From cdc103d60d59ae2da861c9c4dbe93449366de452 Mon Sep 17 00:00:00 2001
From: Andrea Bugeja <25248102+arogan178@users.noreply.github.com>
Date: Mon, 19 Oct 2026 12:20:41 +0200
Subject: [PATCH] Fix historical conversion of derived currencies via root
 currency

---
 CHANGELOG.md                                  |  4 ++
 .../exchange-rate-data.service.spec.ts        | 69 +++++++++++++++++++
 .../exchange-rate-data.service.ts             | 29 ++++++--
 3 files changed, 98 insertions(+), 4 deletions(-)
 create mode 100644 apps/api/src/services/exchange-rate-data/exchange-rate-data.service.spec.ts

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7e35621f0b..920937dec9 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -15,6 +15,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Improved the performance of the historical market data table of the admin control panel by loading only the latest market price per asset profile
 - Introduced a cooldown of 12 hours for the asset profile and exchange rate gathering on activity creation by retaining the completed jobs
 
+### Fixed
+
+- Fixed the historical currency conversion of derived currencies (e.g. `GBp`) by converting via their root currency
+
 ## 3.88.0 - 2026-10-17
 
 ### Added
diff --git a/apps/api/src/services/exchange-rate-data/exchange-rate-data.service.spec.ts b/apps/api/src/services/exchange-rate-data/exchange-rate-data.service.spec.ts
new file mode 100644
index 0000000000..4e7e89f18f
--- /dev/null
+++ b/apps/api/src/services/exchange-rate-data/exchange-rate-data.service.spec.ts
@@ -0,0 +1,69 @@
+import { DataProviderService } from '@ghostfolio/api/services/data-provider/data-provider.service';
+import { MarketDataService } from '@ghostfolio/api/services/market-data/market-data.service';
+import { parseDate } from '@ghostfolio/common/helper';
+
+import { DataSource } from '@prisma/client';
+
+import { ExchangeRateDataService } from './exchange-rate-data.service';
+
+describe('ExchangeRateDataService', () => {
+  const date = parseDate('2026-01-02');
+  let exchangeRateDataService: ExchangeRateDataService;
+
+  beforeEach(() => {
+    // Only the root currency pairs exist, no derived pairs like USDGBp
+    const marketPrices: { [symbol: string]: number } = {
+      USDEUR: 0.9,
+      USDGBP: 0.8
+    };
+
+    exchangeRateDataService = new ExchangeRateDataService(
+      {
+        getDataSourceForExchangeRates: () => {
+          return DataSource.YAHOO;
+        }
+      } as unknown as DataProviderService,
+      {
+        get: jest.fn(({ symbol }: { symbol: string }) => {
+          return Promise.resolve(
+            marketPrices[symbol] ? { marketPrice: marketPrices[symbol] } : null
+          );
+        })
+      } as unknown as MarketDataService,
+      null,
+      null
+    );
+  });
+
+  describe('toCurrencyAtDate', () => {
+    it('converts a derived currency to its root currency', async () => {
+      await expect(
+        exchangeRateDataService.toCurrencyAtDate(1000, 'GBp', 'GBP', date)
+      ).resolves.toBeCloseTo(10);
+    });
+
+    it('converts a root currency to its derived currency', async () => {
+      await expect(
+        exchangeRateDataService.toCurrencyAtDate(10, 'GBP', 'GBp', date)
+      ).resolves.toBeCloseTo(1000);
+    });
+
+    it('converts a derived currency indirectly via the root currency', async () => {
+      await expect(
+        exchangeRateDataService.toCurrencyAtDate(8000, 'GBp', 'EUR', date)
+      ).resolves.toBeCloseTo(90);
+    });
+
+    it('converts to a derived currency indirectly via the root currency', async () => {
+      await expect(
+        exchangeRateDataService.toCurrencyAtDate(90, 'EUR', 'GBp', date)
+      ).resolves.toBeCloseTo(8000);
+    });
+
+    it('keeps the value of the same derived currency', async () => {
+      await expect(
+        exchangeRateDataService.toCurrencyAtDate(1.15, 'GBp', 'GBp', date)
+      ).resolves.toBe(1.15);
+    });
+  });
+});
diff --git a/apps/api/src/services/exchange-rate-data/exchange-rate-data.service.ts b/apps/api/src/services/exchange-rate-data/exchange-rate-data.service.ts
index b68ed2fb15..c0b0751426 100644
--- a/apps/api/src/services/exchange-rate-data/exchange-rate-data.service.ts
+++ b/apps/api/src/services/exchange-rate-data/exchange-rate-data.service.ts
@@ -296,18 +296,39 @@ export class ExchangeRateDataService {
       return 0;
     }
 
+    const derivedFromCurrency = DERIVED_CURRENCIES.find(({ currency }) => {
+      return currency === aFromCurrency;
+    });
+    const derivedToCurrency = DERIVED_CURRENCIES.find(({ currency }) => {
+      return currency === aToCurrency;
+    });
+
+    if (
+      aFromCurrency !== aToCurrency &&
+      (derivedFromCurrency || derivedToCurrency)
+    ) {
+      // Convert via the root currencies, since the exchange rates of derived
+      // currencies are not available for every currency pair
+      const valueInRootCurrency = await this.toCurrencyAtDate(
+        aValue / (derivedFromCurrency?.factor ?? 1),
+        derivedFromCurrency?.rootCurrency ?? aFromCurrency,
+        derivedToCurrency?.rootCurrency ?? aToCurrency,
+        aDate
+      );
+
+      return valueInRootCurrency === undefined
+        ? undefined
+        : valueInRootCurrency * (derivedToCurrency?.factor ?? 1);
+    }
+
     if (isToday(aDate)) {
       return this.toCurrency(aValue, aFromCurrency, aToCurrency);
     }
 
-    const derivedCurrencyFactor =
-      this.derivedCurrencyFactors[`${aFromCurrency}${aToCurrency}`];
     let factor: number;
 
     if (aFromCurrency === aToCurrency) {
       factor = 1;
-    } else if (derivedCurrencyFactor) {
-      factor = derivedCurrencyFactor;
     } else {
       const dataSource =
         this.dataProviderService.getDataSourceForExchangeRates();