How to Fix Microsoft 365 Calendar Events Not Syncing Across Your Desktop, Web, and Mobile Apps

Summary

This guide helps you troubleshoot and resolve: How to Fix Microsoft 365 Calendar Events Not Syncing Across Your Desktop, Web, and Mobile Apps. Follow the steps below to fix the issue.

Common Causes

When your Microsoft 365 calendar events fail to sync between Outlook desktop, Outlook on the web, and your mobile device, you risk missing appointments or double-booking meetings. This guide walks you through the most common causes and step-by-step fixes to restore consistent calendar synchronisation across all your devices.

Quick Fix Steps

1. Restart your computer and mobile device.
2. Check your internet connection on all affected devices.
3. Verify you are signed into the same Microsoft 365 account everywhere.
4. Force a manual sync in Outlook desktop by pressing F9.
5. Close and reopen the Outlook mobile app.

Detailed Instructions

Outlook Desktop (Windows)

1. Open Outlook and select File from the top menu.
2. Choose Account Settings, then select Account Settings again from the dropdown.
3. Click your Microsoft 365 email address, then select Change.
4. Ensure Use Cached Exchange Mode is checked.
5. Drag the Mail to keep offline slider to All.
6. Select Next, then Finish, and restart Outlook.
7. Press F9 to manually send/receive and force a calendar sync.

Outlook on the Web

1. Open your browser and go to outlook.office.com.
2. Sign in with your Microsoft 365 credentials.
3. Select the Calendar icon from the left navigation pane.
4. Refresh the browser page to ensure you are viewing the most current server data.
5. If events are missing here but present on desktop, the issue is likely with your desktop Outlook sync, not the Microsoft 365 server.

Outlook Mobile (iOS and Android)

1. Open the Outlook app on your phone or tablet.
2. Tap your profile icon or initials in the top-left corner.
3. Select the Settings gear icon.
4. Tap your email account under Mail Accounts.
5. Toggle Sync Calendars off, wait ten seconds, then toggle it back on.
6. If the issue continues, remove the account from the app and add it again using your full Microsoft 365 email address and password.

Apple Calendar on macOS or iOS

1. Open Settings (iOS) or System Settings (macOS).
2. Navigate to Passwords or Internet Accounts.
3. Select your Microsoft 365 account.
4. Ensure the Calendars toggle is switched on.
5. On iOS, pull down on the Calendar app screen to manually refresh.

Troubleshooting

Check for Duplicate Calendars

If you have added your Microsoft 365 account more than once, events may appear in one calendar but not sync to others. In Outlook desktop, go to File > Account Settings > Account Settings and review the Email tab for duplicate entries. Remove any duplicates and keep only your primary Microsoft 365 account.

Verify Calendar Permissions

If you are viewing a shared calendar that is not updating, confirm you still have permission to access it. In Outlook on the web, right-click the shared calendar in the left pane and select Sharing and permissions. Ensure your access level is set correctly.

Clear Outlook Cached Data

Outlook desktop stores a local copy of your mailbox. If this cache becomes corrupted, calendar events may fail to sync.

1. Close Outlook completely.
2. Press Windows Key + R to open the Run dialog.
3. Type %localappdata%\Microsoft\Outlook and press Enter.
4. Locate the .ost file for your email profile and rename it to .old.
5. Restart Outlook. It will rebuild the cache and resynchronise your calendar from the server.

Renaming the .ost file forces Outlook to download your mailbox again. Depending on your mailbox size and internet speed, this may take some time. Do not delete the file; simply rename it.

Check Mobile Device Sync Settings

On Android, battery optimisation can prevent the Outlook app from syncing in the background. Go to Settings > Apps > Outlook > Battery and select Unrestricted. On iOS, ensure Background App Refresh is enabled for Outlook under Settings > General > Background App Refresh.

If calendar events appear correctly in Outlook on the web but not on your desktop or mobile device, the Microsoft 365 server is working normally. Focus your troubleshooting on the specific app or device where events are missing.

If you have completed all steps above and your calendar events still do not sync across devices, Open a Ticket with our support team for further assistance.

Still Having Issues?