Uptime Calculator
Calculate uptime percentage, allowed downtime, and SLA metrics from uptime ratio or downtime duration over any period.
How Uptime Percentage Is Calculated
Uptime measures how much of a monitoring window a service stayed available. SLA contracts express this as a percentage such as 99.9%, which translates to a fixed amount of allowed downtime over the period.
Uptime Formula
$$\text{uptime \%} = \frac{\text{total time} - \text{downtime}}{\text{total time}} \times 100$$ $$\text{downtime} = \text{total time} \times \left(1 - \frac{\text{uptime \%}}{100}\right)$$Example: 43 minutes of downtime in 30 days equals 99.9002% uptime. A 99.9% SLA over 30 days allows about 43.2 minutes of downtime.
Frequently Asked Questions
How much downtime is allowed for 99.9% uptime in 30 days?
About 43.2 minutes. That is 0.1% of 30 days (43,200 minutes).
What is the difference between 99%, 99.9%, and 99.99%?
Each extra nine reduces allowed downtime by a factor of ten. 99% allows 1% downtime, 99.9% allows 0.1%, and 99.99% allows 0.01%.
Can I enter uptime percentage instead of downtime?
Yes. Switch input mode to enter uptime percentage and the calculator returns the equivalent downtime for your selected period.
Does planned maintenance count as downtime?
That depends on your SLA definition. Some contracts exclude scheduled maintenance windows; others count all unavailable time.
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