Uptime Calculator

"Nines" is industry shorthand for the number of 9s in an SLA percentage. 99% is "two nines," 99.9% is "three nines," 99.99% is "four nines," and 99.999% is "five nines." Each additional nine reduces allowed downtime by roughly 10x. Five nines (99.999%) allows only about 5 minutes and 15 seconds of downtime per year.

Downtime is calculated as: downtime = (1 - uptime_percentage / 100) x total_time_in_period. For a year, the total time is 525,960 minutes (365.25 days x 24 hours x 60 minutes). For a month, it is 43,830 minutes (525,960 / 12). The result is then broken down into days, hours, minutes, and seconds.

AWS EC2, Azure VMs, and GCP Compute Engine all offer SLAs of 99.99% (four nines) for multi-AZ/multi-zone deployments, and 99.9% (three nines) for single-instance deployments. Managed services like S3 and Cloud Storage typically offer 99.9% to 99.99% depending on the storage class. Always check the provider's current SLA documentation for exact terms.

An error budget is the inverse of an SLA — it is the total amount of allowed downtime or errors within a given period. For example, a 99.9% SLA gives you an error budget of 0.1%, which equals approximately 43.8 minutes per month. SRE teams use error budgets to balance reliability work against feature development: if the budget is spent, new releases are frozen until reliability improves.

It depends on the provider and the specific SLA contract. Most major cloud providers exclude scheduled maintenance windows from their SLA calculations. However, from a user experience perspective, downtime is downtime regardless of whether it is planned. Many teams track both contractual SLA and actual availability separately.

Yes. All calculations run entirely in your browser using JavaScript. No SLA percentages, downtime values, or any other data is ever sent to any server. You can verify this by checking the Network tab in your browser's developer tools while using the tool.

Switch to the "Downtime to SLA" tab. Enter your maximum acceptable downtime in minutes or hours, select the time period (year, month, week, or day), and the tool will calculate the required SLA percentage. For example, entering 10 minutes per month gives you approximately 99.977% SLA.