Time Machine Error 45
Apple macOS
Severity: ModerateWhat Does This Error Mean?
Time Machine Error 45 means the backup drive cannot be accessed or is not responding correctly. Your Mac tried to write a backup but the destination drive failed to cooperate. This is usually caused by a corrupted backup database, a bad USB/Thunderbolt connection, or a drive that is running out of space.
Affected Models
- MacBook Air
- MacBook Pro
- iMac
- Mac Mini
- Mac Studio
Common Causes
- The Time Machine backup database (called a sparsebundle) has become corrupted
- The backup drive is running out of space and cannot accept new data
- A loose or faulty USB or Thunderbolt cable connecting the backup drive
- The backup drive itself is starting to fail
- macOS permissions on the backup drive have become incorrect
How to Fix It
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Eject and reconnect the backup drive. Click the drive on your Desktop and press Command + E to eject it. Wait 10 seconds, then unplug and replug the cable. Try the backup again.
Sometimes a simple reconnection clears a temporary communication error between macOS and the drive.
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Check how much space is left on the backup drive. Open Finder, click on the drive, and look at the bottom of the window for available space. Time Machine needs free space to work.
Time Machine automatically deletes old backups to make room, but sometimes it gets stuck. If the drive is over 95% full, consider getting a larger drive.
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Delete and recreate the Time Machine backup. Open System Settings > General > Time Machine. Remove the current backup destination and add it back. Start a fresh backup.
Warning: this deletes your old backup history. Only do this if you are willing to start fresh.
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Run First Aid on the backup drive. Open Disk Utility (Applications > Utilities > Disk Utility). Select the backup drive on the left and click First Aid.
First Aid scans the drive for file system errors and repairs what it can. This often fixes the corrupted backup database.
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Try a different cable or USB port. Swap the cable connecting the drive to your Mac and use a different port. A faulty cable can cause intermittent read/write errors that trigger Error 45.
USB-C and Thunderbolt cables can look fine but have internal damage. Testing with a different cable costs nothing.
When to Call a Professional
If the backup drive makes clicking or grinding noises, it is physically failing. Do not try to fix it yourself — stop using it and take it to a data recovery specialist. Click noises mean the read/write head is damaged, which can cause permanent data loss.
Frequently Asked Questions
Will I lose my old backups if I start a new Time Machine backup?
Yes — if you delete the backup destination and start fresh, your old backup history is gone. You will not be able to restore files from those old backups. Only do this if you are okay starting fresh and your current Mac files are safe.
How big should my Time Machine drive be?
Apple recommends a backup drive that is at least twice the size of the data on your Mac. For example, if your Mac has 500 GB of data, use at least a 1 TB backup drive. Bigger is better — Time Machine keeps multiple versions of files over time.
Can I use Time Machine over Wi-Fi?
Yes — if you have an AirPort Time Capsule or a compatible NAS (network storage device). Wi-Fi backups are slower and more prone to errors than a direct cable connection. If you keep getting backup errors over Wi-Fi, try connecting the drive directly to your Mac with a cable.