Quick answer
If Time Machine is not backing up, first check that the external disk is properly connected and has enough space. Then go to System Settings > General > Time Machine to check the status and start a manual backup. If it still does not work, remove and re-add the disk.
How to recognize the problem
- Time Machine icon in the menu bar shows an exclamation mark or "Backup Failed"
- The last backup is several days or weeks old
- The backup starts but stops without an error message
- The backup disk is not visible in Finder or Disk Utility
- The message "Time Machine could not complete the backup"
Most common causes
External disk is not properly connected
The cable, port, or disk power supply can interrupt the connection during operation. Check whether the disk appears in Finder and in Disk Utility.
Not enough space on the backup disk
Time Machine requires free space for new versions of files. If the disk is full or nearly full, Time Machine may not be able to create a new backup.
Corrupted file system on the backup disk
Errors in the disk structure can prevent writing. Disk Utility can detect and repair such problems.
Network problems with wireless backup
If you use a Time Capsule or network disk, an unstable Wi-Fi connection interrupts the transfer. Check the connection and possibly switch to Ethernet.
Incorrect settings or a stuck process
Sometimes the Time Machine process gets stuck or the disk settings are incorrect. Removing and re-adding the disk solves the problem.
Step-by-step fix
- 1
Check the physical connection and disk power
Unplug and replug the disk cable, preferably into another USB port. If the disk has an external power supply, check that it is turned on. In Finder, check whether the disk is visible in the sidebar.
- 2
Check the status in Time Machine settings
Open
System Settings>General>Time Machine. In the "Backups" section, check whether the disk is shown and whether "Last backup" displays a time. If it says "Backup Failed", click the notification or open the details if available. - 3
Check free space on the backup disk
In Finder, select the backup disk and press
Command + Ito see information. If the space is almost full, connect a larger disk or, if you do not need older backups, delete them with caution (first check that you have important data elsewhere). Time Machine automatically deletes the oldest backups when the disk needs space, but this does not help if free space is critically low. - 4
Start a manual backup
In the menu bar, click the Time Machine icon and choose
Back Up Now. If the icon is not visible, inSystem Settings>Control Centerenable showing Time Machine in the menu bar. Watch for any error message. - 5
Check the disk using Disk Utility
Open
Disk Utility(inApplications>Utilities). Select the backup disk in the sidebar, clickFirst Aid, and run the check. If Disk Utility finds errors, try to repair them. If it cannot, you may need to format the disk (which erases all data and Time Machine backup history). Before formatting, back up important data to another disk. - 6
Remove and re-add the backup disk
In
System Settings>General>Time Machine, click the backup disk, then click-to remove it. Then click+again and add the same disk. Time Machine will continue to use existing backups if they are preserved. - 7
Check the network if you use a network disk
If the backup goes to a network disk (e.g., Time Capsule or NAS), check that the Mac is connected to the same network. Switch to Ethernet if possible. In
System Settings>Network, check the connection status and possibly restart the router. - 8
Restart the Mac and start the backup again
Sometimes a restart is enough to free stuck processes. After restarting, start
Back Up Nowagain from the Time Machine menu. Wait for the backup to complete without interruption.
If nothing helps: advanced options
If all steps have been tried and Time Machine still does not work, restart the Mac and turn the backup disk off and on again, and check whether macOS is up to date. Do not manually delete files in the backup structure (on older HFS+ disks it is Backups.backupdb, and on APFS disks the structure is different) because you can damage the backups. If an incomplete backup is stuck, contact IT support or, as a last option, format the backup disk, but only after you have backed up important data to another disk. For business users, consider a centralized backup solution.
How to prevent it
- Regularly check whether Time Machine is making backups (once a week)
- Keep the backup disk in a stable place and use a quality cable
- Ensure enough free space on the backup disk
- Update macOS regularly for backup-related bug fixes
When to call a professional
If you have tried all the steps and Time Machine still does not work, or if you suspect a hardware failure of the disk, contact IT support. Also, if your data is extremely important, do not risk formatting the disk without professional help.
IT infrastructure maintenance · Servers, networks, backup, security and helpdeskFAQ
Why doesn't Time Machine see my external disk?
Check whether the disk is formatted as APFS or Mac OS Extended (Journaled). If it is formatted as NTFS or exFAT, Time Machine will not use it. Also, check the cable and port.
Can I continue using existing backups after removing and re-adding the disk?
Yes, if the disk is not formatted and you preserve the folder structure. When you re-add the disk, Time Machine should recognize the existing backups and continue using them.
How often does Time Machine make backups?
Time Machine makes automatic backups every hour for the last 24 hours, daily backups for the last month, and weekly backups as long as there is space. You can also start a backup manually at any time.