Find the app that's slowing down your Mac with Activity Monitor

Why it happens

A Mac usually slows down because one app or web page is hogging the processor or memory. It might be stuck in a loop, busy with a big job, or simply badly behaved. Activity Monitor lists everything that's running, so you can spot the heavy one in seconds.

How to fix it

1. Press Command-Space, type Activity Monitor and press Return.

2. Click the CPU tab, then click the % CPU column heading so the busiest item is at the top.

   Activity Monitor›CPU

3. Then click the Memory tab and sort the same way. Something using several gigabytes is a likely cause.

4. When you find a normal app at the top, switch to it and quit it with Command-Q. If it won't respond, use Force Quit from the Apple menu.

   Apple menu›Force Quit…

5. Leave items you don't recognise, like kernel_task or WindowServer, alone. They are part of macOS and quitting them can log you out.

Still not fixed?

1. Restart your Mac. It clears out anything that has been running for days.

   Apple menu›Restart…

2. If the same app always tops the list, update it, or check the developer's website for a known problem.

3. Low on space? A nearly full disk slows everything down. Check General, then Storage.

   General›Storage

4. If the Mac stays slow with nothing busy in Activity Monitor, or the fans roar all the time, it could be hardware. Contact Apple Support or a repair shop.