APFS local snapshot
Also known as: Time Machine local snapshot, local snapshot Mac, APFS snapshot
An APFS local snapshot is a point-in-time copy of your startup disk that Time Machine stores locally so you can restore recent changes even without the backup drive attached. The snapshots temporarily occupy disk space and macOS deletes them automatically when space is needed.
- Hourly snapshots kept ~24 hours on APFS disks
- Counts toward used space, usually under System Data
- Deleted automatically when space is needed
How local snapshots work
When Back Up Automatically is on, Time Machine saves a snapshot of your startup disk roughly every hour and keeps it for 24 hours, plus one snapshot of your last successful backup until space is needed. On macOS High Sierra and later, an extra snapshot is saved before any macOS update.
Snapshots are stored only on APFS disks. They record what changed rather than full copies, but the space they hold still counts toward used storage and often shows up under System Data.
Why they fill the disk — and clear on their own
Because snapshots accumulate between backups, they can occupy a noticeable chunk of the disk. Time Machine removes them automatically when space runs low or once they pass 24 hours old, so this space is purgeable rather than permanently lost.
You rarely need to delete snapshots by hand. Letting the disk fill triggers their removal, and connecting the backup drive lets Time Machine commit and thin them normally.