diff --git a/app/services/grade_service.ts b/app/services/grade_service.ts
index 16191e3..3724fcb 100644
--- a/app/services/grade_service.ts
+++ b/app/services/grade_service.ts
@@ -112,7 +112,7 @@ export class GradeService {
 
     while (periodStartDate < startDate.plus({ months })) {
       const periodEndDate = periodStartDate.endOf('month')
-      const periodColles = this.getPeriodColles(colles, startDate, periodEndDate)
+      const periodColles = this.getPeriodColles(colles, periodStartDate, periodEndDate)
 
       const periodAverage = this.calculateAverage(periodColles)
       const subjectAverages = await this.getSubjectAverages(