Calendar very slow with macOS Monterey

I use Apple Calendar exclusively (except when I have to create a meeting invite with others at work). But, I accept invites and such on my Apple Calendar. I have a number of iCloud calendars I sync with on three Macs and two iOS devices. All of these also sync with a work Exchange calendar.

I have been seeing this delayed event rendering on the iOS devices for a while as I'm on the iOS beta program. It was annoying but I made reports. The symptom was that I'd go to a day in the calendar but events would not be there but would fill in in a few seconds.

When I upgraded my Mac to Monterey, I started seeing the same annoying behavior on the Mac's Calendar app.

I unsubscribed to the Exchange calendar on the Mac. Lo and behold, the Calendar app was working like it was its old self. I tried unsubscribing on the iOS devices and, they too, started functioning nicely again. Just turning off the Exchange calendar in the Calendar app didn't do anything. I had to "unsubscribe" from the Exchange calendar.

Earlier in another thread, I through it was a client-side issue. I still believe that. But now, I am betting it is an Exchange client-side, either Apple's implementation or Microsoft's implementation.

Have you installed or run any "cleaning", "optimizing", "speed-up", anti-virus or VPN apps on your Mac?

Boot into Safe Mode according to Start up your Mac in safe mode - Apple Support and test to see if the problem persists. Reboot normally and test again.

NOTE: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

Correction: on MacOS, if I turned off the Exchange Calendar in the Calendar app calendars window, things worked well again.

The problem still occurs in safe mode for me. Slow syncing, spinning wheels and delays when moving between weeks. If I uncheck the Exchange Calendar the problem goes away. If I check it again the problem comes back.

The problem is with Exchange, not Clalendar or Monterey.

This is from one of the posts in this topic:

"I unsubscribed to the Exchange calendar on the Mac. Lo and behold, the Calendar app was working like it was its old self. I tried unsubscribing on the iOS devices and, they too, started functioning nicely again. Just turning off the Exchange calendar in the Calendar app didn't do anything. I had to "unsubscribe" from the Exchange calendar."

I have the same exact issue. Calendar app very slow almost useless on the Mac and same on iPhone. Looks to be associated with MS Exchange. If I turn off (uncheck) the Exchange Calendar in the Calendar app calendars window, things worked well again.

I see the same behavior as Armando Stettner (Hi Armando, from days of yore!). If I merely hide the Exchange Calendar, things speed up drastically and the spinning ball of death goes away. To me, it is clearly a client-side issue and a regression, since I did not see this behavior in earlier versions of MacOS.

Same issue here, as soon as I updated to Monterey. Spinning wheel of death every time I open Calendar or switch weeks. Turn off the Exchange calendar and it goes away. Same with iPhone Calendar app. Google calendars show up right away, but the Exchange calendar takes 5-6 seconds. Hope they fix this soon!

Same problem, Exchange sync is the issue. It takes anywhere between 5 to 15 seconds to switch from one week to the other.

Problem disappears when I disable my Exchange calendar and reappears when I enable it again.

Same issue as well since I upgraded my iPhone to IOS 15 so obviously Apple brought the same problematic Exchange sync framework in both MacOS Monterey and IOS 15.

I use Apple's Calendar app for my iCloud, Personal Google and work G-Suite accounts. Had no issues until I upgrading to macOS Monterey. Now the Calendar app hesitates all the time and runs *very* slow. I have tested this on two different MBPs (both Pro 2019 and 2020 models) with the same result.

The delayed rendering goes away as soon as I disable my G-Suite calendar in the app on both my MBPs.

Apple, this is impacting productivity for myself and lots of other Corporate users. Please add this to your BUG list and advise when it will be resolved.

I am having the same issue. I am running MacOS Monterey on a MB Pro 2.3GHz Intel Core i9 / 16gb ram. I use Apple Calendar to sync with my iCloud account, two gmail accounts, and two Exchange accounts. When I turn off the calendar for the Exchange accounts the problem goes away. It used to refresh instantaneously before I upgraded to Monterey.

So the problem is clearly that Monterey broke Apple Calendar's ability to sync with Exchange email accounts quickly. I hope they fix this glitch soon because it's a super annoying drag on productivity.

Solved with MacOS 12.1. At Last!

As stated by others already, the update with12.1solved the issue for me as well.

12.1 patch worked for Mac and latest iOS upgrade worked too. It was a torturous month, and I relearned the wisdom of waiting to do a major Mac OS release install.

Same here, I have carried out a clean install of Monterey on a 16" MacBook Pro. Everything works well except for the slow Calendar issue. I have an exchange account for work and see slow syncing, spinning wheels and delays when moving between weeks. If I uncheck the Exchange Calendar the problem goes away. I will also have to move away from using Calendar app because of this unfortunately.