Uptime SLA Calculator

A 99.99% SLA (often called "four nines") allows 52 minutes and 36 seconds of downtime per year, or approximately 4 minutes and 23 seconds per month. This includes all downtime, whether planned maintenance or unexpected outages. Achieving four nines requires redundant infrastructure, automated failover, and rigorous change management. Most cloud providers guarantee 99.95-99.99% for individual services.

Downtime costs vary dramatically by business type. Gartner estimates the average cost of IT downtime at $5,600 per minute ($336,000/hour). For e-commerce, Amazon famously calculated that every minute of downtime costs $220,000 in lost sales. For SMBs, the cost includes lost sales, employee idle time, recovery effort, and reputation damage. Even a $1M revenue company loses approximately $114 per hour of downtime in direct revenue, plus indirect costs 2-5x that amount.

For 99.9% (three nines): a single server with monitoring, automated backups, and a recovery plan allowing 8 hours 45 minutes of downtime per year. For 99.99% (four nines): you need active-passive or active-active high availability with automated failover, load balancers, database replication, and zero-downtime deployment. The cost jump from three nines to four nines is typically 3-5x your infrastructure spending.

It depends on the provider. Most enterprise cloud SLAs exclude scheduled maintenance windows from their uptime calculations. However, from your users' perspective, planned downtime is still downtime. Best practice: use rolling deployments and blue-green deployment strategies to achieve zero-downtime maintenance. This way, even planned updates do not impact your actual uptime.

Uptime refers to the total time a system is operational. Availability is the percentage of time a system is accessible and functioning correctly for end users. A server can be "up" but unavailable if the network connection is down or the application has crashed. True availability monitoring checks the full request path: DNS resolution, network connectivity, application response, and response correctness. SLA calculations should be based on availability, not just server uptime.

Multi-region deployments achieve higher availability by eliminating single points of failure at the infrastructure level. If one AWS region goes down (which happens rarely but has occurred), traffic automatically routes to another region. Theoretical availability of two independent regions with 99.9% each is 99.9999% (1 - (0.001 x 0.001)). The trade-offs are higher cost (2x or more), data synchronization complexity, and increased operational overhead. Multi-region is typically justified only when targeting 99.99% or higher.