Find the app that's hogging your Mac's CPU

Why it happens

An app can get stuck in a loop or keep working on something heavy, like a web page, a video export or a sync. It then uses the processor flat out, so your Mac gets warm and the fans speed up. Quitting or updating that one app usually brings everything back to normal.

How to fix it

1. Press Command-Space, type Activity Monitor and press Return. You can also find it in Applications, inside Utilities.

2. Click the CPU tab, then click the % CPU column heading so the busiest process is at the top. Click it again if the order is the wrong way round.

   Activity Monitor›CPU›% CPU

3. Watch the top few lines for a minute. Numbers over 100% are possible, because each processor core counts as 100%.

4. Switch to the app at the top and quit it with Command-Q, then open it again. In a web browser, the busy line is often one tab, so close tabs you don't need.

5. If the app won't quit, select it in Activity Monitor, click the stop button (an X) in the toolbar, then click Quit. Use Force Quit only if Quit doesn't work, as unsaved changes are lost.

Still not fixed?

1. Leave system processes alone. kernel_task is your Mac holding itself back to cool down, so close other busy apps instead. mds_stores, mdworker and photoanalysisd are indexing after an update or import and calm down on their own within a day or two.

2. Update the app. For App Store apps, open the App Store, click Updates and choose Update All.

   App Store›Updates›Update All

3. Restart your Mac to clear anything stuck in the background.

4. Help your Mac stay cool: use it on a hard, flat surface with the vents clear. On a laptop, Low Power Mode cuts heat and fan noise.

   Battery›Low Power Mode

5. If the fans stay loud with nothing busy in Activity Monitor, run Apple Diagnostics and contact Apple Support. A fan or temperature sensor may be faulty, which is a hardware repair.