Speed up your Mac
Why Is My Mac So Slow? 12 Real Causes (And How to Fix Each)
A slow Mac usually has a specific cause, not a vague one. Here are the 12 most common reasons your Mac is dragging — and the exact fix for each.
The frustrating thing about a slow Mac is that it’s almost never one big problem. It’s six small ones stacked on top of each other — a runaway browser tab, a forgotten launch agent from an app you uninstalled in 2023, a Spotlight reindex no one asked for, 14GB of cached video thumbnails, and so on. Each one alone is invisible. Together, they turn a perfectly good machine into something that takes eight seconds to open Finder.
Honestly, most of what people call “my Mac is old” is actually “my Mac has accumulated junk.” Here are the 12 actual causes I see over and over, ranked roughly by how often they’re the real culprit, with the fix for each.
1. Your startup disk is nearly full
macOS leans hard on free disk space. Once you drop below about 15% free, the system starts struggling with swap memory, virtual memory paging, and Time Machine local snapshots. Sonoma 14 and Sequoia 15 both get noticeably sluggish under tight storage.
Check it: Apple menu → System Settings → General → Storage. If you’re below 20GB free on the system drive, that’s almost certainly the bottleneck.
The manual fix is to dig through Downloads, empty Trash, clear browser caches, and find the giant video files you forgot about. It works — it just takes an hour.
2. Browser tabs are eating your RAM alive
Open Activity Monitor (Spotlight: “Activity Monitor”), sort by Memory. If Chrome Helper, Safari, or Arc are pulling more than 8GB combined, you’ve found a major slowdown source. Each modern web app — Notion, Figma, Gmail, Slack web — easily takes 400-800MB per tab.
Close tabs you haven’t touched in two days. Use a tab manager extension. Or just be honest with yourself about which 30 tabs you’re never going back to.
3. Login items are launching apps you don’t need
Every app you’ve installed has a chance of sneaking something into your login items. Adobe Creative Cloud, Microsoft AutoUpdate, Spotify, Dropbox, Zoom — they all want to start at boot. Five minutes after login, you’ve got 17 background processes running before you’ve opened anything.
Go to System Settings → General → Login Items & Extensions. Disable anything you don’t actively need at startup.
4. Caches that should’ve been cleared months ago
Every browser, every app, and macOS itself maintains caches. They’re supposed to make things faster. In practice, they grow indefinitely until they slow you down.
The usual suspects:
~/Library/Caches/com.apple.Safari— can hit 5-10GB~/Library/Caches/Google/Chrome— often 3-8GB~/Library/Caches/com.spotify.client— surprising amount, usually 2-4GB~/Library/Logs— log files that nobody ever reads
You can clear these by hand in Finder. The risk is deleting something an app actually needs and having to reset preferences.
5. Spotlight is reindexing in the background
If you’ve recently added a big folder, restored from backup, or installed Sonoma over an existing system, Spotlight might be rebuilding its index. This eats CPU and disk I/O for hours, sometimes days on slower drives.
Check Activity Monitor for processes named mdworker, mds, or mds_stores. If they’re using significant CPU, Spotlight is the cause.
You can wait it out, or exclude folders that don’t need to be searchable in System Settings → Siri & Spotlight → Spotlight Privacy.
6. macOS hasn’t been restarted in weeks
I know. The whole point of a Mac was that you never had to reboot. But on Sonoma and Sequoia, memory leaks in WindowServer and various background daemons are real. If your uptime is 21 days, just restart. It probably fixes 30% of slowdowns by itself.
7. Old apps are running on Rosetta
Apple Silicon Macs translate Intel apps via Rosetta 2. It’s clever, but it’s not free — Rosetta apps use more memory and CPU. If you’re on an M1/M2/M3 and still running an Intel-only build of, say, Microsoft Office or some niche utility, you’re paying a tax.
Check in Activity Monitor: the “Kind” column shows “Apple” or “Intel.” Update or replace any Intel apps you can.
8. Background sync from cloud services
Dropbox, iCloud Drive, OneDrive, Google Drive — when these are syncing, they hammer the disk and network. If you’ve recently added a large folder, expect hours of slowness while they catch up.
Pause sync temporarily if you need performance now. iCloud Drive doesn’t have a clean pause, but you can sign out and back in to throttle it.
9. Leftover files from apps you uninstalled
Dragging an app to Trash doesn’t remove its support files, preferences, or login agents. Five years of installs and uninstalls means hundreds of MB — sometimes GB — of dead files in ~/Library/Application Support, ~/Library/Preferences, and ~/Library/LaunchAgents.
Some of those launch agents are still trying to start, fail, and eat CPU. The truly dedicated can hunt them by hand. Most people give up partway.
10. Photos library doing background analysis
After you import a batch of photos, the Photos app spends days analyzing faces, places, scenes, and Memories in the background. The process is photoanalysisd and it’s notoriously CPU-hungry.
There’s no clean way to disable it without losing those features, but you can limit it: don’t import while you need performance, and let it run overnight.
11. Visual effects you can turn off
This barely matters on M-series Macs but absolutely matters on older Intel models. System Settings → Accessibility → Display → Reduce Motion and Reduce Transparency both speed things up perceptibly on older hardware.
The Dock’s bouncy animations, Mission Control transitions, and window genie effects all take GPU cycles. On a 2017 MacBook Pro, turning them off is the difference between usable and painful.
12. The drive is actually failing
If your Mac is more than five or six years old and getting dramatically slower over weeks or months, the SSD might be on its way out. Run Disk Utility’s First Aid (Applications → Utilities → Disk Utility). If it reports errors, back up immediately.
A real diagnostic order
If you’re not sure where to start, do this in order:
- Restart the Mac. Seriously.
- Check storage —
System Settings → General → Storage. Free up space if under 15%. - Open Activity Monitor and sort by CPU, then Memory. Note what’s at the top.
- Disable login items you don’t need.
- Clear caches — by hand or with a tool.
- Quit cloud sync apps temporarily and see if things improve.
- Run Disk Utility’s First Aid.
That sequence resolves about 90% of “my Mac is slow” cases I’ve seen.
Where Sweep fits
Most of what’s above can be done by hand if you’ve got the time and patience. Sweep is what we built when we got tired of doing the same hunt every two months — it scans for caches, logs, language files, leftover support files from uninstalled apps, and oversized forgotten files all at once. It shows you exactly what it found, you tick what to remove, and it’s done.
What it doesn’t do: scan for malware (we’re a cleaner, not antivirus), magically make a 2014 MacBook Air feel like an M3, or fix a failing SSD. But for the eight or nine things on this list that are about accumulated junk, it does in 90 seconds what would otherwise take an hour.
A slow Mac almost always has a specific, fixable cause. Work through the list, restart between steps, and don’t assume hardware until you’ve ruled out software. Most “old, slow Macs” have years left in them.