Uptime and downtime calculator (SLA)
Find out how much downtime an uptime SLA allows per year, month, week and day.
Each extra "9" slashes downtime: 99% allows ~3.65 days/yr; 99.9% ~8.76 h; 99.99% ~52.6 min; 99.999% ~5.26 min.
How the calculation works
Allowed downtime is the total period × (1 − uptime%). E.g., 99.9% of a year = 0.1% × 365.25 days ≈ 8.76 hours. That's why providers talk about "three nines", "four nines" and so on.
Examples
- 99.9% ("three nines") a year: ~8.76 h of allowed downtime.
- 99.99% ("four nines"): ~52.6 minutes per year.
Frequently asked questions
What does "five nines" mean?
99.999% uptime — only ~5 minutes of downtime per year. The standard for critical systems.
What is an SLA?
A Service Level Agreement — the contract where a provider promises a minimum uptime, with penalties or credits if missed.
Is paying for one more "nine" worth it?
Each extra nine costs much more and cuts little absolute downtime. Only worth it for truly critical systems.
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Updated on June 30, 2026 · by Rafael Rossi · Methodology & sources