In plain words
A slow Mac is like a cluttered kitchen: too many pans on the hob (open apps), a worktop covered in boxes (a full disk), and guests all arriving at once when the door opens (login items). You tidy up before blaming the oven, and you certainly do not call a "miracle product" salesman.
A sluggish Mac almost always has an identifiable cause: a greedy app, a disk that is too full or too many items at startup. Go through these checks in order.
1. Restart, properly
Many Macs are never shut down, only put to sleep. A full restart (Apple menu → Restart) frees memory and ends stuck processes. It is also a chance to install pending updates.
2. Spot the app that is using resources
Open Activity Monitor (⌘ + Space, type "activity").
| Tab | What to look at |
|---|---|
| CPU | Sort the "% CPU" column: an app constantly at 100% slows everything down |
| Memory | The Memory Pressure graph at the bottom: green, all is well; yellow or red, memory is short |
| Energy | Apps that drain a laptop's battery |
To stop a stuck process, select it and click the ✕ button at the top of the window.
Tip
The most common culprit is the web browser with dozens of open tabs. Each tab uses memory: close the ones you do not need.
3. Free up disk space
Apple menu → System Settings → General → Storage. To be safe, keep at least 15% free space: macOS needs room for its virtual memory, updates and snapshots.
The recommendations shown let you:
- store files in iCloud and keep only recent ones locally;
- empty the Trash automatically after 30 days;
- spot large files and unused apps.
4. Lighten startup
Apple menu → System Settings → General → Login Items & Extensions ("Login Items" on older versions). Remove from the Open at Login list whatever does not need to start with the Mac, and turn off Allow in the Background for unknown or useless apps.
5. Update macOS and your apps
Apple menu → System Settings → General → Software Update, then the App Store for apps. After a big update, the Mac can be slow for a day or two while it re-indexes its files: that is normal.
6. Test in safe mode
Safe mode starts macOS with the bare minimum. If the Mac is fast there, the problem comes from software launched at startup.
On an Apple silicon Mac: shut it down, hold the power button until the startup options appear, select the disk, hold ⇧ and click Continue in Safe Mode. On the login screen, "Safe Boot" confirms the mode.
What not to do
Warning
Avoid apps that promise to "clean" or "speed up" your Mac. At best they do nothing, at worst they slow the system down, show fake alerts to make you pay, or delete useful files. The built-in tools are enough.
If nothing helps and the Mac is several years old, the memory or the disk may be to blame. The built-in hardware test (Apple Diagnostics) checks the components: on an Apple silicon Mac, hold the power button at startup, then press ⌘ + D on the options screen.