Your Time Machine drive is full, and that is how it is meant to work
Time Machine fills the destination on purpose and thins old backups itself. When to intervene, how to delete backups properly, and when to start fresh.
A full Time Machine drive is usually not a problem. Time Machine keeps as much history as the destination allows and deletes the oldest backups when it needs room, which means a healthy backup drive sits at nearly full forever.
When it is genuinely a problem
- Backups are failing with a message about space, rather than quietly thinning.
- The oldest backup is recent, meaning history is being lost faster than you want.
- The drive is too small for the Mac it backs up, which is the underlying cause of both.
Check what is actually there
tmutil destinationinfo
tmutil listbackups 2>/dev/null | tail -10
df -h /Volumes/*listbackups shows how far your history reaches. If the oldest entry is a fortnight ago on a drive you have had for years, the drive is too small rather than misbehaving.
Deleting backups properly
sudo tmutil delete -d /Volumes/BackupDrive -t 2026-01-15-120000That removes one backup. Deleting backup folders in Finder is the version that goes wrong, because the structure uses hard links between backups and removing files by hand can leave the whole set inconsistent. On an APFS destination the backups are snapshots and Finder cannot meaningfully delete them at all.
How big a backup drive should be
| Mac data | Reasonable destination | Gives you |
|---|---|---|
| 500 GB used | 1 TB | Several months of history |
| 500 GB used | 2 TB | A year or more |
| 1 TB used | 2 TB minimum | Months, not years |
| Any size | Same size as the Mac | Barely one backup. Avoid |
Two to three times the data you are backing up is the rule that produces useful history. Equal size technically works and gives you almost no depth, which defeats the purpose of having history at all.
Excluding what does not need backing up
Virtual machines, downloaded media and build output all change constantly and are all replaceable, and excluding them in Time Machine settings buys history for everything that matters. That is the same reasoning as what is worth keeping on the Mac itself.
If the confusion is about space on the Mac rather than on the backup drive, how Time Machine uses the internal disk covers local snapshots, which is a different mechanism entirely.
Common questions
Is it normal for a Time Machine drive to be full?
Yes. Time Machine uses the whole destination and deletes the oldest backups when it needs space, so a healthy backup drive stays nearly full. It is only a problem when backups fail or history is shorter than you want.
How do I delete old Time Machine backups?
Use sudo tmutil delete -d with the destination and the backup timestamp. Deleting backup folders in Finder can corrupt the backup set, because backups share files through hard links.
How big should a Time Machine drive be?
Two to three times the data you are backing up, which gives months of useful history. A destination the same size as your data holds barely one backup and defeats the point of having history.
Why does Time Machine say there is not enough space?
Usually because the destination cannot thin far enough to fit the new backup, which means the drive is too small for the data. Excluding large replaceable files, or using a bigger drive, are the two real fixes.