Time Machine Is Using All My Disk Space on macOS Sequoia: Why It Happens and How to Fix It (2026)

If your Mac's storage bar shows gigabytes — sometimes dozens of them — consumed by something vague like "System Data" or "Backups," and you're certain you back up to an external drive, you've stumbled onto one of macOS's most misunderstood behaviors. Time Machine using all my disk space is a common complaint that traces to a single root cause: local snapshots stored directly on your internal SSD, completely separate from whatever is on your external backup disk.

Why Time Machine Takes Up Space on Your Internal Disk

When you set up Time Machine to back up to an external drive or NAS, macOS also quietly creates local snapshots on your startup volume. These hourly snapshots live inside an APFS snapshot layer — not as ordinary files you can browse — and are designed to let you recover deleted files even when your external drive isn't connected.

This is intentional and, most of the time, harmless. APFS marks snapshot space as purgeable, meaning macOS is supposed to delete old snapshots automatically when your disk fills up. In practice, that purging can lag, stall after a macOS update, or simply not keep pace if you generate a lot of data quickly. The result: Time Machine eating disk space on the very drive you thought it was leaving alone.

Local Snapshots vs. External Backups: The Key Difference

Step 1: Verify That Snapshots Are the Culprit

Before deleting anything, confirm that local snapshots are actually consuming significant space. Open Terminal and run:

tmutil listlocalsnapshots /

You'll see output like:

com.apple.TimeMachine.2026-05-30-083012
com.apple.TimeMachine.2026-05-30-093012
com.apple.TimeMachine.2026-05-30-103012
...

Each line is a snapshot. To see how much space all snapshots together are consuming, run:

tmutil listlocalsnapshotdates / | tail -n +2 | while read d; do tmutil listlocalsnapshots / | grep "$d"; done

For a quicker size estimate on macOS Ventura and later:

du -sh /.MobileBackups 2>/dev/null || echo "Path not directly accessible — use tmutil"

The most reliable method is to open System Settings → General → Storage and look at the "System Data" or "Backups" segment. If it's large and growing, local snapshots are the most likely explanation.

Alternatively, Crumb's Visualize tab runs a whole-Mac audit that surfaces snapshot and backup space in plain language alongside your largest files and folders — useful if you'd rather not interpret Terminal output.

Step 2: Understand What Is Safe to Delete

Local Time Machine snapshots are generally safe to delete because:

• Your primary backup still exists on the external drive.
• macOS can recreate local snapshots the next time Time Machine runs.
• Deleting them does not affect files currently on your disk — only the ability to roll back to a past version while offline.

Be aware of the trade-off: If you delete all local snapshots and your external drive is unavailable, you lose the ability to recover individual files from the past few hours or days until Time Machine runs again.

Step 3: Delete Local Snapshots

Option A — Delete a Specific Snapshot

Copy a snapshot name from the tmutil listlocalsnapshots output and run:

sudo tmutil deletelocalsnapshots 2026-05-30-083012

Replace the date string with the one you copied. You'll be prompted for your password.

Option B — Delete All Local Snapshots at Once

This removes every local snapshot from your startup volume:

tmutil listlocalsnapshots / | grep "com.apple.TimeMachine" | while read snap; do
  sudo tmutil deletelocalsnapshots "${snap##*.TimeMachine.}"
done

On some macOS versions a simpler loop works:

for snap in $(tmutil listlocalsnapshots / | awk -F. '{print $NF}'); do
  sudo tmutil deletelocalsnapshots "$snap"
done

After running either command, wait a minute and then check System Settings → Storage again. The bar should shrink noticeably.

Option C — Temporarily Disable Local Snapshots

If snapshots keep rebuilding faster than you'd like, you can turn off local snapshot creation without disabling Time Machine entirely:

sudo tmutil disablelocal

To re-enable later:

sudo tmutil enablelocal

Note: disablelocal is available on macOS Monterey through Sequoia. On macOS 26 (when released) the command surface may change — check man tmutil for your current system.

Step 4: Handle Other Causes of a Full Disk

If your disk is still tight after clearing snapshots, the culprit may be elsewhere. Common offenders on macOS include:

• ~/Library/Caches — Application caches that grow unbounded over time.
• /private/var/folders — Temporary files and derived data from Xcode or other tools.
• ~/Library/Application Support — Databases, offline content, and abandoned app data from apps you no longer use.
• iOS device backups at ~/Library/Application Support/MobileSync/Backup — These can be several gigabytes each.
• Large downloads, duplicate files, or old disk images (.dmg) in your Downloads folder.

Working through these manually takes time. If you want a faster survey, download Crumb and run the Visualize audit — it maps your entire disk and highlights the largest items and leftover folders from uninstalled apps, so you can decide what to clear with full context rather than guessing.

Preventing the Problem Going Forward

• Check Storage regularly. System Settings → General → Storage gives a quick overview. A sudden jump in "System Data" often signals snapshot accumulation.
• Keep your external drive connected more often. When Time Machine can reach its backup destination frequently, it has less reason to accumulate large local snapshots.
• Don't rely solely on macOS's auto-purge. The system will eventually reclaim purgeable space, but "eventually" can mean several hours or longer when a large file copy triggers the threshold.
• Prune iOS backups and Xcode simulators. These are not related to Time Machine but are common surprise consumers. Xcode's simulator runtimes can be removed from Xcode → Settings → Platforms.

A Note on Safety

Deleting local Time Machine snapshots is low-risk as long as your external Time Machine backup is current and intact. Before running any Terminal command, verify that your external backup has completed at least one recent successful backup — check System Settings → General → Time Machine for the "Last backup" timestamp. If the last backup was days ago or shows an error, fix that first before deleting local snapshots.

Cache cleaning is also generally safe, but deleting files from directories you don't recognize — especially outside your home folder — carries more risk. When in doubt, use a tool or command that specifically targets known-safe locations rather than broad recursive deletes.

Summary

Time Machine full disk surprises almost always come down to local APFS snapshots piling up on your internal SSD — not a problem with your external backup drive. The fix is straightforward: list your snapshots with tmutil listlocalsnapshots, delete them with tmutil deletelocalsnapshots, and optionally disable local snapshots if you want to prevent them from accumulating again. If other large items are still consuming space after that, a disk visualization tool helps you find them without guesswork.