Uptime SLA Calculator

Take the unavailability fraction, which is 1 minus the uptime as a decimal, then multiply it by the length of the period. For a 99.9% SLA the fraction is 0.001, so over a 30.44-day month (2,629,800 seconds) you are allowed about 2,629.8 seconds, or roughly 43 minutes and 50 seconds of downtime.

Using a 365.25-day year, 99% (two nines) allows about 3 days 15 hours, 99.9% (three nines) allows about 8 hours 46 minutes, 99.99% (four nines) allows about 52.6 minutes, and 99.999% (five nines) allows about 5 minutes 16 seconds. Each extra nine cuts the allowed downtime to roughly one tenth of the previous level.

The calculator uses the average calendar month of 365.25 divided by 12, which is 30.4375 days, and a year of 365.25 days. This keeps the four budgets internally consistent, since 12 of these months equal exactly one year. If your SLA contract defines a fixed 30-day month or a specific billing cycle, the exact second count will differ slightly.

Switch to the achieved-uptime mode and enter how much downtime you observed over a day, week, month, or year. The calculator computes achieved uptime as (1 minus downtime divided by the period length) times 100. For example, 30 minutes of downtime in a month is about 99.9316% uptime.

That depends on the wording of your specific service agreement. Many SLAs exclude planned maintenance windows that are announced in advance, while unplanned outages always count. This calculator treats every second of downtime you enter the same way, so subtract any contractually excluded maintenance before you compare against the budget.