Service Availability Calculator
Calculate uptime percentage from downtime minutes and see how it maps to the standard 'nines' of availability.
Inputs
e.g. 8760 hours for a full year, 720 for a month
Availability
99.991438%
Nines Rating
99.99% (four nines)
Uptime
525,555.00minutes
Allowed Downtime for 99.9% (over this period)
525.60minutes
Allowed Downtime for 99.99% (over this period)
52.56minutes
Step by step
Values used
Total Time Period = 8,760 hours; Total Downtime = 45 minutes
Availability percentage
availability = (total_time − downtime) / total_time × 100
Availability
= 99.991438
Nines Rating
= 99.99% (four nines)
Uptime
= 525,555.00 minutes
Allowed Downtime for 99.9% (over this period)
= 525.60 minutes
Allowed Downtime for 99.99% (over this period)
= 52.56 minutes
How it works
Availability is the fraction of a time period a service was up and functioning, expressed as a percentage. SLAs conventionally describe availability in terms of 'nines' — 99% ('two nines') permits about 3.65 days of downtime per year, while 99.999% ('five nines') permits only about 5.26 minutes per year — because each additional nine reduces allowed downtime by a factor of 10.
Formula
Availability percentage
availability = (total_time − downtime) / total_time × 100
- T
- total time in the period
- D
- total downtime in the period
Frequently Asked Questions
How much downtime does 99.9% availability allow per year?
99.9% ('three nines') allows about 8.76 hours of downtime per year (0.1% of 8,760 hours) — roughly 43.8 minutes per month.
How much downtime does 99.99% availability allow per year?
99.99% ('four nines') allows about 52.6 minutes of downtime per year — an order of magnitude tighter than three nines, which is why each additional nine is significantly more expensive to engineer for.
Does availability account for planned maintenance?
That depends on the SLA's definition — some exclude scheduled maintenance windows from the downtime count, while stricter SLAs count all unavailability, planned or not. Be explicit about which convention you're using when reporting a number.