diff --git a/src/utils/common-expression-helpers.test.ts b/src/utils/common-expression-helpers.test.ts
index 0397b19a..c2f126f6 100644
--- a/src/utils/common-expression-helpers.test.ts
+++ b/src/utils/common-expression-helpers.test.ts
@@ -171,7 +171,7 @@ describe('CommonExpressionHelpers', () => {
     it('should return the correct number of months on ART', () => {
       const artStartDate = new Date('2020-01-01');
       const today = new Date();
-      const monthsOnART = Math.floor((today.getTime() - artStartDate.getTime()) / (1000 * 60 * 60 * 24 * 30));
+      const monthsOnART = dayjs(today).diff(dayjs(artStartDate), 'months');
       expect(helpers.calcMonthsOnART(artStartDate)).toBe(monthsOnART);
     });
 
diff --git a/src/utils/common-expression-helpers.ts b/src/utils/common-expression-helpers.ts
index caf6df9c..c4a4b64d 100644
--- a/src/utils/common-expression-helpers.ts
+++ b/src/utils/common-expression-helpers.ts
@@ -118,19 +118,22 @@ export class CommonExpressionHelpers {
   };
 
   calcMonthsOnART = (artStartDate: Date) => {
-    if (artStartDate == null) return null;
+    if (artStartDate == null) {
+      return null;
+    }
 
     if (!(artStartDate instanceof Date)) {
       throw new Error('DateFormatException: value passed is not a valid date');
     }
 
-    let today = new Date();
-    let resultMonthsOnART: number;
-    let artInDays = Math.round((today.getTime() - artStartDate.getTime?.()) / 86400000);
-    if (artStartDate && artInDays >= 30) {
-      resultMonthsOnART = Math.floor(artInDays / 30);
+    const today = new Date();
+    const artInDays = Math.round((today.getTime() - artStartDate.getTime()) / 86400000);
+
+    if (artInDays < 30) {
+      return 0;
     }
-    return artStartDate ? resultMonthsOnART : null;
+
+    return dayjs(today).diff(artStartDate, 'month');
   };
 
   calcViralLoadStatus = (viralLoadCount: number) => {