Backup Time Calculator
The initial seed, the nightly delta, and the weekly cadence — backup windows priced on the wire you have.
Backup Time Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- One division per lane — no file-count overhead modeled
- Rate is the wire's real delivery, not the sheet
In short: A 500 GB seed over the gigabit line every NAS actually delivers — about 110 MB/s — is 4,545.454545 seconds: 1 h 15 min 45 s. The nightly incremental where 5% changed is 25 GB and lands in 3 min 47 s, and the weekly cadence of one full plus six incrementals costs 1 h 38 min 29 s of wire time a week. Plan the first run on the full; plan your life on the delta.
Formula
full seconds = GB × 1,000 ÷ MB/s ··· delta seconds = (GB × changed%) × 1,000 ÷ MB/s
Backup time is the transfer division at the wire's honest rate: gigabit Ethernet is sold as 125 MB/s and delivers 110–115 in real file copies once TCP and filesystem overhead take their share, which is why the default rate is 110 rather than the sheet number. The weekly cadence assumes the classic shape — one full seed, then nightly deltas of the changed share — and the small-file caveat rides on top: millions of tiny files can halve the throughput the big-file division predicts.
Worked Example
- Enter the full dataset size.
- Enter the throughput you have actually measured.
- Set the daily changed share.
- Read the seed, the delta and the weekly cost.
Defaults: 500 GB at 110 MB/s → 1 h 15 min 45 s seed, 3 min 47 s nightly at 5% changed. Drive the rate to 400 — USB-3 SSD class — and the same seed drops to 20 min 50 s.
Strengths & Limits Of This Model
Where this engine is strong
- Seed, delta and cadence priced separately
- Gigabit's honest 110 default, named
Where it stops
- Small-file workloads can land far below the division
Practical Use Cases
Overnight windows
will the seed land before dawn
NAS shopping
gigabit vs 2.5 GbE, priced in hours
Retention design
full-plus-delta weekly cost
Methodology & Editorial Standards
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
Backup Time Calculator — 8 Expert FAQs
8 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
How long does a 500 GB backup take?
At the 110 MB/s a real gigabit wire delivers, 500 GB is 4,545.454545 seconds — 1 h 15 min 45 s. The same copy over a USB-3 SSD at 400 MB/s lands in about 20 min 50 s. The division never changes; only the rate does, which is why the measured rate belongs in the field, not the advertised one.
Why 110 MB/s and not the gigabit sheet figure?
Gigabit Ethernet is sold as 125 MB/s, but TCP acknowledgements, protocol overhead and filesystem work consistently leave real file copies at 110–115 MB/s — a fraction measured across home NAS transfers for years. Planning the seed at the sheet rate buys an overnight window that ends an hour late.
Should backups be full or incremental?
The classic cadence is one full seed, then nightly incrementals of the changed share, then a fresh full on a slower schedule — the weekly line prices that shape. Incrementals keep the nightly window small; the periodic full keeps restore chains short. Both sides of the trade price through this calculator.
Why is my backup much slower than the calculator?
Millions of small files kill throughput — each one pays open-close-metadata overhead that the big-file division never sees, and backup software that walks directories serially can drop an order of magnitude below the wire rate. The number here is the wire's honest ceiling, not every workload's floor.
How long to back up to an external USB drive?
A USB-3 hard drive usually delivers 90–110 MB/s when the drive itself is the limiter, and a USB-3 SSD 400–450 MB/s — enter the class you own. USB-2 at about 35 MB/s turns the 500 GB seed into a day-long project, which is why that port is a restore lane, not a backup lane.
Does compression change backup time?
It trades wire bytes for CPU: compressing before the copy can shrink a text-heavy 500 GB set several times over, and the compression ratio page prices that squeeze. Duplicating first shrinks it further. Both wins vanish on media that is already squeezed, so measure the changed share after the pipeline, not before.
How do I size the backup window for a office server?
Take the full size and the measured rate, seed the calculator, and confirm the full lands inside the quiet hours with margin — the nightly delta then fits almost anywhere. If the seed cannot fit the window, seed once over a weekend and run incrementals forever after; the weekly line shows that steady state.
What rate should I plan for over Wi-Fi?
Real Wi-Fi varies too much to preset — from under 20 MB/s on crowded old gear to beyond gigabit on a clean Wi-Fi 6 link. Measure one real copy, enter that number, and keep the wired figure for the comparison. A backup lane that changes speed every evening deserves the slow honest number.