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Uptime SLA Downtime Calculator
Convert an uptime SLA percentage into the allowed downtime per day, week, month and year.
Uptime SLA
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How it works
Downtime = (1 − SLA%) × time period
An SLA percentage is the promised uptime; the rest is allowed downtime. The famous "number of nines" targets map to strict downtime budgets — 99.9% ("three nines") allows under 9 hours a year.
Worked example
99.9% uptime permits roughly 8.77 hours of downtime per year.
Frequently asked questions
What is "five nines"?
99.999% uptime — only about 5.26 minutes of downtime a year, which is very hard and costly to achieve.
Does planned maintenance count?
It depends on the SLA wording; many exclude scheduled maintenance windows from the downtime budget.
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This calculator is for educational purposes. Double-check important results before acting on them.