Is anything sent to a server?

No. The calculation is simple arithmetic (window length × (1 − availability/100)) and runs entirely in your browser. Nothing is uploaded or stored.

How is a month defined here?

As a fixed 30-day window (the label reads Per month (30d)), and a year as 365 days. Real calendar months vary from 28 to 31 days, so contractual SLAs measured per calendar month will differ slightly from the 30-day figure shown.

What does another nine actually buy?

Each added nine cuts allowed downtime by 10×. At 99.9% you get about 8.8 hours of downtime per year; at 99.99% about 52.6 minutes; at 99.999% about 5.3 minutes — typically achievable only with automated failover, since human response alone is too slow.

Calculadora de Disponibilidade SLA

Overview

SLA targets are quoted in nines, but engineering decisions need minutes. This calculator converts an availability percentage into the downtime it permits over four windows: per year (365 days), per month (30 days), per week, and per day. Results are formatted in the most readable unit — ms, seconds, minutes, hours, or days. Use it to sanity-check a contract before signing, or to translate an internal SLO into an on-call reality.

How to use

Type a percentage into Availability (%) — any value from 0 to 100, down to 0.001 steps.
Or click a preset button: 90%, 95%, 99%, 99.9%, 99.95%, 99.99%, 99.999%.
Read the allowed downtime under Per year, Per month (30d), Per week, and Per day — the figures update instantly.

Examples

99.9 → 8.8 h per year, 43.2 min per month (30d)
99.99 → 52.6 min per year, 4.3 min per month (30d)
99.999 → 5.3 min per year, 25.9 s per month (30d)

Notes

The math assumes downtime accrues evenly: allowed downtime = window × (1 − availability/100). Contracts often exclude planned maintenance or measure per calendar month, so read the SLA’s measurement clause before comparing against these numbers. Values outside 0–100 show an error instead of results.