Uptime Calculator

What does "99.9% uptime" actually mean?
See the real numbers behind SLA percentages.

%

Allowed Downtime

Per Day —
Per Week —
Per Month —
Per Year —

Common SLA Comparison

Uptime Downtime/Year Downtime/Month
99% 3.65 days 7.3 hours
99.9% 8.76 hours 43.8 minutes
99.95% 4.38 hours 21.9 minutes
99.99% 52.6 minutes 4.4 minutes
99.999% 5.26 minutes 26 seconds

Understanding uptime

The "nines" shorthand

IT folks often talk about "three nines" (99.9%) or "four nines" (99.99%). Each additional nine represents a 10x reduction in allowed downtime.

What SLAs don't tell you

99.9% uptime sounds great until you realize that's 43 minutes of downtime per month. If that happens during business hours, it matters a lot more.

Scheduled vs unplanned

Some providers exclude "scheduled maintenance" from uptime calculations. Always read the fine print on what counts as downtime.

Real-world context

Five nines (99.999%) is extremely difficult to achieve and expensive to maintain. For most small businesses, 99.9% with good monitoring is plenty.

Need help evaluating hosting providers or designing for reliability?

Let's talk
← Back to all tools