Free Uptime Downtime calculator with clear step-by-step results.
Converts an availability target into a concrete error budget in minutes, tracks what has been spent, and derives mean time to restore from incident count. Framing availability as a budget rather than a promise is what makes it possible to trade reliability against release velocity.
Error budget
Allowed minutes = period days x 1440 x (1 - uptime target)
Mean time to restore
MTTR = total downtime minutes / number of incidents
About 43.2 minutes per 30-day month, or 8.76 hours a year. Each additional nine divides that by ten - 99.99% allows just 4.3 minutes a month.
The usual convention is to freeze feature releases and spend engineering effort on reliability until the budget recovers in the next window.