Time Machine Backup Keeps Failing? Fixes That Work

Updated 7 November 2026 · Standard formula, shown below

If your Time Machine backup keeps failing, the most common causes are an incompatible or full backup drive, a corrupted local snapshot, or a permissions issue on the Mac itself. This guide walks you through the exact steps to diagnose and fix the problem, from simple restarts to rebuilding the backup database.

Why Time Machine Fails: The Usual Suspects

Time Machine is designed to be hands-off, but it depends on a few things going right. When one of those breaks, backups fail with little or no explanation. The main culprits are:

Backup drive not properly formatted – Time Machine requires Mac OS Extended (Journaled) or APFS. ExFAT or NTFS drives won’t work.
Insufficient free space – The backup drive needs at least as much free space as the data you’re backing up, ideally more.
Corrupted local snapshots – These temporary backups on your internal drive can conflict with the main backup.
Network issues – If backing up to a NAS or AirPort Time Capsule, a dropped connection mid-backup can leave the process stuck.
macOS permissions glitches – The backup daemon may lose access to certain folders.
Drive not ejected safely – Removing the drive during a backup can corrupt the backup structure.

First Steps: Restart and Reconnect

Before doing anything drastic, try the simplest fixes. They resolve a surprisingly large number of failures.

Restart your Mac. This clears any hung processes, including backupd (the Time Machine daemon).
If using an external drive, unplug it, wait 10 seconds, and plug it back in. Choose a different USB port if possible.
If backing up over Wi-Fi, move closer to the router or use an Ethernet cable temporarily to rule out signal issues.
Open Time Machine settings (System Settings > General > Time Machine) and turn the backup switch off, wait 30 seconds, then turn it back on. This often resets the schedule.

If the backup still fails, check the drive itself.

Check the Backup Drive’s Format and Health

Time Machine is picky about file systems. If you’re using a drive that was previously used on a Windows PC or a camera, it’s likely formatted as ExFAT or FAT32. Here’s how to check and fix it:

Open Disk Utility (Applications > Utilities).
Select your backup drive in the sidebar and look for the format listed under the drive name.
If it says ExFAT, MS-DOS (FAT), or NTFS, you must reformat it. Warning: This erases all data on the drive. If you have files on it, copy them elsewhere first.
Click Erase, choose Mac OS Extended (Journaled) or APFS, and give it a name. For macOS Catalina and later, APFS is the default and works well.

Also check the drive’s health. In Disk Utility, click First Aid on the backup drive. If it reports errors, run it again or consider replacing the drive. A failing drive will cause repeated failures.

Free Up Space on the Backup Drive

Time Machine needs room to work. Apple recommends the backup drive have at least as much free space as the amount of data you’re backing up. If your Mac has 500 GB of used storage, a 500 GB backup drive will fill up quickly because Time Machine keeps hourly, daily, and weekly snapshots.

When the drive is full, Time Machine deletes the oldest backups to make room. But if it can’t delete fast enough, or if the drive is completely full, it will fail. To fix this:

Delete old backups manually: In Time Machine, enter the backup timeline, browse to an old folder, and delete it. Or use the command line: tmutil listbackups to see them, then tmutil delete with the path.
Use a larger drive. A good rule of thumb is 2–3 times the size of your internal drive.
Exclude large folders you don’t need backed up (like a movies folder) in Time Machine settings.

Delete Corrupted Local Snapshots

macOS creates local snapshots on your internal drive when the backup drive isn’t connected. These are meant to be temporary, but they can become corrupted and interfere with the main backup. To clear them:

Open Terminal (Applications > Utilities).
Type tmutil listlocalsnapshots / and press Enter. You’ll see a list of snapshots.
Delete them all with sudo tmutil deletelocalsnapshots / (you’ll need your admin password).
Restart your Mac.

This doesn’t delete your actual backups, only the temporary local ones. After restarting, try the backup again.

Rebuild the Backup Database

If the backup still fails, the backup database on your drive may be corrupted. This can happen after a crash or improper ejection. Rebuilding it forces Time Machine to start fresh while keeping your existing backups.

In Terminal, run sudo tmutil disable to turn off Time Machine.
Run sudo tmutil enable to turn it back on.
If that doesn’t help, you may need to delete the .inProgress file on the backup drive. In Finder, press Cmd+Shift+. to show hidden files. Navigate to the backup drive and look for a folder named Backups.backupdb. Inside it, delete any file with .inProgress in the name.
If the problem persists, the last resort is to exclude the backup drive in Time Machine settings, then re-add it. This will force a new backup, but you’ll lose the backup history.

Network-Specific Fixes for NAS and Time Capsule

Backing up to a network drive adds complexity. Common issues include SMB protocol mismatches and the Mac going to sleep mid-backup. Try these:

In System Settings > General > Time Machine, click Options and add your Mac’s internal drive to the exclusion list, then remove it. This resets the network connection.
Ensure the NAS supports Time Machine over SMB. Some older NAS devices only support AFP, which newer macOS versions no longer support.
In Energy Saver settings, set Prevent automatic sleeping when the display is off for the duration of the backup.
If using a Time Capsule, update its firmware through AirPort Utility.

Frequently Asked Questions

Why does Time Machine say “The backup could not be completed”?

This generic message usually means the backup drive couldn’t be read or written. Check the drive’s format, free space, and connection. If it’s a network drive, try a wired connection. Also check the Console app for detailed error logs under “backupd”.

Can I use an external SSD for Time Machine?

Yes, SSDs work fine and are actually faster. Just make sure it’s formatted as Mac OS Extended (Journaled) or APFS. Note that SSDs have a limited write lifespan, but for typical home backups, that’s rarely a concern.

How do I see what’s actually causing the failure?

Open the Console app (Applications > Utilities), search for “backupd” in the search field, and look for error messages. The most useful entries are those with “Error” or “Failed” in the message. This will often tell you if it’s a disk space issue, a permissions problem, or something else.

Will deleting old backups free up space?

Yes. Time Machine automatically deletes the oldest backups when the drive is full, but you can also do it manually. In Time Machine, enter the timeline, select a backup from the past, and delete it. Or use the tmutil command in Terminal. Just be aware that you can’t delete individual files from a backup – only entire dated backups.

Is it safe to use the same drive for Time Machine and other files?

Technically yes, but it’s not recommended. Time Machine will use all available free space, and other files can interfere with the backup structure. It’s best to dedicate a drive exclusively to Time Machine.

Why does my backup take forever?

The first backup is always the longest because it copies everything. Subsequent backups only copy changes. If it’s still slow, check that your Mac isn’t sleeping, the drive is connected via a fast port (USB 3.0 or Thunderbolt), and that you don’t have huge files that change frequently (like virtual machines). Excluding those can speed things up.

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