row with zero total for fully liquidated dates" do
     @ibkr_account.update!(
       raw_equity_summary_payload: [