Count retained copies, not backup runs
Enter the full copies kept at the same time and the total retained incremental days across those copies. Daily changed data means bytes stored by an incremental run, which can differ from the size of newly created files. A large database rewrite may produce a large increment even if the database hardly grows.
The stored-size ratio is measured backup size divided by original size. Use 100% when unknown. A ratio above 100% allows for packaging or encryption overhead. This planning model assumes additive full and incremental storage; it does not model deduplication, synthetic fulls, differential chains or per-version retention rules.
Space is only one part of recovery
Headroom is extra capacity, not extra backup copies. The monthly figure applies the entered rate to capacity including headroom, so it is a reserved-capacity budget rather than a precise usage invoice. Retrieval, requests, outbound transfer, taxes and minimum retention charges are excluded. Check storage pricing components for your provider.
A storage estimate cannot establish that backups are restorable. Keep a tested restore procedure and confirm which full copy each increment needs before deleting anything. Use upload time for the transfer window and bandwidth cost for outbound charges.