99.9% uptime: how much downtime?
An uptime of 99.9% (three nines) allows 43m 48s of downtime a month and 8h 45m 36s a year.
| Period | Allowed downtime |
|---|---|
| Per day | 1m 26s |
| Per week | 10m 5s |
| Per month | 43m 48s |
| Per quarter | 2h 11m 24s |
| Per year | 8h 45m 36s |
What 99.9% means in practice
The most common target for SaaS. About 44 minutes a month is enough for a short incident and a rollback, but a long outage breaks it.
A year is counted as 365 days and a month as a twelfth of that. Need another percentage, or the uptime from minutes of downtime? Use the uptime calculator.