What this calculator does
Inherent availability estimates the proportion of time a repairable item is available when only mean operating time and active corrective repair time are considered. It provides a transparent relationship between reliability and maintainability.
When to use it
Use it for early design trade-offs, a common reliability-maintainability discussion, or a first-pass uptime benchmark. It is most meaningful when MTBF and MTTR are based on the same failure scope.
Inputs and formula
Enter matching time units. A = MTBF ÷ (MTBF + MTTR)
Worked example and interpretation
An MTBF of 400 hours and MTTR of 8 hours yields 98.04% inherent availability. The result indicates the long-run ratio implied by the two means, not a production guarantee for the next shift.
Practical notes and limitations
Inherent availability excludes logistics, waiting for spares, administrative delay, planned outages, and external constraints. Operational availability is lower when those realities matter. Use MTTR definitions carefully and investigate material delays through MRO planning.