Why Is My Mac Running Slow? 10 Real Causes and How to Speed It Up
A Mac rarely gets slow for no reason. It's usually one of a short list of causes, and most of them show up clearly in tools that are already on your Mac. The trick is to diagnose before you start deleting things or installing "speed-up" apps, because the fix for a full disk is completely different from the fix for an overheating MacBook.
Quick answer: Start by restarting your Mac and installing any pending updates. Then check three things: free disk space (System Settings → General → Storage), memory pressure (Activity Monitor → Memory; yellow or red means you're short of RAM), and what launches at login (System Settings → General → Login Items & Extensions). A nearly full startup disk, too many background apps and one runaway process explain most slow Macs. If it's slow only for a few hours after a macOS update, that's usually Spotlight re-indexing, and it settles down on its own. MacCove Space shows storage, memory pressure, CPU and login items in one window, which makes it quicker to tell which of these is slowing you down.
First, work out what kind of slow it is
Different symptoms point to different causes. Matching the symptom first saves a lot of trial and error.
| What you notice | Most likely cause | Where to check |
|---|---|---|
| Everything sluggish, spinning beach ball, apps slow to open | Memory pressure or a nearly full disk | Activity Monitor → Memory; System Settings → Storage |
| Slow for a few hours after a macOS update or migration | Spotlight rebuilding its index (mds_stores) | Activity Monitor → CPU |
| Fans loud, MacBook hot, kernel_task high in CPU | Heat. macOS is deliberately slowing things down to cool the chip | Activity Monitor → CPU; the room and the vents |
| Slow right after you log in, then improves | Too many login items and background apps | Login Items & Extensions |
| One app is slow, everything else is fine | That app (old version, Intel-only, or leaking memory) | Activity Monitor; Finder → Get Info |
| Slow only on battery | Low Power Mode is on | System Settings → Battery |
| Getting worse over months, disk always nearly full | Storage running out, so macOS can't swap | System Settings → General → Storage |
1. Your startup disk is nearly full
This is the most common cause and the one people suspect least. macOS uses free disk space as overflow memory, called swap. When your apps need more RAM than you have, macOS writes some of it to disk. If the disk is almost full there's nowhere to put it, and the whole system slows down or shows "Your startup disk is almost full."
Freeing up storage is the first step in Apple's own advice for a slow Mac. Open System Settings → General → Storage, look at the recommendations, and see how much space is actually free. As a rule of thumb, keep at least 10–15% of the disk free, and more if you work with large video or photo libraries. Major updates need room too: macOS 27 alone took around 30GB more than Tahoe on many Macs.
The hard part usually isn't deleting files, it's finding them. A big share of a full Mac tends to sit in System Data, caches and leftovers from apps you've already removed, none of which Finder shows clearly. Our guide on how to free up disk space on a Mac walks through each of them.
2. You're running short of memory (RAM)
Open Activity Monitor (press ⌘Space, type "Activity Monitor", press Return) and click the Memory tab. The Memory Pressure graph at the bottom matters far more than the "Memory Used" number.
| Memory Pressure colour | What Apple says it means | What to do |
|---|---|---|
| Green | RAM is being used efficiently | Nothing. A Mac using most of its RAM is normal |
| Yellow | The Mac may eventually need more RAM | Quit apps and browser tabs you aren't using |
| Red | The Mac needs more RAM | Close heavy apps now; buy more RAM next time |
Don't worry if "Memory Used" looks nearly full. macOS deliberately fills spare RAM with cached files and compresses memory that apps aren't actively using. What hurts is sustained yellow or red pressure and a growing Swap Used figure. We go deeper in how to check memory usage on a Mac.
3. Too many apps launch at login
Every app that opens at login, and every helper that runs in the background, takes memory and CPU from the moment you sign in. After a year or two of installing software it's easy to collect a dozen: cloud sync clients, updaters, chat apps, mouse and keyboard utilities, VPNs.
To see and trim them:
Open System Settings → General → Login Items & Extensions.
Under Open at Login, select anything you don't need the moment you log in and click –. This doesn't uninstall the app; it just stops it opening automatically.
Review the background section below it. It's called App Background Activity in recent versions of macOS, and was called Allow in the Background from Ventura to Sequoia. Switch off items you don't need, such as updaters for apps you rarely use.
You can also right-click an app's icon in the Dock and choose Options → Open at Login. To test whether login items are the problem, hold Shift while you log in. That skips them for one session.
| Where startup items hide | What lives there | Safe to change? |
|---|---|---|
| Login Items & Extensions → Open at Login | Apps that open when you log in | Yes. Removing them only stops auto-launch |
| Login Items & Extensions → background section | Updaters, sync helpers, agents | Usually. The app may lose a background feature |
| ~/Library/LaunchAgents | Per-user background helpers | With care. Remove only items from apps you've uninstalled |
| /Library/LaunchAgents and /Library/LaunchDaemons | System-wide helpers and services | With care, and only for software you've removed |
| /System/Library/... | macOS itself | No. Never touch these |
Two things make this harder than it should be. The background list often shows only a developer's name, not which app an item belongs to. And items from deleted apps can linger, because dragging an app to the Trash doesn't remove its helpers. If you've uninstalled a lot of software over the years, read how to uninstall apps on a Mac completely.
