About this tool
Service availability is the percentage of a measurement period during which the service is considered available. It is commonly calculated from total period minutes minus qualifying downtime, divided by total period minutes.
The important operational detail is what counts as downtime. Contracts may exclude planned maintenance, customer-caused events, force majeure or specific upstream conditions. This calculator performs the math; the SLA language determines which minutes belong in the input.
How to use it
- Enter the measurement period in days.
- Enter the total qualifying downtime in minutes.
- Calculate and compare the result with the contractual or internal availability target.
Example: 30 days with 43.2 minutes downtime
Thirty days contain 43,200 minutes. Removing 43.2 minutes leaves 43,156.8 available minutes, which equals 99.9% availability.
Engineering notes
- Use the exact billing or SLA measurement period rather than assuming every month has 30 days.
- When reporting customer SLAs, keep an auditable record of excluded events and the contract clause used for each exclusion.
Frequently asked questions
What is the difference between 99.9% and 99.99%?
The extra nine dramatically reduces allowed downtime. Over 30 days, 99.9% allows 43.2 minutes while 99.99% allows about 4.32 minutes.
Does redundancy automatically guarantee a higher SLA?
No. Redundancy can improve resilience, but actual availability depends on design, failure modes, maintenance practices and operational response.
Should I use incident duration or customer-impact duration?
Use the duration defined by the SLA. A ticket may stay open after customer service is restored.