Uptime and SLA calculator
Enter a percentage to see how much downtime it allows, or enter downtime to see the percentage. Useful for writing an SLA or checking a host’s promise.
Measure your real uptime
From 15 locations, checked every minute. 650,000 free credits every month.
What is uptime?
Uptime is the share of time a service works, as a percentage. 99.9% sounds close to perfect, but it allows almost 44 minutes of downtime a month. Each extra nine cuts the allowed downtime by ten.
| Uptime | Per day | Per week | Per month | Per year |
|---|---|---|---|---|
| 99% | 14m 24s | 1h 40m 48s | 7h 18m 20s | 3d 15h 39m |
| 99.5% | 7m 12s | 50m 24s | 3h 39m 10s | 1d 19h 49m |
| 99.9% | 1m 26s | 10m 4s | 43m 50s | 8h 45m 57s |
| 99.95% | 43s | 5m 2s | 21m 55s | 4h 22m 58s |
| 99.99% | 8.6s | 1m | 4m 23s | 52m 35s |
| 99.999% | 0.86s | 6s | 26s | 5m 15s |
Simple arithmetic, stated plainly.
Allowed downtime is (100% − uptime) × the length of the period. We count a day as 24 hours, a week as 7 days, a month as 30.44 days, a quarter as 91.31 days and a year as 365.25 days, the averages over a leap-year cycle. Contracts often use a 30-day month instead, which gives slightly less downtime; check which one yours uses.
What does 99.9% uptime mean?
At most about 44 minutes of downtime a month, or 8 hours 46 minutes a year.
What are «five nines»?
99.999% uptime: about 5 minutes a year. It needs redundancy everywhere and is rare outside telecoms and large clouds.
What counts as downtime in an SLA?
Whatever the contract says. Many exclude planned maintenance and count only outages longer than a few minutes, so read the definitions before comparing percentages.
How do I measure my own uptime?
With checks from outside, at a fixed interval, from more than one place. One location can’t tell a real outage from a bad route; we confirm from three continents before counting a minute as down.