What a local snapshot is
When Time Machine backs up automatically, your Mac also takes local snapshots: read-only, point-in-time copies of your startup disk, stored on that same disk. Apple describes the schedule like this: Time Machine saves a snapshot roughly every hour and keeps it for 24 hours, plus one extra snapshot of your last successful backup, which stays until the space is needed.
Snapshots are what let you open Time Machine on a train, without your backup disk, and still get back a file you deleted this morning.
They are a feature of APFS, the file system every current Mac uses. A snapshot does not copy your files. It records which blocks on the disk belonged to your files at that moment, and tells APFS not to reuse them.
Why they take up space
Right after it is taken, a snapshot uses almost no space, because it shares every block with your live files. It grows only as your files change:
- You delete a file. The file disappears from Finder, but its blocks still belong to the snapshot. The space comes back only when every snapshot that contains the file has expired.
- You edit or replace a file. The old version stays in the snapshot, the new version takes new space.
- A large download comes and goes. A 40 GB virtual machine image you downloaded and deleted in the same afternoon can live on in the snapshots for a day.
This is the most common reason people see “I deleted 50 GB and nothing changed”. The space is not lost. It is waiting for the snapshot to expire.
Do snapshots reduce your free space
In practice, mostly no. macOS marks local snapshots as purgeable and counts their space as available. When an app needs room and free space runs low, Time Machine deletes snapshots, oldest first, without asking. Apple also says snapshots are stored only on disks that have plenty of free space.
Where they can get in the way is with tools that check only the space
that is free right now, such as some installers, disk images and the
df command. For the full picture, see
Purgeable space on macOS explained.
How to see your local snapshots
Open Terminal and list the snapshots on your startup disk:
~ % tmutil listlocalsnapshots / Snapshots for disk /: com.apple.TimeMachine.2026-10-29-215507.local com.apple.TimeMachine.2026-10-29-225520.local com.apple.TimeMachine.2026-10-29-235517.local ~ % tmutil listlocalsnapshotdates / Snapshot dates for disk /: 2026-10-29-215507 2026-10-29-225520 2026-10-29-235517
On a Mac that is backing up normally, expect up to about two dozen snapshots covering the last day. One older snapshot is usually the one from your last successful backup. If its date is days or weeks ago, Time Machine has not finished a backup since then.
Other backup apps can take APFS snapshots too. To see every snapshot
on your data volume, including those, use diskutil:
~ % diskutil apfs listSnapshots /System/Volumes/Data Snapshots for disk3s1 (3 found) | +-- 33B26E27-73DC-40A8-93AE-75DC5A1348C6 | Name: com.apple.TimeMachine.2026-10-29-215507.local | Purgeable: Yes
Purgeable: Yes means macOS can delete that snapshot on its own when
it needs the space. Snapshots that are not purgeable belong to another
app and are that app’s responsibility.
macOS does not show how much space each snapshot holds in an easy
place. The total is part of the purgeable figure, and the difference
between df and Finder’s available space gives you a rough idea.
How to remove local snapshots
You rarely need to. When you do, for example before a large install or right after deleting big files, pick the gentlest option that does the job. None of these touch the backups on your Time Machine disk.
Let Time Machine finish a backup
Connect your backup disk (or make sure your network backup is reachable), then choose Back Up Now from the Time Machine menu in the menu bar, or Control-click the backup disk in Time Machine settings and choose Back Up Now. Once a backup completes, older snapshots become redundant and macOS cleans them up over time.
Turn automatic backups off briefly
This is Apple’s own method. Open System Settings, choose General, then Time Machine, click Options and set the backup frequency to Manually. Wait a few minutes for local snapshots to be deleted, then set it back to automatic. While it is off, your Mac takes no new backups, so do not forget the second step.
Thin snapshots from Terminal
thinlocalsnapshots asks Time Machine to reclaim a given amount of
space (in bytes) at an urgency from 1 to 4. It removes as many
snapshots as needed, oldest first:
# reclaim up to 100 GB at the highest urgency ~ % tmutil thinlocalsnapshots / 100000000000 4
Delete one snapshot
To remove a specific snapshot, pass its date as shown by
listlocalsnapshotdates. macOS may ask for your administrator
password:
~ % sudo tmutil deletelocalsnapshots 2026-10-29-215507Should you turn local snapshots off
No. There is no separate switch for them: local snapshots come with automatic Time Machine backups, and turning those off permanently means no automatic backups either. The space snapshots use is reclaimed on its own when you need it, so the trade-off rarely favors switching off.
If snapshots keep piling up, fix the cause instead. The usual ones are a backup disk that is never connected, a network backup that fails, or a backup that never finishes because the backup disk is full. Time Machine settings shows the date of the latest backup and any error.
Why the numbers keep changing
A new snapshot appears every hour and the oldest expires, so the purgeable space on a Mac with Time Machine moves all day. That is normal. It is worth a closer look only when very old snapshots remain, or when free space stays low after a completed backup and a restart.
