Time Machine local snapshots: what they are, how to delete

What a local snapshot is

When Time Machine is turned on, macOS regularly takes a snapshot of your startup disk using a feature of APFS, the Mac's file system. A snapshot is not a folder and not a second copy of your files. It is a record that says: keep everything exactly as it was at this moment.

Snapshots let you restore a file you changed or deleted an hour ago, even if your backup drive is not connected. Time Machine also uses them to make its backups consistent.

Why they take up space

A new snapshot takes almost no space, because nothing has changed yet. The cost appears later. When you delete or overwrite a file, the old data cannot be released while a snapshot still refers to it.

This is the usual reason behind a confusing situation: you delete a large folder, empty the Trash, and free space barely moves. The files are gone from view but are held by a snapshot until it expires.

macOS treats this space as purgeable. Finder includes it in the available figure, and the system gives it back when something needs the room. So snapshots rarely stop you saving files, even when the numbers look alarming.

List the snapshots on your Mac

Open Terminal and run the command below. It only lists. Each line ends with a date and time, which is the snapshot's name for the purposes of deleting it.

You can also see them in Disk Utility. Choose View, then Show APFS Snapshots, and select your data volume in the sidebar. The table at the bottom shows each snapshot with its creation date and how much space it holds privately.

Not everything in that list comes from Time Machine. macOS creates its own snapshot when it installs an update, and some backup apps create theirs. Leave any snapshot you do not recognise as a Time Machine one alone.

tmutil listlocalsnapshots /

When to leave them alone, and when to delete

Leave them alone in the normal case. They are removed automatically after roughly a day, and sooner under pressure. Waiting costs nothing and keeps your safety net.

Deleting one is reasonable in a few situations:

• You need a large amount of space right now, for example to install a macOS update or copy a big project, and the installer or app does not trigger the automatic cleanup.
• You have just deleted a lot of data on purpose and want the free space figure to reflect it immediately.
• A tool that reads free space directly, such as a disk partitioning or virtual machine app, refuses to continue because it does not count purgeable space.

Delete snapshots with tmutil

To delete a single snapshot, take the date stamp from the list and pass it to deletelocalsnapshots, as in the first line below. Replace the example date with one from your own list. Only that snapshot is removed.

To let macOS decide, use thinlocalsnapshots, shown in the second line. It asks the system to free up to the given number of bytes from snapshots, here 20 billion, which is 20 GB. The final number is the urgency, from 1 to 4, with 4 the most aggressive. Oldest snapshots go first.

Check the result with tmutil listlocalsnapshots / again. The free space shown in Finder can take a moment to catch up.

tmutil deletelocalsnapshots 2026-10-10-093015
tmutil thinlocalsnapshots / 20000000000 4

Delete a snapshot in Disk Utility

If you prefer not to use Terminal, Disk Utility can do the same. Choose View, Show APFS Snapshots, select the data volume, click the snapshot in the table and click the minus button below it, then confirm.

Whichever way you use, what you lose is the ability to restore files as they were at that moment from the Mac itself. Backups already saved to your Time Machine drive are not affected, and Time Machine goes on taking new snapshots on schedule.

Do not turn Time Machine off to prevent snapshots. They are a side effect of having backups, and the backups are what matter.

How Diskzy shows snapshots

Diskzy's System Data view breaks macOS's System Data into named parts, each with its size and a label. Snapshots appear there marked Managed by macOS, and Diskzy does not offer to delete them.

That is the point of the view: it tells you how much of your System Data is snapshot space that will come back by itself, and how much is something you can act on.