If you have ever opened About This Mac, noticed your disk is nearly full, then watched the bar shrink after a reboot without deleting anything, you have encountered APFS local snapshots eating disk space. These snapshots are created automatically by Time Machine and macOS, they live inside what Apple calls "purgeable" storage, and they are invisible to most disk-usage tools. This post explains exactly what they are, why they grow so large, and what you can safely do about them.
What Are APFS Snapshots?
APFS (Apple File System), introduced with macOS High Sierra and standard on every Mac since, has a built-in snapshots feature. A snapshot is a frozen, read-only point-in-time image of your entire volume. Because APFS uses copy-on-write internally, a new snapshot takes almost no space at the moment it is created. Space is only consumed as files change — the old data is retained in the snapshot while the new data is written elsewhere on disk.
This is different from a traditional backup: a snapshot is not a separate copy of every file. It is a lightweight record of what the filesystem looked like at a specific moment, storing only the differences from the current state as time goes on.
How Time Machine Creates Local Snapshots
Starting with macOS Big Sur (and refined through Monterey, Ventura, Sonoma, and Sequoia), Time Machine takes a local snapshot of your startup volume once per hour, even when your backup drive is not connected. When the drive is connected, Time Machine uses these local snapshots as the source for its backup, then discards them. When you are away from your backup drive for days — traveling with a laptop, for example — hourly snapshots accumulate.
You can see every snapshot currently on your Mac with one Terminal command:
tmutil listlocalsnapshots /The output lists snapshot names like com.apple.TimeMachine.2025-11-14-083201. To see their sizes:
tmutil listlocalsnapshotdates / | tail -n +2 | while read d; do
tmutil localsnapshot / "$d" 2>/dev/null
doneA more direct way to inspect sizes is:
du -sh /.MobileBackups 2>/dev/null || echo "Not mounted separately"On most Macs running macOS Monterey or later, local snapshot data does not appear at /.MobileBackups as a separate mount point. Instead it is accounted for within the APFS container itself, which is why Finder and most third-party tools report it as free or purgeable space rather than used space.
Why Snapshots Appear in "Purgeable" Space
Apple's storage model classifies disk space into three buckets:
- Used — files you own and that apps report normally.
- Purgeable — data macOS is willing to delete automatically when you need room, including local snapshots, cached iCloud files already uploaded, and Optimized Storage items.
- Available — genuinely free space.
The Storage tab in System Information (or System Settings → General → Storage) adds Available and Purgeable together and shows the sum as free space. This is intentional: macOS will reclaim snapshot space on demand when an app requests a large allocation. In theory you should never run out of room because of snapshots alone.
In practice, some apps query free space directly from the filesystem without asking macOS to purge first. They see a small number, report a low-disk warning, and the user has no idea why. That is the scenario most people are trying to solve.
How Large Can Local Snapshots Get?
There is no fixed cap. Apple's documentation says macOS will not let local snapshots consume more than a certain portion of your disk, but the actual threshold depends on how much free space you have. On a 256 GB Mac that is reasonably full, it is common to see 10–30 GB sitting in snapshots. On a 1 TB disk with plenty of room and a week away from a backup drive, snapshots can grow larger.
The growth is proportional to how much your files are changing. Heavy work in Final Cut Pro, Xcode, or any tool that writes large files frequently will cause older snapshot versions to accumulate more delta data.
How to Check and Reclaim Snapshot Space
Option 1: Let macOS Handle It
If you simply connect your Time Machine backup drive and let a backup complete, macOS will automatically remove the local snapshots that have been backed up. This is the safest path — no manual steps, no risk.
Option 2: Delete Snapshots Manually with Terminal
If you do not have a Time Machine drive, or you want to reclaim space immediately, you can delete snapshots by date:
- List all snapshots:
tmutil listlocalsnapshots / - Copy a snapshot name from the output, for example
com.apple.TimeMachine.2025-11-10-083000. - Delete it:
(use only the date-time portion, not the full name).tmutil deletelocalsnapshots 2025-11-10-083000 - Repeat for each snapshot you want to remove.
To delete all local snapshots at once:
for snap in $(tmutil listlocalsnapshotdates / | grep -E '^[0-9]'); do
tmutil deletelocalsnapshots "$snap"
doneIs this safe? Yes, with a caveat. Deleting local snapshots does not affect your full Time Machine backup on an external drive or Time Capsule — those remain intact. However, if your Mac is your only backup (no external drive, no Time Machine destination configured), deleting local snapshots removes your only point-in-time recovery option. Do not delete them if they are your sole safety net.
Option 3: Disable Time Machine Temporarily
Disabling Time Machine stops new local snapshots from being created, but it does not delete existing ones. It is rarely the right move unless you are intentionally opting out of backups.
How Disk Tools Usually Miss This
Most disk-usage apps — including the built-in Storage view — either roll snapshot space into "purgeable" or ignore it entirely. That means you can scan your Mac, account for every user-visible file, and still have 20 GB unexplained.
Crumb surfaces this category explicitly. When you run a scan, the System Data breakdown includes purgeable space with a clear label, so you can see whether snapshots are a meaningful contributor on your machine rather than guessing. If you want to explore further, the Visualize tab shows the whole-Mac disk map including categories that standard tools hide. You can download Crumb and run a free scan without any account or subscription.
Comparison: Ways to Reclaim Snapshot Space
| Method | Reclaims space? | Risk level | Notes |
|---|---|---|---|
| Complete a Time Machine backup | Yes (gradual) | None | Safest; requires backup drive |
tmutil deletelocalsnapshots |
Yes (immediate) | Low* | *Only risky if snapshots are your sole backup |
| Wait for macOS auto-purge | Yes (on demand) | None | Happens when an app requests space; not instant |
| Disable Time Machine | No | Low | Stops new snapshots; does not remove old ones |
| Restart Mac | Sometimes | None | macOS may purge snapshots during shutdown/boot |
Key Takeaways
- APFS local snapshots are created hourly by Time Machine and grow as your files change.
- They live in "purgeable" space, so macOS counts them as available in most views.
- Connecting your Time Machine drive and completing a backup is always the cleanest solution.
- Manual deletion with
tmutil deletelocalsnapshotsis safe as long as you have a real backup elsewhere. - Most disk-scanning tools do not surface snapshot size clearly — look for apps that break out purgeable categories explicitly.
Understanding where your disk space actually goes is the first step to managing it well. Local snapshots are not a bug — they are a genuinely useful safety feature — but they deserve a visible accounting, not a hidden line in a "purgeable" catch-all.