Uptime Calculator: SLA percentage to allowed downtime

Enter an uptime percentage to see how much downtime it allows per day, week, month, quarter and year. Or enter the minutes of downtime you had in a month to see the uptime percentage. Free, runs in your browser, no signup.

From promise to measurement

Track your real uptime — Zuzia checks your site from Poland, New York and Singapore.

Allowed downtime for common SLA levels

Downtime allowed at each uptime level. A month is the average month of 30.44 days, a quarter is three of them and a year is 365 days.

Uptime	Per day	Per week	Per month	Per quarter	Per year
99%	14m 24s	1h 40m 48s	7h 18m 20s	21h 55m	3d 15h 36m
99.5%	7m 12s	50m 24s	3h 39m 10s	10h 57m 30s	1d 19h 48m
99.9%	1m 26s	10m 5s	43m 50s	2h 11m 30s	8h 45m 36s
99.95%	43s	5m 2s	21m 55s	1h 5m 45s	4h 22m 48s
99.99%	9s	1m	4m 23s	13m 9s	52m 34s
99.999%	864 ms	6s	26s	1m 19s	5m 15s

For a fixed 30-day month, use the calculator above: 99.9% gives 43m 12s.

What is an SLA and how do you calculate downtime

A service level agreement (SLA) states how much of the time a service should be available, usually as a percentage over a month or a year. The higher the percentage, the less downtime you can tolerate before the provider owes you something, often a service credit.

The formula is simple: allowed downtime = (100 − uptime %) ÷ 100 × length of the period. For 99.9% over a 30-day month that is 0.001 × 30 × 24 × 60 = 43.2 minutes. To go the other way, uptime % = (period − downtime) ÷ period × 100.

The result depends on the period you pick. This page uses 30 days, the average month of 30.44 days (365.25 ÷ 12, rounded), a quarter of three average months and a year of 365 days. Compare SLAs using the same period, and check whether the agreement excludes maintenance windows.

Frequently asked questions

How much downtime is 99.9% uptime?

99.9% uptime allows 43 minutes and 50 seconds of downtime in an average month of 30.44 days, 10 minutes and 5 seconds per week and 8 hours 45 minutes 36 seconds per 365-day year. Over a 30-day month it is 43 minutes and 12 seconds.

What is the difference between 99.9% and 99.99%?

Each extra nine cuts the allowed downtime by a factor of ten. At 99.9% you may be down about 8 hours 46 minutes a year. At 99.99% it is about 52 minutes a year, and at 99.999% about 5 minutes.

Does planned maintenance count as downtime?

It depends on the agreement. Many SLAs exclude announced maintenance windows, others count every minute the service is unavailable. Check how your SLA defines downtime and what it excludes before you compare numbers.

Does a 99.9% SLA mean my site will really be up 99.9% of the time?

No. An SLA is a promise with a remedy, usually a service credit, not a measurement. Your real uptime is what independent checks record, so measure it from outside your own network and from more than one location.

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