diff --git a/CHANGELOG.md b/CHANGELOG.md
index bb13ba072..35560bf95 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -18,6 +18,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 
+- Improved the time-weighted performance calculation for `1D`
 - Improved the tabs on iOS (_Add to Home Screen_)
 
 ## 2.33.0 - 2023-12-31
diff --git a/apps/api/src/app/portfolio/portfolio-calculator.ts b/apps/api/src/app/portfolio/portfolio-calculator.ts
index 06a5ca6ae..71ddbb6dd 100644
--- a/apps/api/src/app/portfolio/portfolio-calculator.ts
+++ b/apps/api/src/app/portfolio/portfolio-calculator.ts
@@ -1246,7 +1246,7 @@ export class PortfolioCalculator {
       if (i > indexOfStartOrder) {
         // Only consider periods with an investment for the calculation of
         // the time weighted investment
-        if (totalInvestmentBeforeTransaction.gt(0)) {
+        if (valueOfInvestmentBeforeTransaction.gt(0)) {
           // Calculate the number of days since the previous order
           const orderDate = new Date(order.date);
           const previousOrderDate = new Date(orders[i - 1].date);
@@ -1267,7 +1267,10 @@ export class PortfolioCalculator {
           totalInvestmentDays += daysSinceLastOrder;
 
           sumOfTimeWeightedInvestments = sumOfTimeWeightedInvestments.add(
-            totalInvestmentBeforeTransaction.mul(daysSinceLastOrder)
+            valueAtStartDate
+              .minus(investmentAtStartDate)
+              .plus(totalInvestmentBeforeTransaction)
+              .mul(daysSinceLastOrder)
           );
         }
 
diff --git a/apps/api/src/app/portfolio/portfolio.service.ts b/apps/api/src/app/portfolio/portfolio.service.ts
index 050559c85..cd4fa0bae 100644
--- a/apps/api/src/app/portfolio/portfolio.service.ts
+++ b/apps/api/src/app/portfolio/portfolio.service.ts
@@ -1035,25 +1035,44 @@ export class PortfolioService {
 
     return {
       hasErrors: currentPositions.hasErrors,
-      positions: positions.map((position) => {
-        return {
-          ...position,
-          assetClass: symbolProfileMap[position.symbol].assetClass,
-          assetSubClass: symbolProfileMap[position.symbol].assetSubClass,
-          averagePrice: new Big(position.averagePrice).toNumber(),
-          grossPerformance: position.grossPerformance?.toNumber() ?? null,
-          grossPerformancePercentage:
-            position.grossPerformancePercentage?.toNumber() ?? null,
-          investment: new Big(position.investment).toNumber(),
-          marketState:
-            dataProviderResponses[position.symbol]?.marketState ?? 'delayed',
-          name: symbolProfileMap[position.symbol].name,
-          netPerformance: position.netPerformance?.toNumber() ?? null,
-          netPerformancePercentage:
-            position.netPerformancePercentage?.toNumber() ?? null,
-          quantity: new Big(position.quantity).toNumber()
-        };
-      })
+      positions: positions.map(
+        ({
+          averagePrice,
+          currency,
+          dataSource,
+          firstBuyDate,
+          investment,
+          grossPerformance,
+          grossPerformancePercentage,
+          netPerformance,
+          netPerformancePercentage,
+          quantity,
+          symbol,
+          transactionCount
+        }) => {
+          return {
+            currency,
+            dataSource,
+            firstBuyDate,
+            symbol,
+            transactionCount,
+            assetClass: symbolProfileMap[symbol].assetClass,
+            assetSubClass: symbolProfileMap[symbol].assetSubClass,
+            averagePrice: averagePrice.toNumber(),
+            grossPerformance: grossPerformance?.toNumber() ?? null,
+            grossPerformancePercentage:
+              grossPerformancePercentage?.toNumber() ?? null,
+            investment: investment.toNumber(),
+            marketState:
+              dataProviderResponses[symbol]?.marketState ?? 'delayed',
+            name: symbolProfileMap[symbol].name,
+            netPerformance: netPerformance?.toNumber() ?? null,
+            netPerformancePercentage:
+              netPerformancePercentage?.toNumber() ?? null,
+            quantity: quantity.toNumber()
+          };
+        }
+      )
     };
   }