User level: Level 1 (4 points)My Time Machine says it has not backed up for 19 days. The external hard drive is plugged in and properly operating. It's a 5Tb disk with 1 Tb available. When I look at [external hard drive] > backups.backupdb > MacBook Pro (4) > it shows that the backup is "in progress", Calulating Size. It never gets out of that mode. What's going on?
MacOS: Tahoe 26.3.1, 1 Tb hard drive, 454 Gb available. Any ideas?
Posted on Sep 23, 2026 3:07 PM
User level: Level 6 (12,236 points)Sep 26, 2026 6:24 PM in response to JoeFlower
The “Calculating Size” you see in Finder isn’t necessarily Time Machine’s status. Finder may simply be trying to calculate the size of that incomplete backup.
Since Time Machine hasn’t completed a backup in 19 days, I’d stop the current backup from System Settings > General > Time Machine, restart the Mac, then try Back Up Now again. Don’t manually delete the “in progress” backup folder.
Apple notes that Time Machine can spend much longer preparing after an interrupted backup, a macOS update, or when it hasn’t backed up for several days.
→ If Time Machine remains in the preparing stage on Mac - Apple Support
If it stalls again, make sure the drive is connected directly to the Mac rather than through a hub. The next step I’d try is Disk Utility > First Aid on the backup drive. Apple specifically recommends First Aid when Time Machine can’t complete backups.
→ If you can't back up or restore your Mac using Time Machine – Apple Support
With about 1 TB still free on a 5 TB backup disk, I wouldn’t erase the drive or start over yet.
Originally posted at discussions.apple.com/thread/256363742