diff --git a/CHANGELOG.md b/CHANGELOG.md
index 87b393347..460310451 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+### Added
+
+- Added `accountId` and `date` as a unique constraint to the `AccountBalance` database schema
+
 ### Fixed
 
 - Fixed an issue with `totalValueInBaseCurrency` in the value redaction interceptor for the impersonation mode
diff --git a/apps/api/src/app/account-balance/account-balance.controller.ts b/apps/api/src/app/account-balance/account-balance.controller.ts
index 12f21753b..4a8412003 100644
--- a/apps/api/src/app/account-balance/account-balance.controller.ts
+++ b/apps/api/src/app/account-balance/account-balance.controller.ts
@@ -1,6 +1,7 @@
 import { AccountService } from '@ghostfolio/api/app/account/account.service';
 import { HasPermission } from '@ghostfolio/api/decorators/has-permission.decorator';
 import { HasPermissionGuard } from '@ghostfolio/api/guards/has-permission.guard';
+import { resetHours } from '@ghostfolio/common/helper';
 import { permissions } from '@ghostfolio/common/permissions';
 import type { RequestWithUser } from '@ghostfolio/common/types';
 
@@ -17,6 +18,7 @@ import {
 import { REQUEST } from '@nestjs/core';
 import { AuthGuard } from '@nestjs/passport';
 import { AccountBalance } from '@prisma/client';
+import { parseISO } from 'date-fns';
 import { StatusCodes, getReasonPhrase } from 'http-status-codes';
 
 import { AccountBalanceService } from './account-balance.service';
@@ -50,17 +52,11 @@ export class AccountBalanceController {
       );
     }
 
-    return this.accountBalanceService.createAccountBalance({
-      Account: {
-        connect: {
-          id_userId: {
-            id: account.id,
-            userId: account.userId
-          }
-        }
-      },
+    return this.accountBalanceService.createOrUpdateAccountBalance({
+      accountId: account.id,
+      balance: data.balance,
       date: data.date,
-      value: data.balance
+      userId: account.userId
     });
   }
 
diff --git a/apps/api/src/app/account-balance/account-balance.service.ts b/apps/api/src/app/account-balance/account-balance.service.ts
index 8a9d7b83e..5a5ec5be0 100644
--- a/apps/api/src/app/account-balance/account-balance.service.ts
+++ b/apps/api/src/app/account-balance/account-balance.service.ts
@@ -1,10 +1,14 @@
 import { ExchangeRateDataService } from '@ghostfolio/api/services/exchange-rate-data/exchange-rate-data.service';
 import { PrismaService } from '@ghostfolio/api/services/prisma/prisma.service';
+import { resetHours } from '@ghostfolio/common/helper';
 import { AccountBalancesResponse, Filter } from '@ghostfolio/common/interfaces';
 import { UserWithSettings } from '@ghostfolio/common/types';
 
 import { Injectable } from '@nestjs/common';
 import { AccountBalance, Prisma } from '@prisma/client';
+import { parseISO } from 'date-fns';
+
+import { CreateAccountBalanceDto } from './create-account-balance.dto';
 
 @Injectable()
 export class AccountBalanceService {
@@ -24,11 +28,36 @@ export class AccountBalanceService {
     });
   }
 
-  public async createAccountBalance(
-    data: Prisma.AccountBalanceCreateInput
-  ): Promise<AccountBalance> {
-    return this.prismaService.accountBalance.create({
-      data
+  public async createOrUpdateAccountBalance({
+    accountId,
+    balance,
+    date,
+    userId
+  }: CreateAccountBalanceDto & {
+    userId: string;
+  }): Promise<AccountBalance> {
+    return this.prismaService.accountBalance.upsert({
+      create: {
+        Account: {
+          connect: {
+            id_userId: {
+              userId,
+              id: accountId
+            }
+          }
+        },
+        date: resetHours(parseISO(date)),
+        value: balance
+      },
+      update: {
+        value: balance
+      },
+      where: {
+        accountId_date: {
+          accountId,
+          date: resetHours(parseISO(date))
+        }
+      }
     });
   }
 
diff --git a/apps/api/src/app/account/account.service.ts b/apps/api/src/app/account/account.service.ts
index 697041645..fed1860cd 100644
--- a/apps/api/src/app/account/account.service.ts
+++ b/apps/api/src/app/account/account.service.ts
@@ -6,6 +6,7 @@ import { Filter } from '@ghostfolio/common/interfaces';
 import { Injectable } from '@nestjs/common';
 import { Account, Order, Platform, Prisma } from '@prisma/client';
 import { Big } from 'big.js';
+import { parseISO } from 'date-fns';
 import { groupBy } from 'lodash';
 
 import { CashDetails } from './interfaces/cash-details.interface';
@@ -242,17 +243,11 @@ export class AccountService {
       );
 
     if (amountInCurrencyOfAccount) {
-      await this.accountBalanceService.createAccountBalance({
-        date,
-        Account: {
-          connect: {
-            id_userId: {
-              userId,
-              id: accountId
-            }
-          }
-        },
-        value: new Big(balance).plus(amountInCurrencyOfAccount).toNumber()
+      await this.accountBalanceService.createOrUpdateAccountBalance({
+        accountId,
+        userId,
+        balance: new Big(balance).plus(amountInCurrencyOfAccount).toNumber(),
+        date: date.toISOString()
       });
     }
   }
diff --git a/prisma/migrations/20240421080039_added_account_id_and_date_to_account_balance_as_unique_constraint/migration.sql b/prisma/migrations/20240421080039_added_account_id_and_date_to_account_balance_as_unique_constraint/migration.sql
new file mode 100644
index 000000000..96521bbfa
--- /dev/null
+++ b/prisma/migrations/20240421080039_added_account_id_and_date_to_account_balance_as_unique_constraint/migration.sql
@@ -0,0 +1,29 @@
+-- Only keep the newest AccountBalance entry for each account / day
+WITH entries_to_keep AS (
+  SELECT
+    id,
+    "accountId",
+    date,
+    ROW_NUMBER() OVER (PARTITION BY "accountId", DATE(date) ORDER BY date DESC) AS row_num
+  FROM
+    "AccountBalance"
+),
+entries_to_delete AS (
+  SELECT
+    id
+  FROM
+    entries_to_keep
+  WHERE
+    row_num > 1
+)
+DELETE FROM
+  "AccountBalance"
+WHERE
+  id IN (SELECT id FROM entries_to_delete);
+
+-- Reset time part of the date
+UPDATE "AccountBalance"
+SET date = DATE_TRUNC('day', date);
+
+-- CreateIndex
+CREATE UNIQUE INDEX "AccountBalance_accountId_date_key" ON "AccountBalance"("accountId", "date");
diff --git a/prisma/schema.prisma b/prisma/schema.prisma
index f9a17d114..af7ad1845 100644
--- a/prisma/schema.prisma
+++ b/prisma/schema.prisma
@@ -59,6 +59,7 @@ model AccountBalance {
   value     Float
   Account   Account  @relation(fields: [accountId, userId], onDelete: Cascade, references: [id, userId])
 
+  @@unique([accountId, date])
   @@index([accountId])
   @@index([date])
 }