How the sync actually works.
Three connections, one direction. Outlook stays untouched as the source of truth; Google Calendar receives auto-updating copies of your meetings typically within about a minute of Outlook's change notification.
1. Read: a change feed from your Outlook calendar
When you connect Outlook, the app registers a Microsoft Graph subscription on your calendar — Microsoft’s official mechanism for change notifications. From then on, Microsoft pushes a notification the moment an event is created, updated, moved, or deleted. The Microsoft side is read-oriented: Calendar Syncer never creates, edits, or deletes anything in Outlook.
2. Write: shadow events in an app-created Google calendar
Each Outlook event gets a corresponding “shadow” event in Google Calendar, created through Google’s Calendar API. By default these land in a separate calendar the app creates — your primary Google calendar stays untouched, the Google permission surface stays narrow, and you can toggle the synced calendar’s visibility (or delete it) at any time. Mappings between each Outlook event and its shadow copy ensure a reschedule updates the right event and a cancellation removes it.
3. Repeat: notifications plus an hourly safety net
Change notifications make sync fast — typically within about a minute of Outlook's change notification. Because no notification system is perfect, an hourly reconciliation sweep catches anything a notification misses, and subscriptions are renewed automatically before they expire. The result is a Google calendar you can trust to be current without ever thinking about it.
What this design deliberately avoids
- No write-back: one-way only — see why that is the safer default for work calendars.
- No published links: no anonymous ICS URLs floating around, and no 12–24 hour refresh lottery.
- No desktop dependency: nothing to install, no PC that must stay on, and immune to the classic-Outlook add-in retirement.
- No plaintext secrets: OAuth tokens and cached event data are encrypted at rest — the full inventory of what is stored and why is on the security page.
Frequently asked questions
How fast do Outlook changes appear in Google Calendar?
Typically within about a minute. Microsoft sends a change notification the moment an event is created, moved, or cancelled, and the sync runs immediately on receipt. An hourly reconciliation sweep additionally catches anything a notification ever misses.
Does the sync ever write to my Outlook calendar?
No, never. The Microsoft side is read-oriented by design: the app reads events and receives change notifications. All writes go to Google Calendar — and by default into a dedicated app-created calendar, not your primary one.
Do I need to keep a computer running?
No. Everything runs server-side between Microsoft's and Google's clouds. Your devices are not involved in the sync path at all.
What happens when I disconnect?
Syncing stops immediately and you can revoke the app's access in your Microsoft and Google account settings. The app-created Google calendar with the synced copies is yours to keep or delete in one click, and stored sync data can be removed from Settings.
Which calendars can I connect?
Up to three Outlook calendars — personal outlook.com accounts and Microsoft 365 work or school accounts — synced into one Google account. Each connection can be managed separately.