Uptime SLA Downtime Calculator
A service level agreement (SLA) usually promises an uptime percentage like 99.9 percent. The flip side is the downtime budget: how long the service is allowed to be unavailable. That budget is just the period length times the downtime fraction. Enter your uptime target as a percentage and this calculator returns the allowed downtime per day, per week, per 30-day month, and per 365-day year. It is a deterministic conversion, so the figures are exact for the periods shown.
SLA downtime formula
Downtime fraction = 1 - (uptime % / 100)
Downtime per period = period length * downtime fraction
Per day = 1,440 minutes * fraction
Per month = 43,200 minutes (30 days) * fraction
Per year = 525,600 minutes (365 days) * fraction
Results are shown in minutes. Each extra nine in the uptime target cuts the allowed downtime by roughly a factor of ten.
Uptime tier context
- 99 percent (two nines): about 3.65 days of downtime per year.
- 99.9 percent (three nines): about 8.77 hours per year.
- 99.99 percent (four nines): about 52.6 minutes per year.
- 99.999 percent (five nines): about 5.26 minutes per year.
- Confirm whether your SLA uses 30-day or calendar months and excludes maintenance windows.
Uptime SLA calculator: frequently asked questions
How much downtime does 99.9 percent uptime allow?
An uptime of 99.9 percent (three nines) allows 0.1 percent downtime. Over a 365-day year that is about 8 hours 45 minutes, over a 30-day month about 43 minutes 12 seconds, and over a week about 10 minutes 5 seconds. The allowed downtime scales directly with the period length.
What are the common uptime tiers?
The 'nines' shorthand is common: 99 percent (two nines) allows about 3.65 days per year, 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 per year. Each extra nine cuts allowed downtime by roughly a factor of ten.
How is allowed downtime calculated?
Allowed downtime equals the period length times one minus the uptime fraction. For 99.95 percent over a 30-day month, that is 30 days times 0.0005, which is 0.015 days, equal to about 21 minutes 36 seconds.
Does the SLA period use 30 days or the actual month length?
It depends on the agreement. Many SLAs define a month as 30 days or use the actual calendar month. This calculator lets you set the period in days so you can match the exact definition in your contract, whether 28, 30, 31, or 365 days.
Is scheduled maintenance counted as downtime?
That depends on the SLA terms. Some agreements exclude announced maintenance windows from the downtime budget, others do not. This tool computes the raw allowed downtime for a given uptime target; check your contract for what counts against it.
Official sources
- NIST: National Institute of Standards and Technology, system availability concepts.
- U.S. General Services Administration: GSA service level standards reference.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.