Why Is My Mac So Slow? How to Find Out and Fix It

Almost every “speed up your Mac” article hands you the same twenty tips and lets you guess which one applies. That's backwards. A slow Mac has a cause, the cause leaves evidence, and two numbers will point at it in about ninety seconds. Read those first, then do only the fix that matches — you'll usually need one, not twenty.

First, the ninety-second diagnosis

Open Activity Monitor (in /Applications/Utilities, or press ⌘ + Space and type its name) and look at exactly two things.

1. The CPU tab. Click the % CPU column header to sort highest-first. Is one process sitting above 80% while you're doing nothing? Write down its name.
2. The Memory tab. At the bottom is a Memory Pressure graph. Green means macOS has memory to spare. Yellow means it's working to keep up. Red means it's out. Next to it, note the Swap Used figure.

Then check free space: System Settings → General → Storage. Now match what you saw to a section below.

1. One process is eating the machine

This is the most common cause and the easiest to fix. In Activity Monitor's CPU tab, sort by % CPU and watch for thirty seconds. A few names come up again and again:

• A web browser — usually one tab, not the browser itself. In Chrome, Window → Task Manager names the guilty tab; Safari's is Develop → Show Web Inspector after you clear website data. See fixing a slow Safari.
• mds, mds_stores, mdworker — Spotlight indexing. Normal after an update or after you copy a lot of files; see section 6.
• photoanalysisd — Photos scanning your library for people and Memories. It only runs when the Mac is idle and plugged in, and it does finish.
• kernel_task — not a runaway process at all. It's macOS deliberately throttling the CPU to control heat.
• An app you forgot was running — a sync client, a video call that never fully quit, an installer waiting on a dialog behind another window.

To read the same list without leaving Terminal:

# Live process list sorted by CPU (press q to quit — changes nothing)
top -o cpu

# Same, sorted by memory
top -o mem

Once you know the name, quit the app normally. If it won't respond, force quit it — and if it's the frontmost window that's stuck, that's the spinning beach ball, which has its own guide.

2. You're out of RAM (yellow or red memory pressure)

When physical memory runs out, macOS starts writing memory pages to the SSD. That's swap, and it's dramatically slower than RAM — it's what makes a Mac feel like it's moving through treacle. The signal isn't the “free memory” number, which is nearly always low on a healthy Mac by design; it's the pressure graph plus Swap Used.

Rough reading: green with under a gigabyte of swap is fine. Sustained yellow with several gigabytes of swap means you're regularly asking for more memory than you have. Red means you're there now.

The fixes, in order of effect: close browser tabs (they are usually the single biggest consumer), quit apps you're not using rather than minimising them, and restart — a restart clears swap and any process that has slowly leaked memory over days of uptime. The full guide to freeing up RAM covers what works and which tricks are placebo, and memory pressure explained goes deeper on reading the graph.

3. The startup disk is too full

macOS needs free space to swap, cache, and stage updates. Once the boot volume gets close to full, everything slows at once — and a truly full disk can stop apps saving at all. Aim to keep at least 10–15% of the drive free, or roughly 15–20 GB, whichever is larger.

# How much space is actually free on the data volume
df -h /System/Volumes/Data

Start with System Settings → General → Storage, which breaks usage down by category and offers built-in recommendations. Then work through the Downloads folder, your largest files, and duplicates. If the “System Data” block looks enormous, that category has a specific explanation — it's usually local Time Machine snapshots, which macOS counts as purgeable. The full walkthrough is in what to do when the disk is almost full.

4. It's only slow for the first few minutes

If the Mac is fine once it settles, the problem is login, not the machine. Every app that opens at login competes for CPU and disk at exactly the same moment.

1. Open System Settings → General → Login Items (called Login Items & Extensions on macOS 15 Sequoia and later).
2. Under Open at Login, remove anything you don't need on screen the second you log in.
3. Scroll to Allow in the Background. This is the list people miss — updaters, sync agents, and helpers installed by apps you may have deleted years ago. Switch off anything you don't recognise; you can switch it back on if something breaks.

