To delete old Time Machine backups stored on your Mac's internal disk, thin the local snapshots with the tmutil command in Terminal — it's built for exactly this and never touches the backups saved on your external drive.
TL;DR
- Local snapshots are hourly backups macOS saves on the internal disk; they can grow to 50–100 GB.
- List them:
tmutil listlocalsnapshots /. - Free space fast:
tmutil thinlocalsnapshots / 10000000000 4(frees ~10 GB). - Delete one specific snapshot:
sudo tmutil deletelocalsnapshots 2025-10-15-142031. - This never affects backups on your external Time Machine drive.
Why does Time Machine use space when my backup drive is unplugged?
Local Time Machine snapshots are hourly point-in-time copies of changed files that macOS stores on your internal disk, so you can still restore recent edits even when the external backup drive isn't attached. macOS marks these snapshots as Purgeable and promises to delete them automatically when space runs low. In practice that cleanup often fires too late — a large app install or a partition operation fails because the system hasn't caught up. That's why they can quietly occupy 50–100 GB and show up as "System Data" or "Other."
How do I clear local snapshots with tmutil?
Terminal sounds intimidating, but tmutil is the official, supported tool for this cleanup.
- open Terminal (Applications › Utilities, or via Spotlight)
- list current snapshots:
tmutil listlocalsnapshots / - to free roughly 10 GB urgently:
tmutil thinlocalsnapshots / 10000000000 4 - to delete one specific snapshot:
sudo tmutil deletelocalsnapshots 2025-10-15-142031, then enter your password
The date in the last command must match one of the timestamps listed in step 2. The number in step 3 is the target free space in bytes (10000000000 ≈ 10 GB), and the trailing 4 is the urgency level.
What if the weight isn't snapshots?
If Terminal shows only a handful of snapshots but "System Data" is still huge, the weight lives elsewhere — usually app caches, Xcode derived data, or log files, not Time Machine. Check those before assuming snapshots are the culprit. Xcode's derived data alone routinely reaches tens of gigabytes on developer machines.
Is deleting local snapshots safe?
Yes. Thinning or deleting local snapshots with tmutil is safe: it only removes the temporary copies stored on your internal disk and never touches the full backups on your external Time Machine drive. Those external backups remain your real safety net. The only thing you lose is the ability to roll back very recent local edits without the external drive connected — a minor trade-off when you're out of space. tmutil is Apple's own utility, so you're not using a risky third-party hack.
FAQ
Why does Time Machine take up space on my Mac when the backup drive isn't connected?
macOS keeps hourly local snapshots of changed files on the internal disk so you can restore recent edits without the external drive. These are marked Purgeable but often aren't deleted in time, so they can grow to 50–100 GB and appear as System Data.
Does deleting local snapshots delete my Time Machine backups?
No. tmutil only removes the temporary local snapshots on your internal disk. The complete backups stored on your external Time Machine drive are untouched and remain fully restorable.
How do I free up space from Time Machine quickly?
Run tmutil thinlocalsnapshots / 10000000000 4 in Terminal to free about 10 GB of local snapshots at once. List them first with tmutil listlocalsnapshots /.
My System Data is still huge after clearing snapshots. What now?
If snapshots weren't the main culprit, the space is usually in app caches, Xcode derived data, or log files. Clear those next rather than expecting Time Machine to be the cause.
If clearing snapshots only dented the problem, the rest of your "System Data" is likely caches. Tackle them with mysterious System Data on Mac: how to safely clean the disk, how to clear Xcode cache and derived data, and how to clear Adobe Premiere / After Effects media cache. For a guided cleanup path, follow the clean up phone storage hub, and if your iPhone is filling up too, Cleanor finds duplicate photos and large videos on-device — scanned locally, nothing uploaded.