This is also where a tool saves time. MacCove Space lists login items, launch agents and running background services in one place, shows which app each belongs to, and lets you switch them off without digging through Library folders.
4. Spotlight is re-indexing after an update
If your Mac slowed down straight after a macOS update, a migration from an old Mac, or connecting a large new drive, look for mds_stores or mds near the top of Activity Monitor's CPU tab. That's Spotlight rebuilding its search index, which can take hours on a full disk.
The fix is patience: leave the Mac plugged in and awake for a few hours. If an external drive you never search keeps triggering indexing, add it to Spotlight's privacy list in System Settings → Spotlight.
5. Your Mac is too hot (kernel_task)
When kernel_task is using a lot of CPU, it's tempting to blame it. Don't. Apple explains that one of kernel_task's jobs is to manage CPU temperature by making the CPU less available to processes that are using it intensely. In other words, macOS is slowing things down on purpose so the chip doesn't overheat.
The real fix is to reduce the heat:
Don't run heavy work on a MacBook sitting on a bed, sofa or lap; it needs airflow.
Check the room. Apple's recommended operating range is roughly 10–35°C (50–95°F).
Quit whatever is pushing the CPU hard: a game, a video export, a runaway browser tab.
Don't try to quit kernel_task. You can't, and it would be the wrong fix anyway.
6. One runaway process is hogging the CPU
In Activity Monitor, click CPU and sort by % CPU. If one app or process sits at 100% or more for minutes while you're not using it, that's your culprit. Select it and click the Stop (✕) button. Choose Quit first, which lets the app save its work, and use Force Quit only if it won't respond.
Common offenders are browser tabs running heavy web apps, video calls left open, sync clients stuck on a large upload, and apps with a memory leak.
7. You're running Intel apps on an Apple silicon Mac
Apps built only for Intel Macs run on Apple silicon through Rosetta. It works well, but it's slower and uses more power than a native app. To check an app, select it in Finder, press ⌘I and look at Kind: "Application (Intel)" means it runs through Rosetta.
If an app you use all day is Intel-only, look for a native version. Apple has said Rosetta will be limited to a small set of older games after macOS 27, so those apps need replacing anyway.
8. Low Power Mode is on
On a MacBook, Low Power Mode saves battery by reducing performance. Check System Settings → Battery → Energy Mode, or the battery control in Control Center. It's easy to switch on and forget.
9. Too many browser tabs and extensions
A browser with fifty tabs, a few of them running web apps like Google Sheets, Figma or Slack, can use more memory than everything else on your Mac combined. Bookmark what you need and close the rest, and remove extensions you don't actively use; many of them run on every page you open.
10. macOS or your apps are out of date
Performance bugs get fixed in updates, and some of the worst slowdowns after a major macOS release are fixed in the first point release. Check System Settings → General → Software Update, and update your apps too, especially VPNs, security tools and anything that installs system extensions.
What doesn't really help
A lot of "speed up your Mac" advice is out of date or never worked:
| Common advice | Reality |
|---|---|
| Use a RAM cleaner to free memory | macOS manages memory itself. Forcing it to empty caches usually makes things slower for a while, because those caches have to be rebuilt |
| Clear all caches every week | Caches exist to make things faster. Clearing them helps when one is corrupted or you need the space, not as routine maintenance |
| Defragment the drive | Macs use SSDs, which don't need defragmenting |
| Reset the SMC or NVRAM | On Apple silicon Macs the SMC resets itself; a restart covers it. Manual resets only apply to older Intel Macs |
| Reinstall macOS | Rarely necessary. Try the steps above and Safe Mode first |
If it's still slow: Safe Mode and Apple Diagnostics
Safe Mode starts your Mac without login items and third-party extensions. If the Mac is fast in Safe Mode, something you installed is the problem. On an Apple silicon Mac: shut down, press and hold the power button until you see Loading startup options, select your startup disk, then hold Shift and click Continue in Safe Mode.
Apple Diagnostics checks the hardware. Shut down, disconnect accessories, press and hold the power button until the startup options appear, then press and hold ⌘D.
FAQs
Why is my Mac so slow all of a sudden?
Sudden slowdowns usually come from something that just started: a macOS update triggering Spotlight indexing, a new app adding a background helper, a stuck sync, or the disk crossing into almost-full territory. Check Activity Monitor's CPU tab and your free storage first.
Does clearing the cache speed up a Mac?
Only in specific cases, such as a corrupted cache or a nearly full disk. Otherwise apps simply rebuild their caches and can feel slower for a while. See how to clear cache on a Mac for when it's worth doing.
Is it safe to turn off items in App Background Activity?
Generally, yes. The worst that usually happens is an app loses a background feature, such as automatic updates or syncing while it's closed. You can switch items back on at any time.
How much free space does a Mac need to run well?
Apple doesn't publish a percentage, but keeping 10–15% of the disk free is a sensible target. Major macOS updates also need tens of gigabytes free to install.
Is there one app that shows all of this?
Activity Monitor and System Settings cover the basics, but they're spread across several windows. MacCove Space puts storage, memory, CPU and startup items in one place and gives your Mac a performance score, so you can see at a glance which of the causes above applies to you.