⌚ About 2 min read
Turn an availability percentage into understandable downtime and verify contractual exclusions.
Before you start
Work on a copy or a controlled test when the change can affect production. Keep timestamps, screenshots and the previous configuration so the result can be compared.
Step by step
- Identify the SLA measurement period: month, quarter, or year.
- Calculate downtime fraction as one minus the SLA percentage.
- Multiply that fraction by the total duration of the period.
- Compare it with downtime measured by monitoring.
- Review exclusions such as maintenance, force majeure, dependencies, and uncovered windows.
Validation
Repeat the original test after the change and confirm that the expected service works without creating a new regression. Document the final state.
SLA: convert a percentage into minutes over the correct period
Technical checkpoints
- Allowed downtime = total period × (1 - availability). The result depends directly on the contractual measurement period.
- 99.9% per month is not equivalent to 99.9% measured annually for monthly incident handling.
- Planned maintenance, force majeure or dependencies may be contractually excluded; technical calculation must reflect SLA rules.
30-day example
Over 30 days: 43,200 minutes. At 99.9%, theoretical maximum downtime is 43.2 minutes.
43,200 × (1 - 0.999) = 43.2 min
99.99% => 4.32 minTopic-specific pitfalls
- Rounding too early can create several minutes of error over a long period.
- Monitoring and contract may define outage start/end differently.
How to validate
- Measurement period, timezone, exclusions and data source are explicitly documented.
- The calculation can be reproduced from raw monitoring timestamps.