Define an availability measurement window

Percentages are meaningful only with a method.

Name the service being measured

Decide whether you are checking the homepage, a login flow, an API or an entire customer task. A homepage returning HTTP 200 does not prove that checkout or authentication works. Record the expected response and the locations from which observations are made.

Keep the denominator visible

A 30-day window contains 43,200 minutes, while a 31-day window contains 44,640. The same number of downtime minutes therefore produces a different percentage. State the start and end time, time zone and window length with every reported figure.

Handle partial and overlapping incidents

Two monitors reporting the same ten-minute outage do not necessarily create twenty minutes of downtime. Keep an incident timeline and define how overlap is merged. Record partial failures separately unless the measurement policy explicitly converts them into a single availability figure.

Distinguish observed availability from contractual terms

A contract may use a different scope, exclusions and reporting process. This calculator does not interpret those terms. Use it to understand the arithmetic and preserve the underlying observations so the result can be independently checked.