How this calculator works
This conservative model counts both backup schedules independently, including incremental runs on full-backup days. It assumes fixed backup sizes and does not deduct deduplication. Restore chains crossing the retention boundary may need extra older full backups.
The formula
Full count = ceiling(retention/full interval). Incremental count = ceiling(retention/incremental interval). Storage = counts × corresponding sizes, then add buffer.A quick example
A 30-day window with 100 GB full backups every seven days and 5 GB daily incrementals budgets five full and thirty incremental backups: 650 GB, or 780 GB with a 20% buffer.
How to use this calculator
- Choose the settings that match your scenario, using the units shown beside each field.
- Enter full backup size (gb), days between full backups, incremental backup size (gb), days between incremental backups.
- Calculate, then review the method and assumptions alongside the results.
A few common questions
Does this guarantee a restorable backup set?
No. Retention must preserve the complete dependency chain, and restores should be tested independently.
Can I use compressed backup sizes?
Yes. Enter measured stored sizes consistently for both full and incremental backups.