Reliability planning tool
SLA uptime calculator
See how much downtime an uptime promise allows. Choose a common SLA or enter your own percentage.
Enter a number from 0 to 100.
Allowed downtime
These are mathematical allowances. Your provider’s SLA may define exclusions, maintenance windows, and service credits differently.
What does 99.9% uptime mean?
A 99.9% uptime target allows about 43 minutes of downtime in a 30-day month or 8 hours and 46 minutes in a 365-day year. Each extra nine cuts the allowed downtime by roughly a factor of ten.
Use the same measurement period as your contract. A monthly SLA is normally judged month by month; it is not automatically averaged over a full year.
How the calculation works
Allowed downtime = period length × (1 − uptime percentage / 100). For example, at 99.99% uptime, the unavailable share is 0.01% of the period.