What the percentage means
Availability is the proportion of time a service is usable during a defined period. A target such as 99.9% does not by itself explain which users, features or maintenance windows are included.
The calculator uses calendar minutes and a simple percentage. Contracts and internal objectives may calculate service availability differently.
Questions behind an availability target
- What counts as unavailable or degraded?
- Are planned maintenance windows excluded?
- Is availability measured for the whole service or individual components?
- Which monitoring source is authoritative?
- How are partial and regional failures treated?
Limits of the estimate
The result does not predict actual outages or prove that an architecture can meet the target. A service may experience many short interruptions or one long event and still produce the same total downtime.
Pair availability targets with recovery objectives, service-impact definitions and tested failover procedures.