remindd sometimes spikes over 100-200% CPU usage Over the past few months, I have experienced my MacBook turning on its fans because of high CPU usage. When that happens, I see that a process called remindd is using 100-300% CPU for a long time, usually more than 10 minutes. It seems this process belongs to the reminders app, which I do use, but it doesn't make any sense that the app has such a high CPU usage. This is not a one time thing, it happened at least 5 times in the last few weeks. I usually ended up killing the process or restarting my Mac. Quitting the reminders app does not stop the process.

What can I do to prevent this?



It may be related to the reminders app constantly syncing:



Although that opens only more questions than it answers.

I'm using the latest MacBook Pro 16" with MacOS 10.15.4 (19E287)
What worked for me is to turn off Reminders syncing, reboot, then turn it back on. Assuming you are running Catalina, you would go to:
System Preferences -&gt; Internet Accounts -&gt; iCloud -&gt; Uncheck Reminders
It took a bit for my reminders to sync again, but after that, there were no more issues with Reminders app lockup and the remindd run away CPU usage.
However, as of recent (Catalina 10.15.7), remindd has run away CPU usage regardless if I turn off/on syncing or I just leave it off the all the time.
Since I posted this answer, I will add that even with Big Sur (including 11.3 update), so long as I have Reminders enabled, I get high CPU usage with remindd. In addition, reminders are not properly syncing between my iPhone, iPad, and Mac. It appears there is some corruption in my Reminder data and it is not getting fixed with macOS updates.