Tech Tip: Fixing Calendar Duplicates in MacOS Sierra

There’s an odd little problem with the macOS Calendar app that I’ve run into a number of times, both personally and during my years as a Mac consultant. Sometimes an event will be duplicated over and over, often filling a day on the calendar with copies of the same exact event. There’s a way to fix that problem once and for all…

Before we delve into the fix, let’s talk about some of the situations that seem to cause this issue. In my case, I use both iCloud-synced calendars and Google calendars. Some of these duplicates come from those Apple special calendars that you can subscribe to — U.S. Holidays, Birthdays, and Found in Mail. Most of the time, the duplicates will only appear in one or two calendars, and only on one device. For one of my clients a few years ago, the problem only happened on his MacBook Air, not on the iMac he had in his office nor on his iPhone.

One of the most frustrating things about this issue is that deleting those extra events never helped. They’d be gone for a few minutes, but would quickly start showing up again. I’d even try things like force-quitting Calendar and then restarting the Mac or deleting and then re-adding the calendar accounts, but none of those worked for long.

After digging through the Apple Support Communities for a while, I finally came upon a solution that worked. Here’s what you need to do:

1) Delete all calendar accounts from Calendar and macOS. Go to Calendar > Preferences > Accounts, click on each account in turn, and click the minus sign ( – ) to remove each calendar (see image below):

2) Quit the Calendar app (Command-Q or Calendar > Quit Calendar from the menu bar).

3) Open a terminal window, then delete all calendars and Calendar preferences. If you’re not comfortable with the terminal app, find a friend who has the necessary knowledge and ask them to do it for you.

4) Quit terminal.

5) Launch Calendar

6) Add your accounts back to Calendar. This is done by opening Preferences > Accounts, clicking the plus sign button, clicking on the calendar provider (iCloud, Exchange, Google, Facebook, Yahoo, Aol or other CalDAV account), then adding the appropriate account and password information.

7) Uncheck (hide) additional calendars from the Delegation tab. This ensures that only the primary calendar that you’ve added is viewable, not other calendars to which you may have been added (see image below):

8) Allow the download and sync of your cloud-stored calendar events to finish, and you’re done.

So what causes the duplicates? Google changed the way it supported CalDAV (Calendar Extensions to Distributed Authoring and Versioning) and multiple calendars a few years ago, and it’s thought that Calendar didn’t exactly work well with that new process. Through the various versions of Mac OS X and now macOS that have been released since that time, the issue still shows up on occasion.

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