diff --git a/src/components/charts/MonthChart/formatMonthData.ts b/src/components/charts/MonthChart/formatMonthData.ts
index b0a98ac4..9ccf5545 100644
--- a/src/components/charts/MonthChart/formatMonthData.ts
+++ b/src/components/charts/MonthChart/formatMonthData.ts
@@ -1,4 +1,11 @@
-import { addWeeks, getDaysInMonth, getWeeksInMonth, isSameWeek, startOfMonth } from 'date-fns';
+import {
+  addWeeks,
+  getDay,
+  getDaysInMonth,
+  getWeeksInMonth,
+  isSameWeek,
+  startOfMonth
+} from 'date-fns';
 import TrackerEntry from '../../../models/TrackerEntry';
 import { getAggregatedCompletions } from '../../../store/trackers/utils';
 import { DataType } from './types';
@@ -9,10 +16,14 @@ const formatData = (monthDate: Date, entries: TrackerEntry[]): DataType[] => {
   const startDay = startOfMonth(monthDate);
   for (let i = 0; i < nbOfWeeks; i += 1) {
     const week = addWeeks(startDay, i);
+    const weekBeginDayNumber = i === 0 ? 1 : i * 7 + 1;
+    const weekEndDayNumber = Math.min(i * 7 + 7, getDaysInMonth(startDay));
     const weekData: DataType = {
-      name: (i === 0 ? 1 : i * 7 + 1) + '-' + Math.min(i * 7 + 8, getDaysInMonth(startDay))
+      name: weekBeginDayNumber + '-' + weekEndDayNumber
     };
-    const weekEntries = entries.filter((e) => isSameWeek(new Date(e.date), week));
+    const weekEntries = entries.filter((e) => isSameWeek(new Date(e.date), week), {
+      weekStartsOn: getDay(new Date(week))
+    });
     const aggCompletions = getAggregatedCompletions(weekEntries);
     aggCompletions.forEach((c) => {
       weekData[c.unit] = c.quantity;