Fix Microsoft To Do Not Syncing Across Devices

Applies to: Microsoft To Do, Microsoft 365, Outlook, Microsoft Teams, Windows, macOS, iOS, Android
Article Type: Troubleshooting
Last Updated: 2026-08-09

Summary

Microsoft To Do refreshes itself every few seconds without being asked, so when a task stops appearing on your other device there is nothing on screen explaining why. This article works through the six real causes in the order that resolves them fastest — starting with the one that accounts for most cases, which is not a sync failure at all but two devices signed in to two different accounts.

Symptoms

• A task added on your phone never appears on your laptop, or the other way round.
• A task you ticked off comes back un-completed a few minutes later.
• One list is days behind the same list on another device.
• A whole shared list disappeared from your sidebar overnight.
• A task you know you created is nowhere in To Do, but you can see it in Outlook.
• To Do shows It looks like a firewall is preventing your data from syncing, or the web version returns a 503 error at sign-in.

In this guide

• 1. Confirm Which Account the Task Was Added Under
• 2. Force the App to Pick Up Changes Now
• 3. Check Whether a Shared List Was Un-Shared
• 4. Look for the Task in Outlook and in the Planner App in Teams
• 5. Sign Out and Back In to Refresh an Expired Session
• 6. Clear What Is Blocking the Upload

Before You Start

• Microsoft To Do installed on at least two devices, or one device plus a browser.
• The email address of every account you use with To Do — personal and work. Step 1 depends on comparing them.
• No admin rights are needed for any step in this article. Nothing here uses the Registry, a command line, or an elevated prompt.

Instructions

1. Confirm Which Account the Task Was Added Under

Microsoft To Do keeps personal and work accounts in separate task stores, so a task added under one is genuinely absent from the other.

1. Open Microsoft To Do on the device where the task is missing.
2. Select your name or profile picture at the top of the left sidebar. The account panel opens and shows the email address of the account currently signed in.
3. Write that address down, then do the same on the device where the task does exist. Compare them character for character — [email protected] and [email protected] look almost identical in a small font.
4. If the two addresses differ, the task is not lost and nothing is broken. It is sitting in the other account's list, exactly where you put it.
5. On Windows and Android, add the second account rather than swapping between them: select your name at the top of the sidebar, select Add account, and follow the prompts. Both accounts then appear in that same panel, and you switch by selecting one. Microsoft documents multiple-account support on Android and Windows only.
6. On iPhone, iPad, Mac, and the web, sign out of the current account and sign back in with the other one to see its lists. Signing out removes nothing — your tasks live on Microsoft's servers, not on the device, and they download again the moment you sign back in.
7. You know this was the cause when the missing task appears in its list under the second account, with its due date and steps intact.

Note: A task cannot be moved between a personal and a work account by syncing, because the two are separate mailboxes. To bring one across, open the task in the account that has it, copy the title and any notes, and retype it in the account you want it in. If you are still setting up your lists, How to Use Microsoft To Do for Personal Task Management covers how the lists, My Day, and flagged emails fit together.

2. Force the App to Pick Up Changes Now

To Do polls for changes every few seconds, so restarting it proves whether you are looking at a delay or a real failure.

1. On the web: press Ctrl + R to reload the page (Cmd + R on a Mac). Your lists redraw from the server.
2. On Windows: close the Microsoft To Do window, then reopen it from the Start menu. The list pane repopulates as the app reconnects.
3. On a phone or tablet: close To Do completely from the app switcher rather than returning to the home screen, then open it again. An app left in the background can sit for a long time without reconnecting.
4. Leave the app open for a minute and watch the list. A task that has not arrived after a full minute on a working connection is not a timing problem — carry on to the next step.

Verification: Add a throwaway task named sync test on one device. It appears on the other within seconds. If it does, sync is healthy and the original missing task has a different cause — check step 1 again, then step 3.

3. Check Whether a Shared List Was Un-Shared

When a whole list vanishes rather than one task, its owner stopped sharing it — the tasks were never deleted, your access was.

1. Look at the left sidebar and confirm the whole list is gone, not one task inside it. A missing list is a sharing change; a missing task inside a list that is still there is not.
2. Contact the person who created the list and ask whether they changed its sharing. Microsoft's own wording for what happens is unambiguous: once the owner stops sharing, current list members no longer have access and the list becomes private again.
3. Ask them to open the list, select the sharing icon in the top-right corner of the list, select Create Invitation Link, then Copy Link, and send you the link again. Opening it puts the list back in your sidebar with every task still on it.
4. If they had selected Manage access and then Limit access to current members, your invitation link stopped working even though the list still exists. The new link from the previous step fixes that too.
5. If you own the list and are the one deciding, know what Stop Sharing does before selecting it: everyone else loses the list immediately, your own copy and all its tasks stay exactly as they are, and getting people back means sending a fresh invitation link rather than undoing anything.

4. Look for the Task in Outlook and in the Planner App in Teams

To Do, Outlook's task list, and the Planner app in Teams are three windows onto the same tasks stored in your mailbox.

