Time Machine .inProgress files: when to leave them and when to delete them

When a backup is interrupted, by sleep, a disconnected drive or a cancel, Time Machine leaves the partial backup on the drive as an item ending in .inProgress, named with the date it started. It does not appear when you browse backups, so it looks like lost space.

Usually, leave it

On the next backup Time Machine picks up the partial one and carries on, so it does not copy those files twice. Deleting it just makes the next backup slower. Let one backup finish with the drive connected and the Mac awake, and it disappears by itself.

When to delete it

Delete it when the partial backup is something you never meant to back up, such as a huge virtual machine or a video library you have since excluded, or when backups keep failing at the same point. Exclude the large item first, in System Settings, General, Time Machine, Options, so it is not copied again.

# Find partial backups on a connected backup drive (replace the name)
find "/Volumes/<Backup drive>" -maxdepth 3 \( -name '*.inProgress' -o -name '*.interrupted' \) 2>/dev/null

1. Turn off automatic backups in Time Machine settings, or run tmutil stopbackup if one is running.
2. In Finder, open the backup drive. On older backup drives the item is in Backups.backupdb, inside the folder named after your Mac.
3. Drag the .inProgress item to the Trash, then empty the Trash.
4. Turn backups back on and let one complete.

Related: Time Machine backup drive is full and Time Machine using your internal disk.