Your Mac is slow. Here is what to actually check

Every list of ways to speed up your Mac opens with the same advice, and most of it is guesswork. Slowness has causes, and they are measurable. Ten minutes with Activity Monitor beats any amount of cache clearing, because it tells you which of four quite different problems you have.

Open Activity Monitor and look at Memory

Applications → Utilities → Activity Monitor, then the Memory tab. Ignore the numbers at the top and look at the Memory Pressure graph at the bottom.

Green means you have enough. Whatever is slow, it is not memory.

Yellow means macOS is compressing memory to cope. Some slowdown, usually tolerable.

Red means the machine is swapping to disk, and everything will feel bad. Look at Swap Used immediately underneath — anything in the gigabytes confirms it.

The fix for red is fewer things running, not a cleaner. Sort the process list by Memory and look at the top five. Browsers with many tabs, Electron apps, virtual machines and image editors dominate. Quitting one heavy app usually returns the graph to green immediately.

Then the CPU tab

Sort by % CPU, highest first, and watch for thirty seconds.

A process sitting at 100% or more when you are not doing anything is your answer. Common culprits, all normal in moderation:

• mds and mds_stores — Spotlight indexing. Heavy after an update or a large file copy, and it finishes. Check with mdutil -s /.
• photoanalysisd — Photos scanning for faces and scenes. Runs after big imports, finishes eventually.
• backupd — Time Machine. Should stop when the backup does.
• kernel_task — often high when the machine is hot; it is macOS deliberately limiting things to cool down.

Anything else at sustained 100% that you cannot name is worth searching by name.

Check the disk is not full

A disk with under 10 GB free makes everything slow, because macOS has nowhere to put swap or temporary files.

df -h /System/Volumes/Data

Under 10 GB free, that is the cause and nothing else matters until it is fixed. The startup disk guide covers it in order.

Check what starts with the machine

If slowness is worst right after login and improves later, you have too much starting at once.

launchctl list | grep -v com.apple

That is the third-party list. System Settings → General → Login Items shows the friendly version. Anything you do not need at login can be switched off, and anything belonging to software you removed is a leftover.

Be realistic about the payoff — this is worth minutes at login, not a transformation. Anyone promising otherwise is selling something.

The four real causes, ranked

In my experience, in order of how often they turn out to be the answer:

1. Not enough memory for what you are running. Red memory pressure. The honest answers are running less at once or a machine with more RAM.
2. A disk that is nearly full. Under 10 GB free.
3. One runaway process. Visible in Activity Monitor within thirty seconds.
4. Thermal throttling. Sustained heavy work, fans loud, kernel_task high. Check nothing is blocking the vents.

What will not help

Clearing caches. Caches make things faster. Clearing them makes the next hour slower.

Disabling swap. It is what stops apps being killed when memory runs out.

“Freeing” RAM. Unused memory is wasted memory; macOS deliberately uses all of it for caching. Tools that “free up RAM” are discarding useful cache to make a number look better.

Repairing permissions. This has not been a thing since El Capitan. The system volume is sealed now.

Resetting the SMC or PRAM. Real fixes for specific hardware symptoms — fans, display, power. Not general performance fixes, and on Apple silicon the SMC reset does not exist.

When it is genuinely the hardware

An eight-year-old Mac running a current macOS is doing more work than it was designed for. If memory pressure is green, the disk has room, no process is running away and it is still slow, you have reached the limit of what tuning does.

Two changes that still help on older Intel machines: replacing a spinning hard drive with an SSD, which transforms them, and adding RAM if the model allows it. Neither applies to Apple silicon, where both are soldered.

CleanSpace shows CPU, memory and disk pressure in the menu bar so you notice the red before you notice the slowness — but Activity Monitor is already on your Mac and tells you the same thing, and knowing which of those four causes you have is the part that matters.