If you back up with Time Machine, your Mac also keeps backups on its own disk: local snapshots. They let you restore a file you changed or deleted an hour ago, even while your backup disk is somewhere else.
They're also the most common reason a Mac's storage doesn't add up. A snapshot holds on to everything that changed or was deleted since it was taken, and no folder shows that space. Delete a 40 GB video and the space may not come back, because a snapshot still holds it.
How long they stay
When Back Up Automatically is on, Time Machine saves a snapshot of your startup disk about every hour and keeps each one for 24 hours. It also keeps a snapshot of your last successful backup, and macOS saves one before each update.
Your Mac counts the space snapshots hold as available, and Time Machine removes them as they age or when the space is needed. So most of the time they sort themselves out. They get in the way when something needs a lot of space at once, such as a macOS update, a large download or a video export, faster than macOS clears them.
Seeing them
Open Disk Utility, choose View › Show APFS Snapshots, and select your startup disk's volume in the sidebar. The snapshots appear in a list at the bottom of the window, each with its name, which includes its date, and when it was made. Snapshots named com.apple.TimeMachine… are Time Machine's; others come from macOS updates or from other backup apps.
Snapshots share most of their data with each other and with your files, so there's no simple size for each one, and removing one often frees less than you'd expect.
Removing them
To remove one snapshot: in Disk Utility's snapshot list, select it, click Delete Snapshot, and confirm. Choose View › Hide APFS Snapshots when you're done.
To have Time Machine remove its snapshots now: open Apple menu › System Settings, click General, then Time Machine. Click Options, set Backup Frequency to Manually and click Done, wait a few minutes, then set it back. Time Machine removes its local snapshots when it stops backing up automatically, and starts again with the next backup.
What it costs: you can no longer restore files from the removed snapshots. Backups on your Time Machine disk aren't affected.
When there's no backup disk any more
If you stopped using a Time Machine disk, Time Machine can keep trying to back up and keep making snapshots. Turn off Back Up Automatically, or remove the old disk in System Settings › General › Time Machine, so it stops.
How the app does it
The app's space meter shows how much of your disk's available space is purgeable and how many local snapshots there are, so you can see when snapshots are holding space. Its System Data › Local Snapshots page lists every snapshot: when it was made, which app made it, and whether macOS removes it by itself.
When you choose, the app deletes only Time Machine's own snapshots, with Time Machine's own tool. It can also ask Time Machine to remove as many as it can, and the confirmation says that usually means all of them. Both need an administrator's name and password, through the helper. Because macOS doesn't say what a snapshot holds, the app measures available space before and after, and shows the difference.
What the app runs, after you review itPRO
- tmutil deletelocalsnapshots <date>
- One of Time Machine's local snapshots
- tmutil thinlocalsnapshots / <size> 4
- Asks Time Machine to remove as many as it can
Seeing your snapshots is free. Removing them from the app is PRO.
Safe to delete?
The entries this guide is about, in the words the app shows. Each has its own page with its sources.
Hourly snapshots of your startup disk that Time Machine keeps on the disk itself, so you can restore files even without your backup disk.
Managed by macOS · Runs tmutil for Time Machine's own snapshots, through the helper