Why is my Mac running slow?

Look before you fix

Open Activity Monitor (Applications → Utilities) while the Mac is being slow, not afterwards. Each of its tabs answers one of the questions below, and the answer decides what to do. A fix chosen before looking is a guess, and most of the "speed up your Mac" advice online is a guess applied to every Mac at once.

1. Something is using the processor

On the CPU tab, sort by % CPU. One process near or above 100% for minutes at a time is the usual culprit: a stuck browser tab, a sync client catching up, a build or an export still running. Quit it, or close the tab, and see whether the Mac comes back. If it is a process you do not recognise, search its name before you force-quit it; some belong to macOS.

2. Memory pressure is high

On the Memory tab, look at the Memory Pressure graph at the bottom, not the free-memory figure. Green means the Mac has room. Yellow means it is compressing memory to cope. Red means it is moving memory out to disk (swap), and that is when everything starts to stutter.

The fix is to close what is holding the memory: usually a browser with many tabs, or two heavy apps open at once. A "free up RAM" button does not do this — it empties a cache macOS reads straight back — which is measured on does purging RAM help.

3. The disk is nearly full

macOS writes swap, caches and update files to the startup disk. When it is nearly full, all of that slows down or fails, and a Mac with a few gigabytes free often feels slow in ways that look like a memory problem. Check it in a terminal:

df -h /
sysctl vm.swapusage

If free space is in single figures of gigabytes, freeing space is the speed fix. Start with Mac storage full, which is ordered for exactly that. If most of the space is under System Data in Storage settings, what System Data isexplains which parts of it you can remove.

4. It is indexing after an update

After a macOS update, a migration or a big file copy, Spotlight re-indexes the disk and Photos re-analyses the library. You will see mds_stores, mdworker or photoanalysisd high on the CPU tab. It is temporary, and it finishes faster if the Mac is left awake and plugged in for an evening. If search stays broken for days afterwards, rebuilding the Spotlight index is the fix.

5. It is hot

A Mac that is hot slows its processor down to protect itself. A MacBook on a duvet, a fan clogged with dust or a sustained export on a laptop can all do it. This command reports whether macOS is limiting the processor right now:

pmset -g therm

And the slow start-up

If the Mac is slow mainly for the first few minutes after you log in, too many apps are opening at login. System Settings → General → Login Items & Extensions lists them, and the "Allow in the Background" list below shows the helpers that run without a window. Turn off what you do not need at startup.

What will not help

• Purging RAM. The free-memory number goes up; the Mac does not get faster.
• Clearing caches for speed. Caches make apps faster. Clear them for space, not speed — see how to clear the cache.
• Repairing permissions. macOS has done that itself since El Capitan.

If you have found the cause and want the fixes in order, see how to speed up a Mac.

Where the app comes in

RefreshYourMac shows the same three readings in its menu bar window: processor load with the busiest process named, memory pressure as macOS reports it, and the rate the Mac is swapping. Click the memory reading and you get the apps actually holding it, with a button to quit one. The menu bar icon turns orange as the disk fills and red when it is nearly full, so the third cause shows up before it becomes the slowdown.