'Your Disk Is Almost Full' on Mac: What to Do

macOS shows "Your disk is almost full" when free space on the startup disk drops to the last few gigabytes — right around the point where swap files grow cramped, updates refuse to install, and everything gets slower. Here's how to claw back space in minutes, then keep the warning from coming back.

Take the quick wins first

Before analyzing anything, grab the space that's almost always sitting there:

1. Empty the Trash: click and hold the Trash icon in the Dock and choose Empty Trash. Deleted files hold their full size until you do.
2. Open ~/Downloads in Finder, click the Size column to sort largest first, and delete old installers, .dmg disk images, and zip files you've already extracted.
3. Delete outdated iPhone and iPad backups: connect the device, select it in a Finder window's sidebar, click Manage Backups, and remove old entries. Each one can be tens of gigabytes.
4. Restart the Mac. macOS clears swap and various temporary files on boot, which alone can settle a machine that's been up for weeks.

See where the space actually went

Open System Settings → General → Storage (same path on macOS 13 Ventura, 14 Sonoma, and 15 Sequoia). The colored bar shows usage by category, and the list below it breaks down Applications, Documents, Photos, and the rest — click the ⓘ next to a category to see and delete individual large files without leaving Settings. The Recommendations section up top offers Store in iCloud, Optimize Storage, and automatic Trash emptying; the last one is the safest instant win.

Two categories deserve special attention. If Photos dominates, don't delete pictures — turn on optimized storage or move the library to an external drive instead. And a large System Data slice usually means caches, snapshots, and old device backups rather than anything you can see in Finder; it has its own cleanup playbook.

Clear snapshots and purgeable space

If the numbers still look wrong — you deleted plenty but "available" barely moved — local Time Machine snapshots are usually holding the freed blocks:

# see whether snapshots exist on the startup disk
tmutil listlocalsnapshots /

# thin them aggressively to reclaim space now
tmutil thinlocalsnapshots / 999999999999 4

This is low-risk: local snapshots expire within 24 hours anyway, and Time Machine immediately resumes its hourly schedule, so new restore points reappear on their own. Purgeable space (evicted iCloud files, caches) also releases itself as pressure rises — give it time before assuming something's stuck.

How much headroom to keep

Aim to keep roughly 10–15% of the disk free — on a 256 GB Mac, that's 25–40 GB. macOS needs the room for virtual-memory swap, app caches, and updates (a major macOS upgrade alone wants over 12 GB free). Run consistently below that and you'll feel it as spinning cursors and stalling apps long before the warning appears. A monthly Downloads sweep plus automatic Trash emptying keeps most Macs permanently clear of the threshold.

Make the fix permanent

The single best set-and-forget move is letting macOS empty the Trash on its own schedule — files older than 30 days go automatically. How to turn it on, and the recovery trade-off to know about first, is in auto-empty the Trash on Mac after 30 days.