diff --git a/services/experimentAnalysis.ts b/services/experimentAnalysis.ts
index 4673f9d..99a5154 100644
--- a/services/experimentAnalysis.ts
+++ b/services/experimentAnalysis.ts
@@ -148,9 +148,10 @@ function aggregateWeeklyMetrics(
     const key = `${year}-W${String(weekNum).padStart(2, '0')}`;
 
     if (!weeklyMap.has(key)) {
+      // Use ISO week start (Monday) instead of Sunday for consistency
       weeklyMap.set(key, {
         week: key,
-        timestamp: getWeekStartSunday(year, weekNum),
+        timestamp: getISOWeekMonday(year, weekNum),
         units: 0,
         revenue: 0,
         adRevenue: 0,