Time Machine error: Unable to complete backup, fix now


  • Wait before trying again to see if the issue resolves on its own
  • Halt ongoing backup processes and address disk or file system issues
  • Verify external hard drive compatibility with Time Machine
  • Exclude oversized and unnecessary files, prevent Spotlight indexing, eliminate unneeded backups, restart and clean backup disk, troubleshoot with logs and cable checks, update system, and adjust sleep settings

Having trouble completing your Time Machine backup? Let’s address the issue and fix it promptly.

Wait Before Trying Again

Before attempting to backup again, wait a few moments to see if the issue resolves on its own. Sometimes the error may be temporary and can be fixed with a little patience.

If the problem persists, check your internet connection to ensure that it is stable and working properly. A poor connection can cause interruptions during the backup process.

Additionally, restart your computer to refresh the system and potentially resolve any underlying issues that may be causing the backup error.

If the error continues to occur, check for software updates on your Mac to make sure you are running the latest version of the operating system, which may contain bug fixes that address the backup problem.

Waiting before trying again can sometimes save you time and effort, as the issue may resolve itself without any further action needed.

Halt Ongoing Backup Processes

To fix the “Time Machine error: Unable to complete backup” issue, the first step is to halt any ongoing backup processes. Open Time Machine from the menu bar or System Settings, then click on the Stop Backup option. This will pause the backup process and allow you to troubleshoot the problem.

Next, check if there are any issues with the disk partitioning or the file system of the drive where the backup is being stored. Use Disk Utility to repair any disk errors or inconsistencies that may be causing the backup to fail.

If the backup drive is formatted in a file system that is not supported by Time Machine (macOS), such as NTFS, consider reformatting it to HFS Plus or another compatible format.

After addressing any disk or file system issues, you can resume the backup process in Time Machine and monitor the progress. If the error persists, further troubleshooting may be necessary to identify the root cause and resolve the issue.

Verify External Hard Drive Compatibility

External hard drive compatibility list.

External Hard Drive Brand Model Compatibility
Seagate Backup Plus Slim Compatible
Western Digital My Passport Compatible
Samsung Portable SSD T5 Compatible
Toshiba Canvio Basics Compatible
LaCie Rugged Mini Compatible

Exclude Oversized, Unnecessary Files

Folder with oversized files

To fix the Time Machine error “Unable to complete backup,” start by excluding oversized and unnecessary files from the backup process. Open Finder and navigate to the files you want to exclude. Right-click on the file and select “Get Info” to check the file size. If the file is too large or unnecessary for backup, move it to a separate location or delete it. By removing these files, you can free up space and ensure a successful backup process.

Prevent Spotlight Indexing Backup

To prevent Spotlight indexing from interfering with your Time Machine backup, you can exclude certain folders from being indexed.

To do this, open System Preferences and go to Spotlight. Then, go to the Privacy tab and click on the + symbol to add the folders you want to exclude from indexing.

You can also exclude external drives from being indexed by Spotlight to avoid any potential conflicts with Time Machine backups.

By taking these steps, you can ensure that Spotlight indexing does not interfere with the completion of your Time Machine backups.

Eliminate Unneeded Backups and Snapshots

  • Open Time Machine on your Mac
    • Click on the Time Machine icon in the menu bar and select “Enter Time Machine”
  • Delete old backups
    • Scroll through the backups and select the ones that are no longer needed
    • Right-click on the selected backups and choose “Delete Backup”
  • Remove unnecessary snapshots
    • Open Terminal on your Mac
    • Type tmutil listlocalsnapshots / and press Enter
    • Identify the snapshots that are no longer needed
    • Type sudo tmutil deletelocalsnapshots [snapshot name] and press Enter to delete the snapshot

Restart and Clean Backup Disk

To restart and clean your backup disk, first, ensure that your Time Machine backup is not in progress. Next, restart your Mac to refresh the system. Once your Mac has rebooted, open Finder and navigate to your backup disk.

Then, right-click on the disk icon and select the option to Eject. After the disk has been ejected, disconnect it from your Mac and reconnect it. This will help to refresh the connection between your Mac and the backup disk.

Next, open Disk Utility from your System Settings and select your backup disk. From here, you can choose the option to Erase the disk, which will clear any existing data and start fresh.

Once the disk has been erased, go back to Time Machine settings and select the newly cleaned disk as your backup destination. This should resolve any issues you were experiencing with completing your backup.

Troubleshoot with Logs and Cable Checks

To troubleshoot the “Time Machine error: Unable to complete backup” issue, you can start by checking the logs and cables. First, open Console and look for any error messages related to Time Machine backup failures.

Next, inspect the cables connecting your external drive to your Mac. Make sure they are securely plugged in and not damaged. You can also try using a different cable to rule out any connectivity issues.

If the logs show any disk partitioning or file system errors, you may need to repair the disk using Disk Utility. This can help resolve any issues with the disk’s File Allocation Table or partition structure.

Additionally, make sure that your external drive is formatted correctly for Time Machine backups. MacOS requires drives to be formatted with HFS Plus, not NTFS or other file systems. You can check and reformat the drive using Disk Utility if needed.

If you are using MacOS Big Sur, you may encounter compatibility issues with older drives formatted with the GUID Partition Table. Consider reformatting the drive with the newer APFS file system.

Update System and Adjust Sleep Settings

To fix the Time Machine error and complete the backup successfully, update your system and adjust the sleep settings on your computer. First, update your macOS to the latest version to ensure compatibility with Time Machine. Next, adjust your sleep settings to prevent your computer from going to sleep during the backup process.

To update your macOS, go to the Apple menu and select “System Preferences.” Then, click on “Software Update” and follow the prompts to install any available updates. This will ensure that your system is up to date and ready to complete the Time Machine backup.

To adjust your sleep settings, go to the Apple menu and select “System Preferences.” Then, click on “Energy Saver” and adjust the sleep settings to a longer duration or disable sleep mode entirely while the backup is in progress. This will prevent interruptions to the backup process and help ensure that it can be completed successfully.

By updating your system and adjusting the sleep settings, you can fix the Time Machine error and complete the backup without any issues.


Why is my Time Machine backup not completing?

Your Time Machine backup may not be completing because your backup disk may not be plugged in, turned on, or securely connected to your Mac. Additionally, if your backup disk is on a network, ensure that both the disk and your Mac are connected to the network properly. Problems with the network connection can also cause issues with completing the backup.

Why won’t Time Machine let me go back?

Time Machine won’t let you go back if the restore button is greyed out, possibly due to issues such as a formatted backup HDD, incomplete backup, or corrupted backup.

How do I force a full backup on Time Machine?

To force a full backup on Time Machine, you would need to erase the Time Machine drive and start the backup process again from scratch. Incremental backups will cover everything that the initial backup did not, but the backup will always be smaller than the source due to logs, caches, and non-essential files not being included.

How do I reset a Time Machine backup?

To reset a Time Machine backup on a Mac, you can go to System Preferences > Time Machine, select the disk for backup, click “Select Disk”, and then “Remove Disk”. After that, you can reselect the disk to start a new backup session.