diff --git a/src/services/dateChart.service.spec.ts b/src/services/dateChart.service.spec.ts
index c261baf9ef0a774fef5158a03a58fff5e079101c..f7bfff65968b2821202d48daa2781a61f4d67a8e 100644
--- a/src/services/dateChart.service.spec.ts
+++ b/src/services/dateChart.service.spec.ts
@@ -1111,20 +1111,6 @@ describe('dateChart service', () => {
       )
       expect(result).toEqual(1)
     })
-    it('should return index -1 for year, 2024', () => {
-      const selectedDate: DateTime = DateTime.fromISO(
-        '2024-01-01T00:00:00.000Z',
-        {
-          zone: 'utc',
-        }
-      )
-      const result = dateChartService.defineDateIndex(
-        TimeStep.YEAR,
-        selectedDate
-      )
-      expect(result).toEqual(-1)
-    })
-
     it('should return index 0 for month, 05-2020', () => {
       const selectedDate: DateTime = DateTime.fromISO(
         '2020-05-01T00:00:00.000Z',
diff --git a/src/services/dateChart.service.ts b/src/services/dateChart.service.ts
index 550252fa28d5b5ff031982636a70f8142ed14893..efd5334464e2cad9eece21351337a38196d4bd93 100644
--- a/src/services/dateChart.service.ts
+++ b/src/services/dateChart.service.ts
@@ -256,10 +256,10 @@ export default class DateChartService {
   }
 
   /**
-   * Return the date incremented in function of the timestep
+   * Return the chart index in function of the timestep and a given date
    * @param {TimeStep} timeStep - current time step
    * @param {DateTime} selectedDate - current selected date
-   * @returns {number} - incremented date
+   * @returns {number} - index
    */
   public defineDateIndex(timeStep: TimeStep, selectedDate: DateTime): number {
     const today = DateTime.local().setZone('utc', {
@@ -267,11 +267,7 @@ export default class DateChartService {
     })
     switch (timeStep) {
       case TimeStep.YEAR:
-        if (today.year >= selectedDate.year) {
-          return Math.trunc((today.year - selectedDate.year) / 5)
-        } else {
-          return Math.trunc((today.year - selectedDate.year) / 5) - 1
-        }
+        return Math.trunc((today.year - selectedDate.year) / 5)
       case TimeStep.MONTH:
         return today.year - selectedDate.year
       case TimeStep.DAY: