A Mac that used to feel instant and now hesitates is frustrating, but the cause is rarely mysterious. Why is my Mac so slow almost always comes down to a handful of overlapping issues: a startup disk that's nearly full, an app quietly burning CPU or memory, too many things launching at login, and years of caches and leftovers nobody ever cleared. The good news is that a Mac running slow is usually a software problem — and software problems are fixable, often for free.
This guide on how to fix a slow Mac shows how to diagnose each cause with the tools already on your Mac, fix it by hand, and decide when it's worth letting a careful cleaner do the tedious parts.
First, find out what's actually slow
Before you delete anything, look at what your Mac is doing right now. Open Activity Monitor (press Command and Space, type its name, hit Return) and check three tabs:
- CPU — click the % CPU header to sort high to low. A process pinned near 100 percent that you didn't start is a prime suspect.
- Memory — check the Memory Pressure graph at the bottom. Green is fine; sustained yellow or red means you're out of RAM and macOS is swapping to disk, which feels like molasses.
- Disk and Network — constant activity here can point to a sync client (cloud storage, photo backup) or an indexer working through your files.
If you spot a stuck app, select it and click the Stop (octagon) button, then relaunch it cleanly. This one check explains most "slow all of a sudden" cases.
The biggest culprit: a full startup disk
Nothing slows a Mac like a nearly-full drive. macOS needs free space for virtual memory, temporary files, and app caches; when it runs out, performance falls off a cliff. The fastest way to speed up a Mac is usually to free space, so aim to keep at least 10–15 percent of your disk free.
To see where space went, open System Settings, then go to General > Storage. The colored bar breaks usage down by category, and the list below it lets you drill in. Quick wins live here:
| Where it hides | What to do |
|---|---|
| Large & old files | Use Finder's search, or Storage recommendations, to find big files you forgot |
| Downloads folder | Open the Downloads folder in Finder, sort by Size, delete installers and archives |
| Old caches & logs | Clear app caches in ~/Library/Caches (see below) |
| Leftover app files | Removing an app's .app leaves prefs and support files behind |
| Duplicate files | Identical copies of photos, documents, and exports add up fast |
Empty the Trash when you're done — files there still count against your disk until you do.
Clear caches and leftovers (carefully)
Caches are temporary files apps create to work faster, useful until they grow stale or
huge. To clear user caches by hand, open Finder, press Command + Shift + G, paste
~/Library/Caches, and press Return. You'll see one folder per app; move the contents
of folders for apps you recognize to the Trash, and the app rebuilds what it needs on
next launch.
Two cautions matter here:
- Don't touch
/Systemor/Librarysystem caches unless you know what a file does. User caches in~/Library/Cachesare the safe layer. - Some "caches" are real data. A music app's offline downloads or a sync database can live in a cache-like folder; deleting it means re-downloading gigabytes or losing local state.
The other quiet space-eater is app leftovers. Dragging an app to the Trash removes
the .app bundle but leaves preferences, Application Support folders, login items, and
caches scattered across your Library. Over years these orphaned files pile up, and some
keep launching at startup.
Tame login items and reclaim startup speed
If your Mac is slow right after you log in, you have too many launch agents. Go to System Settings > General > Login Items & Extensions. In the Open at Login list, remove anything you don't need running immediately, and under Allow in the Background turn off helpers from apps you've since deleted. Fewer startup processes means a snappier login and more free RAM all day.
When to let MacScrub do the digging
Every step above is doable by hand, and for a one-off cleanup it's worth doing yourself. The catch is that the work is repetitive and easy to get wrong — one mistaken Library folder and an app misbehaves. That's the gap MacScrub is built for.
MacScrub scans for the same things you'd hunt for manually — system junk and stale caches, byte-exact SHA-256 duplicates, large and old files, and the complete trail an uninstalled app leaves behind — and explains why each item is safe to remove. Crucially, everything it removes goes to the Trash first, so nothing is gone for good until you empty it. Built-in guards skip things you'd miss, like a music app's offline cache or your latest Xcode device-support files, and the cleaning rules are open source on GitHub — no telemetry, no trackers, no background daemons.
It won't turn a 2014 spinning-disk Mac into an M-series machine. But for the common case — a capable Mac choked by a full disk and years of clutter — it does safely in minutes what would otherwise be an afternoon of folder-spelunking.
A quick recovery checklist. Whichever route you take, work through this in order:
- Activity Monitor — quit any runaway CPU or memory hog.
- Free disk space — get back above 10–15 percent free; this matters most.
- Clear user caches in
~/Library/Caches, then empty the Trash. - Remove app leftovers from apps you've deleted.
- Trim login items so fewer things launch at startup.
- Restart to clear memory and let macOS finish housekeeping.
Work top to bottom and most slow Macs come back to life. When you'd rather skip the digging — or keep things tidy without thinking about it — MacScrub runs the same checklist for you, and sends every removal to the Trash so it's always recoverable.