Uptime SLA Downtime Calculator
An uptime SLA, such as 99.9 percent, sets a ceiling on how long a service may be unavailable. Converting that percentage into real time tells you how tight the target is and how much outage budget you have. Enter the SLA percentage and the days you count as a month, and this calculator shows the maximum allowed downtime per day, per week, per month, and per year, in a readable breakdown plus total minutes.
Allowed downtime formula
downtime fraction = 1 - (SLA / 100)
period seconds = days * 86,400
allowed downtime = period seconds * downtime fraction
week = 7 days, month and year are user-set
Each result is shown as a readable hours, minutes, and seconds breakdown. The downtime fraction is the part of the period the service may be unavailable.
Allowed downtime per year (365 days)
- 99 percent: about 3.65 days.
- 99.9 percent (three nines): about 8 hours 46 minutes.
- 99.95 percent: about 4 hours 23 minutes.
- 99.99 percent (four nines): about 52 minutes 36 seconds.
- 99.999 percent (five nines): about 5 minutes 15 seconds.
Uptime SLA: frequently asked questions
How is allowed downtime calculated from an SLA?
Allowed downtime is the period length times one minus the uptime fraction. For a 99.9 percent SLA, the allowed downtime fraction is 0.001. Over a 30-day month that is 0.001 times 43,200 minutes, or about 43.2 minutes.
How much downtime do common SLA tiers allow per year?
Per 365-day year: 99 percent allows about 3.65 days, 99.9 percent (three nines) about 8.77 hours, 99.99 percent (four nines) about 52.6 minutes, and 99.999 percent (five nines) about 5.26 minutes. Each extra nine cuts the allowed downtime by roughly a factor of ten.
Does this use a 30-day month or a calendar month?
The monthly figure uses a configurable days-per-month input that defaults to 30. Many cloud providers calculate SLA credits on the actual days in the billing month, so set it to 28, 29, 30, or 31 to match the month in question.
Is downtime measured against scheduled maintenance?
It depends on the SLA wording. Some providers exclude scheduled maintenance windows from the downtime calculation, others do not. This calculator computes the raw allowed downtime for the percentage; check your contract for what counts as downtime.
Sources and definitions
- Allowed downtime is the period length times the complement of the uptime fraction. This is a standard arithmetic definition of an availability target.
- National Institute of Standards and Technology: SI units reference (time in seconds).
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.