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Backup Retention Storage Calculator

Calculate retained backup storage, full and incremental counts, and estimated monthly storage cost.

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Backup retention storage calculator

Estimate backup storage from source data size, daily change rate, retention, full backup frequency, and data reduction.

2.5 means 2.5:1 data reduction
Estimated stored data
13.23 TB
After reduction and buffer
Monthly storage cost
$264.5
Stored TB × cost
Full backups retained
5
Conservative count
Incrementals retained
25
Daily restore points
Use real backup reports once available; data reduction ratios vary heavily by workload and backup product.

What this estimate does and does not do

This calculator is a capacity-planning estimate for backup repositories. It does not replace sizing from your backup product, appliance vendor, or cloud provider. Real storage depends on backup mode, synthetic fulls, active fulls, changed-block tracking, deduplication scope, compression, encryption, immutability, metadata, failed jobs, and workload mix.

Formula used

full backups retained = floor(retention days / full backup frequency) + 1
incrementals retained = retention days - full backups retained
full backup size = source data / reduction ratio
incremental size = source data × daily change rate / reduction ratio
stored backup = (full count × full size + incremental count × incremental size) × buffer factor

Worked example

For 5 TB of source data, 3% daily change, 30-day retention, weekly full backups, 2.5:1 data reduction, and 15% buffer:

fulls = floor(30 / 7) + 1 = 5
incrementals = 30 - 5 = 25
full size = 5 / 2.5 = 2 TB
incremental size = 5 × 0.03 / 2.5 = 0.06 TB
stored = (5 × 2 + 25 × 0.06) × 1.15 ≈ 13.23 TB

Assumptions

  • The model is intentionally conservative about full backup count.
  • Reduction ratio combines compression and deduplication into one editable factor.
  • It does not model GFS retention, monthly/yearly archives, object-lock overhead, erasure coding, replication, or offsite copies.
  • Use monitoring and repository reports once the system is running.

Frequently asked questions

How is backup retention storage estimated?

The calculator estimates retained full backups plus retained incremental backups, then applies a combined compression/deduplication ratio and buffer percentage.

What daily change rate should I use?

Many environments use a planning range of roughly 2–10%, but databases, VM churn, logs, and media workflows can be much higher. Use real backup reports when available.

What does the reduction ratio mean?

A 2.5:1 reduction ratio means 2.5 TB of logical backup data is expected to consume about 1 TB of physical storage after compression and deduplication.

Is this a vendor-accurate sizing tool?

No. It is a planning estimate. Backup products differ in synthetic fulls, incrementals, dedupe scope, immutability overhead, metadata, and retention behaviour.