Uptime / SLA Calculator
Convert uptime SLA percent (99.9% etc.) into allowed downtime per day/week/month/year.
SLA, uptime and allowed downtime
A Service Level Agreement defines the minimum uptime a provider commits to. Allowed downtime for a given period follows downtime = (1 − SLA) · period. Over a year (8,760 h): 99% tolerates 87.6 h (3.65 days); 99.9% (three nines) 8.76 h; 99.99% (four nines) 52.6 min; 99.999% (five nines) only 5.26 min. Each extra nine costs exponentially more — it forces redundancy, multi-AZ, multi-region and active-active topologies. Composite availability: a service depending on three components at 99.9% each has an effective SLA of roughly 99.7% (0.999³).
Applications and context
Used to compare cloud providers (AWS EC2 99.99%, S3 Standard 99.9% availability, Cloudflare and Fastly CDNs), to configure uptime monitors (Pingdom, StatusCake, UptimeRobot), to claim SLA credits when targets are missed, to design microservice architectures and to pick between regions.
FAQ
What does "three nines" mean? It's shorthand for 99.9% uptime — roughly 8.76 hours of downtime per year or 43.8 minutes per month.
Why is each extra nine so expensive? Going from 99.9% to 99.99% cuts allowed downtime by 10×, which usually requires hot standby, multi-region replication and tighter operational discipline.
Do scheduled maintenance windows count? Most providers exclude announced maintenance from the SLA — read the contract before claiming credits.
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