MTBF Calculator calculates mean time between failures (MTBF) of a product.

Mean time between failures (MTBF) is the mean (average) time between failures of a system, the reciprocal of the failure rate in the special case when the failure rate is constant. Calculations of MTBF assume that a system is 'renewed', i.e. fixed, after each failure, and then returned to service immediately after failure.

A related term, mean distance between failures, with a similar and more intuitive sense, is widely used in transport industries such as railways and trucking. The average time between failing and being returned to service is termed mean down time (MDT).