diff --git a/apps/api/src/app/portfolio/portfolio-calculator.ts b/apps/api/src/app/portfolio/portfolio-calculator.ts
index f6b695603..8ac2ba781 100644
--- a/apps/api/src/app/portfolio/portfolio-calculator.ts
+++ b/apps/api/src/app/portfolio/portfolio-calculator.ts
@@ -1269,9 +1269,7 @@ export class PortfolioCalculator {
     }
 
     const averageInvestmentBetweenStartAndEndDate = getAverage(
-      Object.values(investmentValues).map((investmentValue) => {
-        return investmentValue.toNumber();
-      })
+      Object.values(investmentValues)
     );
 
     const totalGrossPerformance = grossPerformance.minus(
@@ -1286,7 +1284,7 @@ export class PortfolioCalculator {
       averagePriceAtStartDate.eq(0) ||
       averagePriceAtEndDate.eq(0) ||
       orders[indexOfStartOrder].unitPrice.eq(0)
-        ? averageInvestmentBetweenStartAndEndDate > 0
+        ? averageInvestmentBetweenStartAndEndDate.gt(0)
           ? totalGrossPerformance.div(averageInvestmentBetweenStartAndEndDate)
           : new Big(0)
         : // This formula has the issue that buying more units with a price
@@ -1307,7 +1305,7 @@ export class PortfolioCalculator {
       averagePriceAtStartDate.eq(0) ||
       averagePriceAtEndDate.eq(0) ||
       orders[indexOfStartOrder].unitPrice.eq(0)
-        ? averageInvestmentBetweenStartAndEndDate > 0
+        ? averageInvestmentBetweenStartAndEndDate.gt(0)
           ? totalNetPerformance.div(averageInvestmentBetweenStartAndEndDate)
           : new Big(0)
         : // This formula has the issue that buying more units with a price
diff --git a/libs/common/src/lib/helper.ts b/libs/common/src/lib/helper.ts
index 868a22e7d..150a5b0a6 100644
--- a/libs/common/src/lib/helper.ts
+++ b/libs/common/src/lib/helper.ts
@@ -133,8 +133,12 @@ export function getAssetProfileIdentifier({ dataSource, symbol }: UniqueAsset) {
   return `${dataSource}-${symbol}`;
 }
 
-export function getAverage(aArray: number[]) {
-  return aArray.reduce((a, b) => a + b, 0) / aArray.length;
+export function getAverage(aArray: Big[]) {
+  if (aArray?.length > 0) {
+    return aArray.reduce((a, b) => a.plus(b), new Big(0)).div(aArray.length);
+  }
+
+  return new Big(0);
 }
 
 export function getBackgroundColor(aColorScheme: ColorScheme) {