Free Tools / Uptime SLA Calculator
Uptime SLA Calculator
"Three nines" sounds reassuring until you see it in minutes. Pick a service level to see exactly how much downtime it allows per day, week, month, and year, or work backward from your own outage to the uptime you achieved.
Allowed downtime for a service level
| Period | Allowed downtime |
|---|
What uptime did I achieve?
The "nines", at a glance
- 99% (two nines): about 3.65 days of downtime per year. Fine for internal tools, not for customer-facing systems.
- 99.9% (three nines): about 8 hours 46 minutes per year. A common baseline SLA.
- 99.99% (four nines): about 52 minutes per year. Needs redundancy and automated failover.
- 99.999% (five nines): about 5 minutes per year. Serious high-availability engineering.
The catch: higher nines cost more, and the jump from three to four nines is where most of the engineering work lives. The right target is the one your business actually needs, not the biggest number.
Frequently asked questions
How much downtime does 99.9% uptime allow?
A 99.9% SLA (three nines) allows about 43 minutes 50 seconds of downtime per month, or roughly 8 hours 46 minutes per year.
What does 99.99% uptime mean?
99.99% (four nines) allows about 4 minutes 23 seconds of downtime per month, or roughly 52 minutes 36 seconds per year. It usually requires redundancy and automated failover.
How do I calculate my achieved uptime?
Divide the time the service was up by the total time in the period, then multiply by 100: uptime % = (period - downtime) / period x 100.
Picking a realistic SLA and building the monitoring and redundancy to meet it is core platform-engineering work. Talk to us or see our other free tools.