Why is my Mac storage filling up by itself?
By Vishva Variya · Updated · 6 min read
Short answer
Usually something is quietly growing: app caches, local Time Machine snapshots, iCloud files downloading, Mail and Messages attachments, Xcode and developer data, downloaded AI models or a sync app. Compare System Settings › General › Storage today and in a few days, and check which folders grew in your home folder’s Library.
What makes Mac storage grow on its own?
- App caches: browsers, Spotify, Slack, Teams and creative apps can each keep gigabytes in ~/Library/Caches.
- Local Time Machine snapshots: kept on the startup disk while your backup drive is away. macOS removes them when it needs space.
- iCloud Drive and Photos: files download when opened and stay until macOS frees them, or permanently if Optimise Mac Storage is off.
- Mail and Messages: attachments are saved on the Mac, often years of them.
- Xcode and developer tools: build data, simulators and device support grow with every project and iOS version.
- AI models: Apple Intelligence keeps its models under System Data, and tools like Ollama and LM Studio store large models in your home folder.
- Sync apps: Google Drive, Dropbox and OneDrive keep downloaded copies of files you open.
How do I find what’s taking up space?
- 1Open System Settings › General › Storage and note the bar’s categories.
- 2Click ⓘ beside a category to see its largest items.
- 3In Finder, press ⇧⌘G, go to ~/Library, choose View › Show View Options and tick Calculate All Sizes, then sort by Size.
- 4Repeat in a few days. The folder that grew is your answer.
If most of it is System Data, see why System Data is so large. For a folder-by-folder view, see how to see folder sizes.
How do I check for local Time Machine snapshots?
Snapshots count towards System Data and are freed automatically when space runs low, so they’re rarely the real problem. To see them, run this in Terminal; connecting your backup drive and letting a backup finish usually clears them.
tmutil listlocalsnapshots /How do I stop storage filling up again?
- Turn on System Settings › General › Storage › Optimise Mac Storage (Store in iCloud) so iCloud files can be removed locally.
- Clear caches occasionally: see how to clear cache on a Mac.
- Delete Xcode build data and old simulators: see how to clear Xcode cache.
- Remove old downloads and installers every month.
- Remove AI models you don’t use: see Apple Intelligence storage.
Seeing what grew with Peekaboo
Peekaboo measures your folders once a day and keeps those figures on your Mac for 90 days. What Grew This Week, on Home, shows the folders that took the most space over the last week or month, so “something is filling my disk” becomes a folder name. The low-space alert says roughly when the disk fills up at the current rate. From there, Space Map and Clean Up show what each gigabyte is, and every cleanup can be undone.
- 1Open Home and look at What Grew This Week.
- 2Click a folder to see what’s inside it.
- 3Open Clean Up to free space you can put back.⇧⌘K
Questions
Why does my Mac say storage is full when I’ve deleted files?
- Empty the Trash; until then files still take space. Then wait a moment: macOS updates the Storage figure slowly, and local snapshots may still hold deleted files until they expire.
Is it safe to delete ~/Library/Caches?
- Mostly, since apps rebuild caches, but quit the apps first and expect them to be slower, or ask you to sign in, the first time. Don’t delete other Library folders the same way.
How much free space should a Mac have?
- Aim for 10–15% of the disk, and at least 20–30 GB for macOS updates.