Full and incremental backup schedule · user-entered sizes
Backup retention storage calculator
Estimate storage for full and incremental backups kept within a defined retention window. Use measured backup sizes and an explicit schedule; the result does not recommend a retention policy.
Model the storage occupied by a repeating full-and-incremental backup schedule over a chosen retention window. Enter sizes measured from your own backup system; the calculator does not choose a safe retention policy for you.
Enter all five values and calculate.
Schedule assumptions
- The newest full backup is today (day 0), and older full backups recur at the entered interval.
- Incrementals recur at the entered interval between full backups. The incremental interval must divide evenly into the full interval; a full backup replaces an incremental on the same day.
- The retention window includes backups with ages from day 0 up to, but not including, the entered number of days.
- Each retained full uses the entered full size; each retained incremental uses the entered average incremental size.
This is a capacity scenario, not a recommended retention period or a complete recovery-chain planner. It excludes metadata, compression changes, deduplication, temporary workspace, growth, replicas, and provider overhead. Confirm how your software prunes backup chains and test restores before relying on a retention setting.
Sources
- CISA, Data Backup Options — discusses backup options and the 3-2-1 approach; published by US-CERT in 2012, checked November 3, 2026. This calculator does not treat 3-2-1 as a retention-period recommendation.
- WordPress Developer Resources: Backups — describes files and database as separate parts of a typical full site backup; checked November 3, 2026.
For repeated full-copy storage without incremental generations, use the backup space estimator. For site file and database size assumptions, see the WordPress resource needs estimator.
How it works
Enter measured full and average incremental backup sizes, days between full backups, days between incrementals, and the number of retention days. The calculator counts scheduled copies younger than the retention window and estimates their combined storage. Incremental intervals must divide evenly into the full interval.
Good to know
Does this calculator tell me how long I should retain backups?
No. It estimates capacity for the schedule and retention window you enter. Choose retention based on your recovery, operational, and policy needs, and verify your backup software's pruning behavior.
How are incremental sizes handled?
The calculation applies your entered average incremental size to each scheduled incremental copy. Actual incremental sizes can vary; use measurements from your backup system and allow for overhead separately.
Does this model prove that a backup can be restored?
No. It counts storage only. It does not validate backup integrity, chain dependencies, offsite copies, or restore procedures; test restores with your own system.
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