High CPU and battery drain in Sierra for CalendarAgent, and CalNCService

I found a solution that worked for me!

Via: https://robert.accettura.com/blog/2012/08/19/how-to-stop-calendaragent-from-eati ng-cpu/

CalendarAgent is essentially Calendar’s backend (that’s how it’s also able to power the notification center). The best resolution I’ve found is to completely clear out the calendar and recreate it. Process I used was as follows:

1. Remove the Calendar from “Mail, Contacts & Calendars” pref panel (just uncheck from the account). Then go into Calendar and make sure the account is removed. If it’s not, remove it.
2. Delete ~/Library/Calendars/
3. Delete ~/Library/Preferences/com.apple.iCal.plist
4. Go back into the “Mail, Contacts & Calendars” pref panel, put the calendar back. Give it some time to download.

I have the same thing happening on my iMac (27-inch, Late 2012)

Sierra: 10.12.2

I read a post mentioning issues with the stock Reminders app, so I removed all reminders and other lists. This took CalendarAgent and CalNCService from 50% and 40% to 20% and 15% respectively.

I have tried all solutions listed here(clearing cache, removing/adding accounts, removing/adding one account service component at a time) and other threads but no matter what I do, CalNCService keeps returning to >100% usage.

This problem happens continuously back to 2012.

How is that possible that it is STILL not fixed? Even after thousands of user's reports?

I was tired of "svchost.exe" eating 100% CPU on Windows, switched to macOS and now story goes again. Where is famous Apple quality?

Developer of CalNCService should be fired immediately.

Thank you so much. I had this problem and tried your temporary fix of unchecking the contacts in my google account and it worked. I don't know why, but this makes a huge difference to my CPU loading.

Best wishes,

I'm using a MBP mid-2015 with MacOs Sierra 10.12.5. I was scratching my head trying to find solutions and finally found it.

Issue: CalNCService is running high on CPU around 100%. Temperature rises and fan speed increases. Temperature from 48ºC-61ºC

I've tried removing google and iCloud calender, contacts and all. But the problem came back. I did a check one by one by deselecting contacts, then later reminders and so on while checking activity monitor. Found that "Reminders" was the culprit.

Solution: Delete everything from Reminders, and type it out again. CalNCService drops right away after removing list of reminders. I haven't tried exporting and re-importing. Temperature after fix is around 39ºC-42ºC

Problem solved for me.

All the best and thank you!

I wonder how many new macs were sold because of the high CPU utilization from this problem?

I disabled all the mail, contact, and calendar sync from the system preferences/internet accounts list of accounts... and it seems better, but its only been 30 min so far

So go ahead and use your fancy mac, just don't expect it to sync with any internet accounts - LOL

Thanks for this thread - very useful!

I've tried various combos of the suggestions on this thread, but the one that works for me (I use google calendar, and sync everything to that) is to just disable the calendar sync for google. Hey presto bingo, cpu back to normal. You can see that happen immediately you check / uncheck the tick box so it's definitely the cause for me.

Can't believe apple have let this run for so long, but there you go... Hopefully my MBP battery will start behaving now!

I found suitable for me solution, that stabilizes CPU usage from CalNCService to normal (practically near zero %).

First, I disable all notifications for Reminders - without any effect.

Then I deselect Reminders in my iCloud account (Settings-Internet accounts-iCloud-Reminders) and CalNCService immediately drop to 0%, so I became sure that the problem is with my Reminders app or content.

I check my Reminders content and found that I have more than 2000 already completed to-do's in different folders, so I made the backup (export all tasks to disk) and delete all completed tasks in each folder.

After that re-enable all notifications for Reminders.

As an additional step, I disable Reminders on my iPhone, delete them from the phone and then re-enable - to be sure I have no old completed tasks on the phone.

After about half-hour (I think, re-syncing with iCloud) CPU usage for CalNCService became 0% and stay stable near zero for last 3 hours. I hope, forever 🙂

May be this will help you as well.

(MBP mid-2017, macOS Sierra)

My solution was to turn off the calendar for a (work-related) CalDAV account—a Zimbra email account. The calendaragent CPU use immediately dropped from 200% to negligible. Turning off other Calendar accounts, including iCloud, had no effect.

Correction: while this solution did work, once I opened reminders or calendar app, it came right back.

I'm out of ideas.

Exactly same issue here.

I'm having one iCloud and an Exchange account.

Same here - really disappointing!