Retention: how long backups are kept
Three numbers in one sentence: keep N sets, a new full after N runs, delete sets older than N days. And the chain rule that keeps every set restorable.
On this page
Every run adds a set. Retention removes old sets so the destination does not fill up. It is set as one sentence on the wizard's Settings step and applied at the end of each run.
The sentence#
Keep 5 sets, start a new full after 7 runs, delete sets older than 90 days.
| Number | Meaning | Default |
|---|---|---|
| Keep N sets | the job keeps its newest N sets | 5 |
| New full after N runs | for incremental and differential jobs: after N runs the next one is a full, which starts a new chain | 7 |
| Delete sets older than N days | sets older than this go after a run | 90 |
Each field takes 1 to 999, or empty for never. Under the fields the app says what the numbers add up to, for example Sets older than 90 days are deleted after a run.
The chain rule#
An incremental or differential set is useless without the full it builds on, so retention removes whole chains only. A chain goes when every set in it is past either limit, and the newest chain always stays. For a while the drive can hold more sets than the number says. It never holds a set you cannot restore.
A file the latest run could not read (open in another program, a OneDrive file that would not download) keeps its last backed-up copy in the new backup, and the report says so under the file: Its last backed-up copy, from 9 Nov 2026, 15:00, is kept in this backup. The older backup then goes when the numbers say. Only when those copies would take more than half the destination's free space does the older backup stay instead, and the report says which and why.
What the report shows#
The Retention line on the report's Destination card reads Deleted 2 old sets, freed 3.1 GB, or Nothing purged. The same card shows the sets on the destination.
Mirrors#
A mirror keeps exactly one copy; the previous one is removed once the new one is complete (each run moves the unchanged files' copies over from it and writes only what changed). The retention fields are replaced by a note on mirror jobs.
Free, Home and Pro#
On Free only Keep N sets can be set; the age limit and the new full every N runs are part of Home and Pro. An incremental job on Free therefore never starts a second full: its sets form one chain, none is removed, and the destination grows by what changes. The Settings step says The sets form one chain, so none is removed and the backup grows with your changes. To have old sets removed on Free, use Full for that job.
Deleting a backup yourself#
On the Restore page, the bin beside a backup deletes it. The app shows first what goes: the backup, and the later backups that build on it and could not be restored without it. Tick I understand that deleted backups can't be restored and click Delete. See Deleting a backup.
Choosing numbers#
| Job | Settings | Gives |
|---|---|---|
| Documents & Desktop, daily incremental | keep 30 sets, new full after 7, age never | about a month of daily points |
| Code & projects, every 4 hours, differential | keep 42 sets, new full after 6, age never | about a week, with a full every day |
| Design archive, weekly full | keep 4 sets | the last month |
| Everything, encrypted, weekly incremental | keep 8 sets, new full after 4 | about two months |
| A large archive (photos, video), daily incremental, all its history | every field empty | one full, then only the changes, kept for good |
On a large job, each new full writes the whole job again: a 1.4 TB job with start a new full after 7 runs and a daily schedule writes 1.4 TB a week. The Settings step says so: Each new full backup writes about 1.4 TB again. Leave start a new full after empty to keep one full backup and add only the changes.
Whichever limit a chain passes first removes it. An age limit shorter than the set count allows is the one that decides; a longer one never removes anything.
Tip
Retention only removes sets this job wrote. Another job's sets in the same folder are left alone.