My phone and laptop aren't syncing (Microsoft To Do)

Try this in order:

1. Confirm the same account is signed in on both devices Microsoft To Do syncs tasks and lists when the same account is used on each device. Tasks are stored on Exchange Online and should sync automatically.
2. Update Microsoft To Do on both phone and laptop Older app versions can break cross-device syncing. Microsoft states the best experience requires the latest version, and older versions can stop syncing across devices.
3. Do not sign out if there may be unsynced tasks on the laptop If the laptop has local unsynced changes, signing out can cause those unsynced items to be lost.
4. Check whether the tasks appear in the web app Open Microsoft To Do on the web and verify whether the missing tasks appear there.
   • If the tasks appear on the web and on the phone, the issue is likely the laptop app.
   • If they do not appear on the web either, the issue is likely account or sync related rather than just the laptop.
5. Reinstall the laptop app if the issue is only on that device If the phone shows the tasks but the laptop app does not, reinstalling the desktop app can refresh local app state.
6. If a VPN, proxy, or firewall is in use, disable it temporarily or have the required endpoints allowlisted Microsoft notes that VPNs, proxies, and firewalls can prevent To Do from syncing. If this is on a managed network, the IT admin should allowlist the required Microsoft endpoints and ensure ports 443, 80, and 587 are open.
7. If syncing is stuck on all devices, contact Microsoft Support When the issue affects desktop, mobile, and web, that points away from a single-device problem.

A practical way to narrow it down is:

• Phone shows tasks + web shows tasks + laptop does not → update or reinstall the laptop app.
• Phone shows tasks + web does not → likely a sync/account issue.
• All devices fail → likely broader sync or network issue.

References:

• Syncing your Microsoft To Do account
• Important updates are available for Microsoft To Do apps
• Why do I receive the message “We're having trouble syncing your data” ?
• Error messages in Microsoft To Do
• Microsoft To Do sync completely stuck on all devices (iPhone & Windows) - Microsoft Q&A
• My tasks that I entered into the To Do app dissapeared - Microsoft Q&A