diff --git a/test/api/v3/integration/tasks/PUT-tasks_id.test.js b/test/api/v3/integration/tasks/PUT-tasks_id.test.js
index ef50ad8db4..f7ffa638b3 100644
--- a/test/api/v3/integration/tasks/PUT-tasks_id.test.js
+++ b/test/api/v3/integration/tasks/PUT-tasks_id.test.js
@@ -499,6 +499,45 @@ describe('PUT /tasks/:id', () => {
     });
   });
 
+  context('monthly dailys', () => {
+    let monthly;
+
+    beforeEach(async () => {
+      const date1 = moment.utc('2020-07-01').toDate();
+      monthly = await user.post('/tasks/user', {
+        text: 'test monthly',
+        type: 'daily',
+        frequency: 'monthly',
+        startDate: date1,
+        daysOfMonth: [date1.getDate()],
+      });
+    });
+
+    it('updates days of month when start date updated', async () => {
+      const date2 = moment.utc('2020-07-01').toDate();
+      const savedMonthly = await user.put(`/tasks/${monthly._id}`, {
+        startDate: date2,
+      });
+
+      expect(savedMonthly.daysOfMonth).to.deep.equal([moment(date2).date()]);
+    });
+
+    it('updates next due when start date updated', async () => {
+      const date2 = moment.utc('2020-07-01').toDate();
+      const savedMonthly = await user.put(`/tasks/${monthly._id}`, {
+        startDate: date2,
+      });
+
+      expect(savedMonthly.nextDue.length).to.eql(6);
+      expect(moment(savedMonthly.nextDue[0]).toDate()).to.eql(moment.utc('2020-08-01').toDate());
+      expect(moment(savedMonthly.nextDue[1]).toDate()).to.eql(moment.utc('2020-09-01').toDate());
+      expect(moment(savedMonthly.nextDue[2]).toDate()).to.eql(moment.utc('2020-10-01').toDate());
+      expect(moment(savedMonthly.nextDue[3]).toDate()).to.eql(moment.utc('2020-11-01').toDate());
+      expect(moment(savedMonthly.nextDue[4]).toDate()).to.eql(moment.utc('2020-12-01').toDate());
+      expect(moment(savedMonthly.nextDue[5]).toDate()).to.eql(moment.utc('2021-01-01').toDate());
+    });
+  });
+
   context('rewards', () => {
     let reward;
 
diff --git a/website/server/controllers/api-v3/tasks.js b/website/server/controllers/api-v3/tasks.js
index 159cabadac..646c473e10 100644
--- a/website/server/controllers/api-v3/tasks.js
+++ b/website/server/controllers/api-v3/tasks.js
@@ -681,6 +681,15 @@ api.updateTask = {
       task.group.managerNotes = sanitizedObj.managerNotes;
     }
 
+    // If the task was set to repeat monthly on a day of the month, and the start date was updated,
+    // the task will then need to be updated to repeat on the same day of the month as the new
+    // start date. For example, if the start date is updated to 7/2/2020, the daily should
+    // repeat on the 2nd day of the month. It's possible that a task can repeat monthly on a
+    // week of the month, in which case we won't update the repetition at all.
+    if (task.frequency === 'monthly' && task.daysOfMonth.length && task.startDate) {
+      task.daysOfMonth = [moment(task.startDate).date()];
+    }
+
     setNextDue(task, user);
     const savedTask = await task.save();