Uptime / SLA Calculator
Convert an SLA uptime percentage into allowed downtime per day, month and year.
About the Uptime / SLA Calculator
Enter an uptime percentage, such as the one in a hosting or cloud service level agreement (SLA). The calculator shows how much downtime that allows per day, week, month, quarter and year.
Each extra “nine” cuts allowed downtime tenfold: 99.9% (“three nines”) allows about 8.8 hours a year, 99.99% about 53 minutes and 99.999% about 5 minutes.
The formula
Downtime = (1 − uptime) × period
Worked example
A 99.9% SLA
- Downtime share: 0.1%
- Per month (30.44 days): 43 minutes 49 seconds
- Per year: 8 hours 45 minutes; at 99.99%, 52 minutes 35 seconds
Things to keep in mind
- Check how your provider defines the month and what counts as downtime; many exclude planned maintenance.
Questions people ask
Do services in series multiply?
Yes: two 99.9% services both needed give about 99.8%.
Does planned maintenance count?
Depends on the SLA; many exclude it.
What happens if the SLA is missed?
Usually a service credit, a partial refund of that month's fee, not compensation for your losses.