Why Is My Mac So Slow? A Step-by-Step Diagnosis

A slow Mac usually comes down to one of four things: not enough memory, a runaway app loading the CPU, a nearly full disk or heat. Check them in that order in Activity Monitor and Storage settings — you don’t need a cleaner app for any of it.

“Slow” is a symptom, not a diagnosis: the spinning cursor, windows that lag, a fan that won’t quiet down. When a MacBook is running slow, a list of twenty tips won’t help. What helps is checking things in order.

First find what is overloaded, then find who is to blame.

Everything else is detail.

First, pin down what is slow

Answer three questions before you open anything:

• is everything slow, or just one app;
• has it always been like this, or did it start at some point — after an update, after sleep, after plugging in an external display;
• is it slow while you work, or even when the Mac is sitting idle.

Each answer narrows the search. If only the browser crawls, the problem is most likely the browser, not the Mac. If it started right after a macOS update, Spotlight may be re-indexing your disk, which Apple says can take hours or even days. What’s normal after an update and when to stop waiting is covered in Mac slow after an update.

For the rest you’ll need Activity Monitor: Applications → Utilities → Activity Monitor, or just type its name into Spotlight. Along the top are the CPU, Memory, Energy, Disk and Network tabs.

Step 1. Memory

Open the Memory tab and ignore Memory Used. Look at the Memory Pressure graph at the bottom instead. “15 of 16 GB used” says almost nothing: macOS deliberately fills spare memory with cache.

Apple’s guide reads the colors like this: green means memory is being used efficiently, yellow means the Mac might eventually need more, red means it needs more. Green — memory isn’t your problem, move on.

While you’re there, glance at Compressed and Swap Used. When memory runs short, macOS first compresses data it hasn’t needed lately right in RAM, then moves it out to disk — that’s swap. A little swap with a green graph is normal; how much is normal and when it’s a problem is in the swap guide. Yellow or red graph — see the guide on memory pressure.

Step 2. CPU

Switch to the CPU tab and click the % CPU column header so the hungriest processes rise to the top. One app sitting near 100% while you aren’t even using it? That’s your culprit: save your work and restart it.

System processes near the top are not malware:

• kernel_task is the kernel. Apple explains that it helps manage CPU temperature by making the CPU less available to whatever is using it hardest. A busy kernel_task is a result of heat, not the cause (more in the kernel_task guide);
• WindowServer draws everything on screen. It grows with the number of windows, displays and animations; how to find what exactly loads it is in the WindowServer guide;
• mds_stores and mds are Spotlight indexing. After an update or a migration they can run for a long time, then settle down. Indexing is fastest when the Mac is on power and not in use: leave it overnight and keep it from sleeping.

Step 3. Disk

Check your free space: System Settings → General → Storage. When the disk is nearly full, macOS has little room for swap, caches and downloaded updates, and everything slows down.

You don’t need a cleaner. Space usually goes to old downloads, iPhone backups, photo and video caches and forgotten virtual machines. Storage shows recommendations and a breakdown by category — start with the biggest items. If System Data takes the most, work through the System Data guide.

Step 4. Heat

If the Mac is hot and slow specifically under load — exporting video, building a project — the system is slowing itself down to stay cool. That’s normal behavior, not a fault. It’s most noticeable on a MacBook Air with Apple silicon: there’s no fan, so under long, heavy load slowing down is its only way to shed heat.

Check the basics: the Mac is on a hard surface rather than a bed or a pillow, the vents are clear, and the room is no warmer than 35 °C (95 °F), as Apple recommends for laptops. In Terminal, pmset -g therm shows whether the system has logged any thermal warnings; if it hasn’t, it says so. Where to get degrees and when heat is a reason to worry is covered in the Mac temperature guide, and why the fan is loud — in the fan noise guide.

If your MacBook is also draining fast, where to see battery usage and what eats the charge is in MacBook battery drain; whether the battery itself is worn is in MacBook battery health.

Step 5. If everything looks fine

1. Restart the Mac. It’s boring, but it clears stuck processes and memory leaks.
2. Review login items: System Settings → General → Login Items & Extensions. Remove what doesn’t need to start every time.
3. Start up in safe mode, which keeps some third-party software from loading at startup. On a Mac with Apple silicon, shut it down, press and hold the power button until startup options appear, select your disk, then hold Shift and click Continue in Safe Mode. On an Intel Mac, hold Shift right after turning it on until the login window. If it’s faster in safe mode, look for the culprit among extensions and login items.
4. Disable browser extensions one at a time if it’s the browser that drags.

If the Mac is still slow in safe mode and in a fresh user account, it’s time for a repair shop: the problem may be hardware.

Cheat sheet

What not to do

Don’t install “boosters” or memory cleaners: the memory they free fills right back up with cache, and apps have to reload from disk what was sitting there. Don’t delete system files on a hunch. And don’t start with an NVRAM or SMC reset: on Apple silicon, Apple says the NVRAM reset steps aren’t needed, and the SMC resets itself on restart.

In the app

Mac Resources works as an always-on first glance. Its menu bar item shows whichever of CPU, memory or GPU is busiest, updates every two seconds and turns red above 80%. Its menu lists the current numbers: CPU, Memory, Disk used, GPU and Battery. The large Last Hour widget shows every graph for the past hour, so you can see when the load started. Widgets refresh once a minute — macOS doesn’t allow more often. To add one, see the guide to desktop widgets.

The app doesn’t show processes, temperature or fans: the sandbox doesn’t allow it. Look for the culprit in Activity Monitor, and for temperatures use Stats or iStat Menus — they’re compared in the guide to menu bar system monitors.

Next step: get to know the tool itself with Activity Monitor tab by tab. And if you suspect you simply don’t have enough memory, read whether 8 or 16 GB is enough.