If your Mac just showed you the alert "Your startup disk is almost full," you are not alone — and you do not need to buy a new Mac or an external drive. This guide walks through 9 proven fixes to free up space on a full Mac startup disk, ordered from the safest and fastest to the more thorough, with honest notes on what each step actually recovers and what you should leave alone.
Why Does the "Startup Disk Almost Full" Warning Appear?
macOS watches your startup disk's free space and shows the warning when you drop below roughly 1–2 GB. At that threshold, the system can no longer write swap files, decompress software updates, or handle normal temporary I/O — your Mac slows to a crawl, apps crash, and in extreme cases you cannot log in. The fix is not to ignore it.
The disk space typically disappears into a few buckets:
- System Data / purgeable space — caches, iOS backups, Time Machine local snapshots, and APFS purgeable reserves that macOS calls "System Data" in About This Mac.
- User caches and logs — app-level caches that grow without bound in
~/Library/Cachesand system logs in/private/var/log. - Large media and downloads — files you forgot about in
~/Downloads,~/Movies, or iCloud Drive. - App leftovers — preference files, plugins, and support bundles from apps you deleted years ago.
- Trash — files that are logically deleted but still consume physical space.
Fix 1: Empty the Trash (Immediately, 0–5 GB)
This is the single fastest win. Right-click the Trash icon in the Dock and choose Empty Trash. If you use multiple users or any apps that maintain their own trash (iPhoto, Final Cut), check those too. Some large files — like movies you dragged to Trash — sit there for months.
Risk: None. Files in the Trash are ones you already chose to remove.
Fix 2: Clear Your Downloads Folder (0–20 GB)
Open ~/Downloads and sort by Size. Disk images (DMG), ZIP archives of apps you already installed, and old Zoom or Teams installers are common offenders. Bulk-select anything you recognise and no longer need, then delete and empty Trash again.
Risk: Low. Only delete files you recognise. When in doubt, leave it.
Fix 3: Delete iOS and iPhone Backups (2–50 GB)
iTunes (macOS Catalina and earlier) and Finder (macOS Big Sur and later) store full iPhone and iPad backups locally. Go to Finder → your iPhone in the sidebar → Manage Backups, or open System Settings → General → Storage → iOS Files on macOS Ventura and later. Delete backups for devices you no longer own. Keep at least the most recent backup for any device you care about, or confirm iCloud Backup is on first.
Risk: Low–Medium. Deleting a backup means you cannot restore to that snapshot. Make sure iCloud Backup is enabled before deleting a local backup.
Fix 4: Remove Time Machine Local Snapshots (1–20 GB)
APFS takes hourly snapshots to enable Time Machine even when your backup drive is disconnected. These are "purgeable" — macOS should remove them when space is low — but they do not always clear fast enough. You can speed this up manually in Terminal:
tmutil listlocalsnapshots /
tmutil deletelocalsnapshots YYYY-MM-DD-HHMMSSReplace the timestamp with each snapshot you want to remove, or loop through them. On macOS Sonoma and later you can also delete them from System Settings → General → Storage → Time Machine Snapshots.
Risk: Low. Local snapshots are redundant copies. Your actual Time Machine backup on an external drive is unaffected.
Fix 5: Clear System and User Caches (1–10 GB)
macOS and apps store temporary cached data that should be rebuilt on demand. The main locations are:
~/Library/Caches— per-user app caches (Safari, Xcode derived data, Homebrew, etc.)/Library/Caches— system-level caches (requires admin password)~/Library/Logsand/private/var/log— logs that grow over months
You can open the folder in Finder with Go → Go to Folder (Shift+Cmd+G) and manually inspect. However, deleting the wrong cache (e.g. an active app's SQLite database inside its cache folder) can cause that app to misbehave. The safer approach is to quit an app, delete its cache subfolder, then relaunch.
If you want to handle caches, logs, and purgeable space in one step without hand-editing system folders, Crumb does exactly this — it runs on-device heuristics to identify what is safe to clear and does it with one click, then shows you exactly how much each category freed.
Risk: Low for most caches. Apps rebuild their caches; the only downside is a slightly slower first launch. Do not delete the entire ~/Library folder or anything in /System.