1. Open Outlook and go to your tasks. All To Do tasks are stored on Exchange Online servers, which is why they show in both places automatically for the same account.
2. If the task is in Outlook but not in To Do, check what you set on it in Outlook. To Do does not display Outlook's start and end dates, task status, completion percentage, extra priority levels, work hours, colours, or categories. That information is stored safely — it is not shown in To Do, so a task defined mainly by those fields can look empty or missing.
3. Confirm the account: if Outlook has more than one account added, tasks appear against the account you set as the default mail account. A task added under a second account will not appear in a To Do app signed in to the first.
4. In Microsoft Teams, open Planner from the app bar down the left-hand side. Microsoft renamed this app — it was Tasks by Planner and To Do until April 2024 — so if your Teams still shows the old name, search the app bar for Tasks by Planner and To Do and open that instead.
5. Under My Tasks, check all three sub-views: Private Tasks, Assigned to me, and Flagged emails. A task assigned to you by a colleague lands under Assigned to me, and an email you flagged in Outlook lands under Flagged emails rather than in a list you created.
6. On Teams mobile, the Planner app shows only plans that have been added as a tab in a team channel. A task missing there is a limitation of the mobile app, not a sync failure — check on a computer before troubleshooting further.

Note: Which surface owns which kind of task is a recurring source of "where did it go" — Understanding Task Management in Microsoft 365 lays out what belongs in To Do, what belongs in Planner, and how the two feed each other.

5. Sign Out and Back In to Refresh an Expired Session

An app that stays signed in while its session has expired looks online and quietly stops exchanging data.

1. Before signing out anywhere, check that nothing is waiting to upload. Open To Do on the device you last typed into and confirm the tasks you added most recently are visible on a second device. Anything typed while that device had no connection exists only on that device until it uploads — read step 6 first if that describes you.
2. Signing out removes the local copy, not the tasks. Every task lives in your mailbox on Microsoft's servers, so they all download again when you sign back in.
3. On the web: open https://to-do.office.com, select your profile picture in the top-right corner of the page, and select Sign out. The page returns to the Microsoft sign-in screen.
4. In the Windows, Mac, or mobile app: select your name at the top of the left sidebar to open the account panel — the same panel you used in step 1 — and use the sign-out control there.
5. Close the app completely, then reopen it.
6. Sign in with your email address and password and complete any verification prompt your organisation asks for. Your lists rebuild as they download.
7. Check the list that was behind. It now matches the other device.

6. Clear What Is Blocking the Upload

Changes made on a device with no usable connection stay on that device, and a VPN or company firewall keeps them there.

1. Pick up the device holding the changes that never arrived, get it onto a connection you trust — a phone on mobile data rather than patchy office Wi-Fi — and leave To Do open for a minute. Held-back changes upload on their own once there is a window.
2. If you are on a VPN, disconnect it temporarily and reopen To Do. Microsoft lists VPN, proxy, and firewall configurations as causes of To Do sync problems. Turning the VPN off is reversible in one click and changes nothing about your account or your tasks — reconnect it as soon as you have tested, since other company systems need it.
3. If you see It looks like a firewall is preventing your data from syncing, or the web version returns a 503 error when you sign in, the problem is your network rather than your account or the app. Neither is something you can change from your own machine.
4. Send IT this, and paste in the exact message you saw: "Microsoft To Do will not sync on our network and reports a firewall error. Please confirm the To Do endpoints are allowed through the proxy and firewall — Microsoft lists them under its To Do troubleshooting guidance — and that outbound ports 443, 80 and 587 are open. My account is [your email address], the device is [laptop or phone], and the exact message is [paste it here]."
5. If instead the message reads Sync failed due to an issue with local storage on the app, the app's own local database on that one device is damaged. Microsoft's documented fix is to reinstall To Do on that device. Your tasks are safe on the server and download again after you sign in, so nothing is lost by reinstalling.

Verification: With the block cleared, add a task on the device that was stuck. It appears on your second device within seconds, and the tasks that had been held back arrive at the same time.

Troubleshooting

WARNING

Before you sign out, reinstall To Do, or let anyone reset the app on a device, confirm that everything you typed on that device has reached a second device. Tasks created while a phone or laptop had no connection are held locally until they upload, and a reinstall performed before they do discards them. When in doubt, get that device onto a working connection first and give it a minute — then reset.

Symptom / Error	Potential Cause	Solution
A task added on the phone never appears on the laptop	The two devices are signed in to different accounts	Select your name at the top of the sidebar on each device and compare the email addresses (Step 1). On Windows and Android, add the second account instead of switching.
A whole list disappeared from the sidebar	The list's owner stopped sharing it	Ask the owner to select the sharing icon on the list, then Create Invitation Link and Copy Link, and send you the link again (Step 3).
It looks like a firewall is preventing your data from syncing	VPN, proxy, or firewall blocking To Do	Disconnect the VPN and retest. If it persists, send IT the wording in Step 4 of section 6 with the exact message pasted in.
A 503 error when signing in to To Do on the web	Corporate network restriction	Try the same sign-in on a connection outside the office network to confirm, then raise it with IT using the same wording (Step 6).
Sync failed due to an issue with local storage on the app	The app's local database on that device is damaged	Reinstall To Do on that device. Tasks are held on Exchange Online servers and download again after sign-in (Step 6).
The task is in Outlook but not in To Do	The task uses fields To Do does not display	To Do does not show Outlook's status, percent complete, work hours, colours, or categories. Open the task in Outlook to see them (Step 4).
A completed task keeps un-completing itself	Two accounts, or two devices holding conflicting offline edits	Confirm both devices use one account (Step 1), then get the lagging device onto a working connection and let it upload (Step 6).
Tasks assigned by a colleague are nowhere in To Do	They arrive in a different view	Open Planner in Teams and check My Tasks > Assigned to me (Step 4).

Related Articles

• How to Use Microsoft To Do for Personal Task Management
• Understanding Task Management in Microsoft 365
• How to Fix OneNote Not Syncing

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