SLA Uptime and Downtime Calculator
See how much downtime a given SLA actually allows.
Your numbers
Your results
Per day
Per day
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Per week
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Per month (30 days)
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Per year (365 days)
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Number of nines
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SLA Uptime and Downtime Calculator by TheCalcTools
How the SLA Uptime and Downtime Calculator works
Enter the availability promised in the SLA.
The allowed downtime is the unavailable fraction times the length of the period.
A 30-day month and a 365-day year are used.
The formula
downtime = (1 − availability) × period
Worked example
Using the default values shown in the calculator:
| Availability (%) | 99.9 |
|---|
- 99.9% availability means 0.1% unavailable.
- Per day: 0.1% of 86,400 s = 0h 1m 26.4s.
- Per year: 8h 45m 36.0s, usually quoted as about 8.76 hours.
Result:
| Per day | 0h 1m 26.4s |
|---|---|
| Per week | 0h 10m 4.8s |
| Per month (30 days) | 0h 43m 12.0s |
| Per year (365 days) | 8h 45m 36.0s |
| Number of nines | 3.00 |
Frequently asked questions
What is five nines?
99.999% availability, which allows about 5 minutes 15 seconds of downtime per year.
Does an SLA guarantee that downtime?
Usually not. SLAs typically promise service credits if the target is missed. Check how the provider measures downtime and which exclusions apply.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.