Fix 6: Find and Remove Large Files (Varies)
macOS Ventura and later offer a decent built-in view: Apple menu → System Settings → General → Storage. Click any category to browse large files.
In Terminal, you can find the largest items in your home folder:
du -sh ~/Downloads/* | sort -rh | head -20Common culprits: old virtual machine images (.vmdk, .sparseimage), Xcode simulators (~/Library/Developer/CoreSimulator), Final Cut Pro render files, and Logic Pro audio projects.
Risk: Low if you recognise the file; Medium if you do not. The Crumb Visualize view renders an interactive treemap of your entire disk so you can see exactly what is eating space before you delete anything — useful when Terminal output is too cryptic.
Fix 7: Uninstall Apps You No Longer Use (0–5 GB per app)
Dragging an app to Trash in macOS leaves behind support files, preferences, caches, and sometimes launch agents scattered across your Library. A genuinely clean uninstall requires removing all of those. Common leftover locations:
~/Library/Application Support/AppName~/Library/Preferences/com.developer.AppName.plist~/Library/LaunchAgents/com.developer.AppName.plist/Library/Application Support/AppName(system-wide)
You can search these manually, or use the Uninstall tab in Crumb which locates all leftover files associated with an app and lets you review them before removal.
Risk: Low. Preference files are tiny but numerous; removing them just means the app resets to defaults if you reinstall it.
Fix 8: Offload iCloud Drive and Optimize Storage (Varies)
If you use iCloud Drive, turn on Optimize Mac Storage in System Settings → Apple ID → iCloud → iCloud Drive → Options. macOS will keep only recently accessed files locally and stream older ones on demand. Similarly, for Photos, enable Optimize Mac Storage in Photos → Settings → iCloud.
Risk: None, as long as you have a reliable internet connection. Files are not deleted — they are stored in iCloud and re-downloaded when you open them.
Fix 9: Move Files to External Storage or NAS (Largest Gains)
For media-heavy workflows — video editors, photographers, music producers — no amount of cache clearing will solve the underlying problem if your project files live on the boot drive. Moving your ~/Movies, ~/Music, or project folders to an external SSD or NAS is the only sustainable fix. Use Finder to move the folder, then create a symlink so apps that expect the default location still work:
mv ~/Movies /Volumes/ExternalDrive/Movies
ln -s /Volumes/ExternalDrive/Movies ~/MoviesRisk: Medium. Make sure the external drive is reliably connected and backed up. A broken symlink can confuse some apps.
What You Should NOT Delete
A quick honest note on what to leave alone:
/System,/Library,/usr,/private— system-owned directories that macOS depends on. SIP (System Integrity Protection) prevents most accidental deletions here, but do not try to bypass it.~/Library/Keychains— your passwords live here.- Anything you cannot identify. Use the Is this safe to delete? feature in Crumb to get an explanation before removing unfamiliar folders.
Quick Reference: What Each Fix Typically Recovers
| Fix | Typical Space Freed | Risk |
|---|---|---|
| Empty Trash | 0–5 GB | None |
| Clear Downloads | 0–20 GB | Low |
| Delete iOS backups | 2–50 GB | Low–Medium |
| Remove Time Machine snapshots | 1–20 GB | Low |
| Clear caches and logs | 1–10 GB | Low |
| Find and remove large files | Varies | Low–Medium |
| Uninstall unused apps + leftovers | 0–5 GB per app | Low |
| Optimize iCloud storage | Varies | None |
| Move media to external storage | 10–500+ GB | Medium |
Keeping Your Startup Disk Healthy Long-Term
A one-time cleanup is not enough. Caches grow back, logs accumulate, and downloads pile up. Set a reminder to check your storage once a month. If you want to automate the tedious parts — caches, logs, purgeable space — download Crumb and run a one-click clean on a schedule. For everything else, the manual steps above are free and effective as long as you are careful about what you remove.
The "your startup disk is almost full" message is a genuine warning, but it is not a crisis. Work through these nine fixes in order and you will almost certainly recover several gigabytes — often tens of gigabytes — without spending a cent or risking your data.