If you sync two calendars both ways with two Zaps (Google → Outlook and Outlook → Google), every event slowly multiplies. Here's why, and how to fix it with built-in Zapier tools.
Why it loops.
Zap A copies a new Google event to Outlook. To Outlook that copy is a brand-new event, so Zap B copies it back to Google, where it's new again. Updates make it worse: the "event updated" trigger can't tell which copy an event belongs to, so it creates another one.
The fix has two parts.
- Mark every copy. When a Zap creates the copy, add a short marker at the end of the description. Then put a Filter by Zapier step right after each trigger: only continue if the description does not contain the marker. That alone stops the ping-pong.
- Remember which event is a copy of which. Store the pair (source event ID → copy's event ID) when you create the copy, in Storage by Zapier or a Zapier Table. In the "updated" Zaps, look up the source ID first and update that copy instead of creating a new one.
Two things that still catch people out.
- Recurring events: depending on the trigger, a series arrives as one event or as every occurrence. Check which before turning the Zap on, or a weekly meeting becomes dozens of events.
- The first run: test on a scratch calendar first, so a mistake doesn't copy your whole calendar.
Happy to help if you're stuck; post your Zap steps (without account details) and tag me.
