iPhone Calendar contains duplicate and old entries after updating Mac to Ventura

After updated today to Ventura 13.4 on my M1 iMac, my calendar was totally screwed, seemingly similar to what you describe. I was afraid the crazy calendar would mess up my phone and other device calendars, so I switched

iCloud sync off for the calendar. Apple menu/system settings/Apple ID/iCloud/apps using iCloud/switch Calendar sync OFF. The duplicate entries on my Mac calendar were now gone, along with everything else except default holidays and such. But the calendar looked normal, if empty. So, I switched iCloud sync back on and the calendar repopulated my items in the normal fashion. It looks fine now. Whew!

I imagine you've checked to make sure iCloud is turned on for Calendar on all the devices and tried turning it off and back on a time or two on your Mac. Seems like I remember sync issues where it took more than one off/on to make it sync.

In my case, the Calendar was messed up after the last Ventura update (13.4). Apparently, something about that update or my iMac's interaction with it that messed up the Calendar's sync--something that did not happen when I did the sync again. Wonder if I had just left the screwed up Calendar alone, if it would have fixed itself the next time it did an automatic sync. Or would it have spread the disease to all the others? No idea.

I also have a MacBook that will need the update. I will shut off its Calendar iCloud button before I do it. You'd think if this were a common problem with that update, we'd be seeing lots of complaints about it, which I don't see.

I do the iCloud sync for calendar on all my devices. Interesting twist, this morning, I updated my iPad to IOS 16.5. Paranoid, I turned off the iPad's calendar sync before updating. After the update, guess what? iPad calendar totally screwed up, just like what I saw on my Mac. So, turning off the sync prior to updating was not the solution. But, this time, the fix was easy. I just turned the iCloud sync back on and the calendar went immediately back to its old normal self.

I also updated Ventura on my Macbook and IOS on my iPhone. No calendar problems with those.

Since I had this happen to two different devices with this recent round of updates, seems like a lot of people would have the same problem but I haven't seen that yet.

I'm very frustrated since updating to Ventura. I can't find a way to make my iPhone over ride my Macbook. Macbook keeps switching weekly and yearly events to daily. When it syncs it makes that happen on the phone. I have talked to Apple support numerous times. It has continued to happen with every new update. I only sync over usb for HIPAA privacy reasons.

I have already turned off all accounts - I don't use any other calendars so none of them need to sync to my iCalendar. In the edit menu, the start and end dates are the today's date (whatever day it is) but the repeat keeps getting switched from yearly or weekly to daily.

Is there a way to tell the sync menu to only sync from my phone to my Macbook and never vice versa?

My current ISO is 14.1.1 and iPhone is 17.1.2.

@prettybird

If you want the iPhone calendar to completely override the Mac's, would it work if you exported (for a backup in case something goes wrong) and then completely deleted the calendar on the Mac before doing the sync? You'd get a brand-new calendar with no chance of corrupting the iPhone's (at least the first time).

The whole point is to have a backup on my Mac. If the back up calendar is messed up, it doesn't serve the function. This is so frustrating. It's been going on for 2 years and it's still happening. This should be a very simple bug fix and it should have been fixed a long time ago. I'm much more interested in basic functionality than fancy new capabilities. If the basics don't work what's the point of a $4000 computer?

Well, the backup was for extra safety but if you don't trust it just skip that part and go straight for the erasure.

I cannot predict what will happen to the new calendar once it's transferred from the iPhone. Your situation seems pretty abnormal and I'm leaning towards a corruption of some sort that starting anew will eliminate. To make sure of it, don't just empty the old calendar, get rid of it completely.

Of course, there's also the good old method of deleting the preferences file that sometimes does wonders. You'll find com.apple.iCal.plist at ~/Library/Preferences.

Just to be sure, if you have repeating events each instance lasts only a few hours or one day maximum, right? Some people think that a weekly event starting January 1st and ending March 31st must have an end date of March 31st. No, the end date of the first instance is January 1st, but the end of repetition is March 31st. Otherwise, you're just creating a bunch of three-month-long overlapping events.

I finally decided to ask the question about duplicate entrees on my calendar on my Mac and should have done this months ago. So by doing just as you stated, going into ...Apple menu/system settings/Apple ID/iCloud/apps using iCloud/switch Calendar sync OFF and back ON it fixed the problem. Thanks for sharing.

That's a nice idea the first time around. The problem is that iCal in the Mac changes dates from weekly or yearly to daily. How do I make sure that doesn't happen again?