Service-level agreements usually express availability as an uptime percentage. The percentage alone is hard to interpret operationally: 99.9% and 99.99% differ by only 0.09 percentage points, but their annual downtime budgets differ by almost eight hours. The calculator converts an SLA target into concrete daily, weekly, monthly, quarterly, and yearly allowances.
From Uptime Percentage to Downtime
Let \(p\) be the guaranteed uptime in percent and \(T\) the duration of the measurement period in seconds. The unavailable fraction is \(1-p/100\), so the allowed downtime is
\[ D=T\left(1-\frac{p}{100}\right). \]
For a 99.99% SLA, the unavailable fraction is \(0.0001\). Multiplying by one day gives
\[ 86400\cdot0.0001=8.64\text{ seconds}. \]
Over the mean Gregorian year of 365.2425 days, the same target permits approximately 52 minutes and 36 seconds of downtime.
Time Bases Used by the Calculator
A day contains 86,400 seconds and a week contains seven days. The monthly result is one twelfth of a mean Gregorian year; the quarterly result is one fourth. This keeps the monthly and yearly figures consistent rather than silently assuming every month has 30 days.
An SLA contract may use calendar months, fixed 30-day periods, or a custom billing window instead. When evaluating compliance, use the exact measurement period defined by the agreement rather than treating this calculator's normalized periods as contractual language.
Common SLA Levels
- 99%: approximately 3 days, 15 hours, and 39 minutes per year.
- 99.9%: approximately 8 hours and 46 minutes per year.
- 99.99%: approximately 52 minutes and 36 seconds per year.
- 99.999%: approximately 5 minutes and 16 seconds per year.
Availability Is More Than Arithmetic
A downtime budget does not by itself determine whether an incident violates an SLA. Agreements can exclude scheduled maintenance, customer-caused failures, force majeure events, or outages shorter than a sampling interval. They may also measure each region, endpoint, or calendar month independently.
The percentage should therefore be read together with the service-level indicator, measurement source, outage definition, maintenance policy, reporting window, and service-credit terms. The calculator answers the arithmetic question; the agreement defines which events count.