Backup Size With Retention Calculator

Work out backup size with retention instantly with clear inputs, formula shown and shareable results.

About Backup Size With Retention Calculator

A grandfather-father-son scheme stores one full plus a chain of incrementals per cycle, repeated for the retention depth. Incrementals are small — daily change times full size — so most storage goes on repeated fulls. Recovery points are what retention actually buys, and restoring from a long incremental chain takes proportionally longer.

Formula

Backup storage

incremental = full x daily change; per cycle = full + incrementals x incremental; total = per cycle x fulls retained

Worked example

With the default values below, Backup Size With Retention Calculator returns Total backup storage of 3,776.0. Change any input above and every figure here is recalculated in your browser.

Inputs used

Full backup sizeminimum 0.001 GB: 800 GB
Daily change rateaccepts 0.001–100 %: 3 %
Full backups retainedminimum 1: 4
Incrementals between fullsminimum 0: 6

Results

Total backup storage: 3,776.0 GB
Storage per full-plus-incremental cycle: 944.0 GB
Size of each incremental: 24.00 GB
Recovery points available: 28

Step by step

1Values used
2Backup storage
3Total backup storage= 3,776.0 GB
4Storage per full-plus-incremental cycle= 944.0 GB
5Size of each incremental= 24.00 GB
6Recovery points available= 28

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why not keep only one full backup?

Because a corrupted full breaks every incremental that depends on it. Multiple independent fulls limit that blast radius.

What is a synthetic full?

The backup system merges a previous full with subsequent incrementals to create a new full without re-reading the source, which saves both backup window and source load.