Then stop macOS restoring every window you had open last time, which can mean a dozen apps launching before you've touched anything: turn off reopening windows. The startup items guide covers the older login-item locations too, and slow boot deals with the case where it's the boot itself that drags.

5. Nothing is wrong — it just feels slow

On a Mac more than a few years old, a real part of the sluggishness is drawing time: window animations, translucent menus, the Mission Control zoom, the Dock's launch bounce. None of it makes the Mac work faster or slower in any benchmark sense, but cutting it removes the wait you actually feel.

The two with the biggest payoff are in System Settings → Accessibility → Display: Reduce motion and Reduce transparency. From Terminal:

# Instant window open/close — no animation
defaults write NSGlobalDomain NSAutomaticWindowAnimationsEnabled -bool false

# Undo
defaults delete NSGlobalDomain NSAutomaticWindowAnimationsEnabled

See disable animations, reduce transparency, speed up Mission Control, and speed up the Dock. On a genuinely old machine, work through the old-MacBook guide instead — the priorities are different.

6. It started right after a macOS update

This one is usually not a fault. After a major update, macOS re-indexes Spotlight, re-analyses your photo library, and re-verifies apps on first launch. It's genuinely slower for a day or two and then it isn't. Leave the Mac plugged in and awake overnight before you go hunting. What's normal after an update explains how to tell the difference between settling and stuck.

7. When it's the hardware

Some slowness isn't fixable in software. A Mac with 8 GB of memory running a browser, a chat app and a design tool will swap no matter how carefully you tune it — and on Apple silicon, memory is soldered, so more RAM means a different Mac. Similarly, a spinning hard drive in a pre-2013 machine is a hard ceiling.

Heat is the other hardware-shaped cause: a Mac that's throttling because it can't shed heat will feel slow in a way no setting fixes. If yours runs hot or loud, see MacBook overheating and fans always running. And run Disk Utility → First Aid once to rule out filesystem damage — here's how.

What not to do

• Don't install a “cleaner”. The things they charge a subscription for — emptying caches, deleting language files, “optimising” RAM — are either done by macOS already or have no measurable effect. We wrote about whether Mac cleaner apps are worth it at length.
• Don't run memory “boosters”. Freeing cached memory doesn't help; macOS caches on purpose and gives the memory back the instant something needs it. Running sudo purge just makes the next few minutes slower while the cache refills.
• Don't delete caches at random. They rebuild, which costs you time and disk writes. Clear a specific app's cache when that app misbehaves — see clearing caches safely.

The settings-level fixes above are one-click, reversible toggles in Mainspring — labelled in plain English, with an undo button for every one.

Common questions

How do I know if my Mac is slow because it needs more RAM?

Open Activity Monitor and look at the Memory tab. If the Memory Pressure graph sits in yellow or red during normal use and Swap Used is several gigabytes, you're regularly asking for more memory than the Mac has. If pressure stays green, more RAM would not help and the cause is elsewhere.

Does restarting a Mac actually make it faster?

Sometimes, and for real reasons: a restart clears swap, ends processes that have leaked memory over long uptimes, and releases files held by crashed apps. It is not a cure for a full disk or an app that pins the CPU, but it is a legitimate first step and costs a minute.

Will a cleaner app speed up my Mac?

Almost never. macOS already manages its own caches and memory. Cleaners mostly delete files that rebuild themselves, and the disk space they recover is usually available through System Settings' own storage tools for free.

How much free disk space does macOS need?

Keep at least 10-15% of the startup disk free, or 15-20 GB, whichever is larger. Below that, macOS runs short of room for swap and caching and the whole system slows down.

Why is my Mac slow even though Activity Monitor shows low CPU?

Low CPU with slowness usually points at memory or disk rather than processing. Check memory pressure and swap first, then free space on the startup disk. If both are healthy, the sluggishness is likely interface animation, which you can turn down in Accessibility settings.