Google Calendar and Outlook Sync Not Working? Here Are the Fixes

When Calendar Sync Breaks, Everything Breaks

Few things are more stressful than discovering your calendars are out of sync, especially when you find out because you just double-booked yourself. Whether you are using a manual ICS subscription, a sync tool, or a custom integration, things can and do break.

This guide covers the most common sync issues between Google Calendar and Outlook, along with step-by-step fixes for each one.

Issue 1: ICS Subscription Stopped Updating

If you are using the free ICS subscription method to view Google Calendar events in Outlook (or vice versa), the most common problem is stale data.

Symptoms

• Events from days ago are missing
• Changes you made are not reflected
• New events do not appear

Fixes

• Check the ICS URL: Go back to Google Calendar settings and verify the URL has not changed. Google occasionally regenerates these URLs for security reasons.
• Remove and re-add the subscription: In Outlook, delete the subscribed calendar and add it again with a fresh URL.
• Wait it out: Outlook can take up to 24 hours to refresh ICS subscriptions. There is no way to force an immediate update through the web interface.
• Consider switching methods: If the slow refresh rate is causing problems, ICS subscriptions may not be sufficient for your needs.

Issue 2: OAuth Token Expired

If you are using a sync tool that connects via OAuth (the "Sign in with Google/Microsoft" flow), your connection can expire or be revoked.

Symptoms

• Your sync tool shows an error about authentication or permissions
• Sync stopped working on a specific date
• You recently changed your password or enabled two-factor authentication

Fixes

• Re-authenticate: Go to your sync tool and reconnect the affected account. This refreshes the OAuth token.
• Check your Google security settings: Visit myaccount.google.com and look under "Third-party apps with account access." Make sure your sync tool is still authorized.
• Check your Microsoft account: Similarly, visit account.microsoft.com and review app permissions.
• Review recent security changes: If you recently changed your password, enabled MFA, or your organization changed its security policies, you will need to re-authorize any connected apps.

Issue 3: Events Appearing at Wrong Times

Time zone issues are surprisingly common, especially for people who travel or work across time zones.

Symptoms

• Events show up an hour (or more) off from the correct time
• All-day events span two days instead of one
• Recurring events are inconsistent

Fixes

• Check time zone settings in both calendars: Make sure Google Calendar and Outlook are set to the same time zone, or at least the correct ones for each account.
• Check your device time zone: Your computer or phone might be set to a different time zone than your calendar accounts.
• Look at the event details: Some calendar clients create events in the device's local time zone rather than your calendar's default. Open the problematic event and check its time zone setting.
• For all-day events: These are handled differently across platforms. Some sync tools treat them as "floating" times without a time zone. If your tool supports it, configure how all-day events should be handled.

Issue 4: Duplicate Events Everywhere

Duplicates are one of the most frustrating sync issues. Instead of one clean copy of each event, you end up with two, three, or even more copies.

Symptoms

• Every event appears twice (or more) on one or both calendars
• Deleting a duplicate causes it to reappear
• The problem gets worse over time

Fixes

• Check for multiple sync methods running simultaneously: This is the most common cause. If you have both an ICS subscription and a sync tool pointing at the same calendar pair, you will get duplicates. Disable one method.
• Check for sync loops: If you sync A to B and also B to A through different tools, you can create an infinite loop of duplicates. Use a single tool that handles bidirectional sync properly.
• Clean up existing duplicates: Most calendar apps let you bulk-delete events. Remove the duplicates, then fix your sync setup before re-enabling.

Issue 5: Recurring Events Not Syncing Correctly

Recurring events are the hardest type to sync because Google and Microsoft handle them differently under the hood.

Symptoms

• Only the first instance of a recurring event syncs
• Exceptions (modified instances) do not propagate
• Deleting one instance deletes all instances on the other calendar

Fixes

• Check your sync tool's documentation: Not all tools handle recurring events the same way. Some sync each instance individually, while others sync the recurrence pattern.
• Update your sync tool: Recurring event handling has improved significantly in 2025 and 2026. Make sure you are on the latest version.
• Test with a new recurring event: Create a fresh recurring event to see if the issue is with legacy data or ongoing sync.

Issue 6: Sync Tool Is Working but Events Are Delayed

If events eventually sync but take too long, the issue is usually with how your tool detects changes.

Symptoms

• Events appear on the target calendar, but 15 to 30 minutes late (or longer)
• Some events sync fast while others are slow

Fixes

• Check your tool's sync interval: Some tools poll for changes on a schedule (every 5 minutes, 15 minutes, etc.). A shorter interval means faster sync but may cost more.
• Look for webhook support: The fastest sync tools use webhooks or push notifications from the calendar API, which means changes are detected instantly. CalendarSync uses this approach for near-instant sync.
• Check your plan tier: Many sync tools offer faster sync on higher-tier plans.

When to Start Fresh

Sometimes the cleanest fix is to start over. If you are dealing with hundreds of duplicate events, broken recurring series, or a mess of overlapping sync tools, consider:

1. Disabling all existing sync methods
2. Cleaning up duplicates and broken events on each calendar
3. Setting up a single, reliable sync tool from scratch
4. Testing thoroughly before trusting it for real meetings

If you are looking for a fresh start, CalendarSync's free tier lets you test with one calendar pair before committing.

Preventing Future Issues

• Use only one sync method per calendar pair
• Monitor your sync tool's status page or dashboard regularly
• Keep your OAuth connections current by re-authenticating when prompted
• Test your sync setup after any security changes (password updates, MFA changes, etc.)