Why is my Mac suddenly slow?

What just started?

The app that started the slowdown is usually at the top of Activity Monitor’s CPU list.

1. Open Activity Monitor. It’s in Applications > Utilities, or search for it with Spotlight.
2. Click CPU, then click the % CPU column heading to sort the list, busiest first.
3. Look for an app that stays at the top. Apps jump up for a moment when they open or save, which is normal; an app that stays there for minutes is doing sustained work.

Activity Monitor counts each processor core as 100%, so an app working on several cores can show more than 100%, as Blender does here. If you aren’t sure what an app is doing, switch to it: an export or render usually shows its progress.

Is memory running short?

A sudden slowdown can also come from memory, when one app grows until macOS runs short.

1. In Activity Monitor, click Memory.
2. Look at the Memory Pressure graph at the bottom. Green means your Mac is using its memory efficiently. Yellow or red means it’s short of memory.
3. If it’s yellow or red, sort by Memory and quit the apps you don’t need, saving your work first.

Did something start in the background?

Some work runs without a window. After you move your data to a new Mac, for example, Spotlight indexes it, and Apple notes that the fans speed up while it does. This kind of work finishes on its own; Activity Monitor’s CPU list shows it while it runs.

Apps that open at login can start work in the background too. To see them, choose Apple menu > System Settings, click General, then click Login Items & Extensions.

What should I do about it?

• If the work is something you asked for, such as a render, an export or a large download, let it finish or pause it in the app.
• If you don’t need the app right now, quit it from its own menu. Save your work first.
• If it isn’t responding, select it in Activity Monitor, click the Stop button at the top of the window, then choose Quit. Use Force Quit only if Quit doesn’t work, because unsaved work in that app is lost.
• If no app stands out, check the other usual causes, a nearly full startup disk or a hot Mac: Why is my Mac slow? walks through each.

Questions people also ask

Is a sudden slowdown a sign my Mac is failing?

Usually not. A sudden slowdown most often has a busy app or background work behind it, which Activity Monitor shows. If no app stands out, Apple suggests checking the disk with Disk Utility.

Why is kernel_task using so much CPU?

kernel_task is part of macOS. Apple says one of its jobs is to keep the processor from getting too hot, by making it less available to processes using it heavily. Find the app working hard, and give your Mac room for air.

Why is my Mac slow only some of the time?

Often because an app works in bursts, such as syncing, backing up or exporting. Watch Activity Monitor’s CPU list when it happens, to see which app is at the top.