Short answer: Time Machine keeps local snapshots of your startup disk so you can restore files even when the backup drive is not connected. macOS removes them on its own after about 24 hours, or sooner when it needs the space, so you rarely have to act. To see them, run tmutil listlocalsnapshots /. To remove one you no longer want, use sudo tmutil deletelocalsnapshots with its date. Connecting your backup disk and letting a backup finish is the safest first step.
What local snapshots are
A local snapshot is a point-in-time record of your startup disk, kept on that same disk. Because macOS uses APFS, a snapshot does not copy your files; it records which blocks belonged to the disk at that moment. A snapshot only grows when files change afterwards, because the old version of each changed block has to be kept until the snapshot is removed.
When Time Machine is turned on, macOS takes a local snapshot about once an hour and keeps snapshots for roughly 24 hours. It also keeps one from the most recent successful backup. macOS can take a snapshot before installing a software update, so you can return to the state before the update if something goes wrong. Some backup and sync apps create their own APFS snapshots as well.
Snapshots are useful. If you delete a file by mistake while travelling without your backup drive, Time Machine can restore it from a local snapshot. They are not a replacement for a real backup on another disk, because they live on the same drive they protect.
Why they can look like they fill your Mac
The space a snapshot holds depends on how much changed since it was taken. If you downloaded a 40 GB file and then deleted it, the deleted file's blocks may still be held by a snapshot from before the deletion. Finder shows the file as gone, but the free space does not come back until the snapshot is removed.
Storage settings handle this in different ways depending on the macOS version and the moment you look. Snapshot space is often counted as purgeable, meaning macOS can reclaim it when an app needs room, and part of it can appear inside System Data while the snapshots exist. That is why System Data can briefly look larger after you delete large files, then shrink a day later without you doing anything.
See your local snapshots
These commands only read information. They are safe to run at any time.
- Open Terminal.
- List the snapshots on your startup disk:
tmutil listlocalsnapshots /Each line looks like com.apple.TimeMachine.2026-11-07-093015.local. The date and time are in the name. If the command prints only a heading and no names, there are no local snapshots and they are not the cause of your storage use.
To see only the dates, which you need for removing a specific snapshot, run:
tmutil listlocalsnapshotdates /You can also check whether Time Machine is set to back up automatically in System Settings → General → Time Machine. If it is turned off, macOS normally stops making hourly local snapshots, though update snapshots and snapshots from other apps can still exist.
Let macOS reclaim the space first
In most cases the right move is to let the system do its job:
- Connect your backup disk and choose Back Up Now from the Time Machine menu, or wait for the next scheduled backup. Once the data is safely on the backup disk, older local snapshots are no longer needed and macOS can remove them.
- Wait a day. Local snapshots older than about 24 hours are removed automatically.
- Restart if storage still looks wrong after a large deletion. Storage figures and purgeable space are recalculated.
- Install a pending macOS update and restart if prompted. An update in progress can hold its own snapshot until it completes.
If you need space right now, for example to install an update or copy a project, macOS frees purgeable snapshot space when an app asks for it. A large copy can start even when the free-space figure looks too small.
Remove snapshots yourself
If you understand what you are removing and still want to delete a snapshot, Apple's tmutil tool can do it. Removing a snapshot means you can no longer restore files from that point in time without the backup disk.
- List the dates with
tmutil listlocalsnapshotdates /. - Delete one snapshot by its date. You will be asked for your administrator password:
sudo tmutil deletelocalsnapshots 2026-11-07-093015Replace the date with one from your own list. Repeat for each snapshot you want to remove. Only remove snapshots whose names start with com.apple.TimeMachine this way. Snapshots made by other backup apps should be managed in that app, which knows whether it still needs them.
There is also a command that asks macOS to thin snapshots until a target amount of space is free. It is the closest thing to the automatic behaviour, and it only removes what macOS considers removable:
sudo tmutil thinlocalsnapshots / 21474836480 4The number is the space to free in bytes (here 20 GB) and the last value is the urgency, from 1 to 4. Avoid turning Time Machine off just to get rid of snapshots. You lose hourly protection, and turning it back on starts the cycle again.
| Situation | Best action | Trade-off |
|---|---|---|
| Storage looks high after deleting big files | Wait or back up, then check again | None; macOS reclaims the space on its own. |
| An install needs space now | Start it; macOS frees purgeable space | Usually none. |
| A specific old snapshot is not needed | sudo tmutil deletelocalsnapshots | That restore point is gone. |
| Snapshots from another backup app | Manage them in that app | Removing them outside the app can confuse it. |
| No snapshots listed | Look elsewhere | Snapshots are not your problem. |
Example: the deleted video that did not free space
A video editor exported a 60 GB render, checked it, and deleted it to make room. Finder showed it gone and the Trash was empty, yet available space barely moved and System Data had grown. tmutil listlocalsnapshots / listed six hourly snapshots taken while the render existed. The editor connected the backup drive and let Time Machine finish. A few hours later the older snapshots had been thinned and the 60 GB was available again, without any manual deletion.
Questions about local snapshots
Are local snapshots the same as my Time Machine backup?
No. Your backup is on a separate disk. Local snapshots are a short-term safety net on the startup disk itself and disappear after about a day.
Can I turn local snapshots off?
Turning off automatic Time Machine backups stops hourly local snapshots on current macOS versions. It also stops your backups, so it is rarely a good trade. Update snapshots and other apps' snapshots are not affected.
Is deleting a snapshot dangerous for my Mac?
It does not damage macOS or your files. You only lose the ability to restore from that moment without your backup disk.
Why does tmutil say the operation is not permitted?
Deleting snapshots needs administrator rights. Run the command with sudo. Listing snapshots does not need it.
Do snapshots explain all of my System Data?
Usually not. They are one contributor among many. See the System Data guide for the others, including browser leftover copies and large app data folders.
What MacMonitor shows
MacMonitor's System Data scan lists Time Machine local snapshots under Managed by macOS, with how many exist, so you can see whether they are part of the picture. It does not delete them: macOS manages them well, and removing restore points is a decision best made deliberately with the commands above.