diff --git a/apps/api/src/app/portfolio/portfolio.service.spec.ts b/apps/api/src/app/portfolio/portfolio.service.spec.ts
index c398d6a28..b503b18e9 100644
--- a/apps/api/src/app/portfolio/portfolio.service.spec.ts
+++ b/apps/api/src/app/portfolio/portfolio.service.spec.ts
@@ -606,5 +606,67 @@ describe('PortfolioService', () => {
 
       expect(accounts[account.id].quantity).toBeUndefined();
     });
+
+    it('should only consider accounts of the current user if the activities are filtered by a single account', async () => {
+      const accountsSpy = jest.spyOn(accountService, 'accounts');
+
+      await getValueOfAccountsAndPlatforms({
+        activities: [],
+        filters: [{ id: account.id, type: 'ACCOUNT' }],
+        portfolioItemsNow: {},
+        userCurrency: 'USD',
+        userId: userDummyData.id
+      });
+
+      expect(accountsSpy).toHaveBeenCalledWith(
+        expect.objectContaining({
+          where: { userId: userDummyData.id, id: account.id }
+        })
+      );
+    });
+
+    it('should exclude the cash balance if the activities are filtered by a single holding', async () => {
+      const { accounts, platforms } = await getValueOfAccountsAndPlatforms({
+        activities: [
+          {
+            account,
+            accountId: account.id,
+            assetProfile: { symbol: 'AAPL' },
+            quantity: 1,
+            type: 'BUY'
+          }
+        ],
+        filters: [{ id: 'AAPL', type: 'SYMBOL' }],
+        portfolioItemsNow: {
+          AAPL: { marketPriceInBaseCurrency: 10 }
+        },
+        userCurrency: 'USD',
+        userId: userDummyData.id
+      });
+
+      // 1 * 10 (activity), without the balance of 100
+      expect(accounts[account.id].valueInBaseCurrency).toBe(10);
+      expect(platforms[account.platformId].valueInBaseCurrency).toBe(10);
+    });
+
+    it('should not accumulate rounding errors of the balances of accounts sharing a platform', async () => {
+      const platformId = randomUUID();
+
+      jest.spyOn(accountService, 'getAccounts').mockResolvedValue([
+        { ...account, platformId, balance: 0.1, id: randomUUID() },
+        { ...account, platformId, balance: 0.2, id: randomUUID() }
+      ] as unknown as AccountWithBalance[]);
+
+      const { platforms } = await getValueOfAccountsAndPlatforms({
+        activities: [],
+        filters: [],
+        portfolioItemsNow: {},
+        userCurrency: 'USD',
+        userId: userDummyData.id
+      });
+
+      // 0.1 (balance) + 0.2 (balance)
+      expect(platforms[platformId].valueInBaseCurrency).toBe(0.3);
+    });
   });
 });
diff --git a/apps/api/src/app/portfolio/portfolio.service.ts b/apps/api/src/app/portfolio/portfolio.service.ts
index 1ec3dd234..25e79ceff 100644
--- a/apps/api/src/app/portfolio/portfolio.service.ts
+++ b/apps/api/src/app/portfolio/portfolio.service.ts
@@ -2214,7 +2214,7 @@ export class PortfolioService {
     } else if (filters.length === 1 && filters[0].type === 'ACCOUNT') {
       currentAccounts = await this.accountService.accounts({
         include: { platform: true, tags: true },
-        where: { id: filters[0].id }
+        where: { userId, id: filters[0].id }
       });
     } else {
       const accountIds = Array.from(
@@ -2242,39 +2242,43 @@ export class PortfolioService {
     // Iterate over the accounts plus a null entry to group activities without
     // an account into the unknown bucket
     for (const account of [...currentAccounts, null]) {
+      const currentAccountId = account?.id || UNKNOWN_KEY;
+      const currentPlatformId = account?.platformId || UNKNOWN_KEY;
+
       const ordersByAccount = activities.filter(({ accountId }) => {
         return account ? accountId === account.id : !accountId;
       });
 
       if (account) {
-        accounts[account.id] = {
+        // The cash balance is not part of a holding and would distort the value
+        // and thus the allocation per account and platform
+        const balanceInBaseCurrency = filterBySymbol
+          ? 0
+          : this.exchangeRateDataService.toCurrency(
+              account.balance,
+              account.currency,
+              userCurrency
+            );
+
+        accounts[currentAccountId] = {
           balance: account.balance,
           currency: account.currency,
           name: account.name,
-          valueInBaseCurrency: this.exchangeRateDataService.toCurrency(
-            account.balance,
-            account.currency,
-            userCurrency
-          )
+          valueInBaseCurrency: balanceInBaseCurrency
         };
 
-        if (platforms[account.platformId || UNKNOWN_KEY]?.valueInBaseCurrency) {
-          platforms[account.platformId || UNKNOWN_KEY].valueInBaseCurrency +=
-            this.exchangeRateDataService.toCurrency(
-              account.balance,
-              account.currency,
-              userCurrency
-            );
+        if (platforms[currentPlatformId]) {
+          platforms[currentPlatformId].valueInBaseCurrency = new Big(
+            platforms[currentPlatformId].valueInBaseCurrency
+          )
+            .plus(balanceInBaseCurrency)
+            .toNumber();
         } else {
-          platforms[account.platformId || UNKNOWN_KEY] = {
+          platforms[currentPlatformId] = {
             balance: account.balance,
             currency: account.currency,
             name: account.platform?.name,
-            valueInBaseCurrency: this.exchangeRateDataService.toCurrency(
-              account.balance,
-              account.currency,
-              userCurrency
-            )
+            valueInBaseCurrency: balanceInBaseCurrency
           };
         }
       }
@@ -2299,9 +2303,6 @@ export class PortfolioService {
         );
       }
 
-      const currentAccountId = account?.id || UNKNOWN_KEY;
-      const currentPlatformId = account?.platformId || UNKNOWN_KEY;
-
       // The quantity is only meaningful if the activities are filtered by a
       // single holding
       const quantityOfHolding = filterBySymbol