Mean Time between Failures (MTBF) is the average or mean time between system failures, often referred to as a device’s “useful life.” Calculation of MTBF is under the assumption that a system fixes itself after a failure, and then placed in service immediately after its breakdown. The average duration between failure and return to service is known as Mean Time to Repair (MTTR) or Mean Down Time (MDT).

MTBF differs from Mean Time to Failure (MTTF), and the interchanged use of these is erroneous. MTTF is the average duration until a system terminally fails and needed replacement, or until a product, design, or process’ operation collapses. MTBF is only for components that are still repairable and can eventually function.

Determine MTBF through the following formula:

MTBF = MTTF + MTTD (Mean Time to Diagnose) + MTTR (Mean Time to Repair)

Commercial products describe the MTTF Lifetime as the duration that a product lasts, assuming its proper usage.

MTBF value qualification is an integral element in product development. Reliability and design engineers often use Reliability Software to compute product MBTFs through various standards.

The utilization of MTBF in the technological industry has always been in question due to its inaccuracy in terms of application to actual systems and the uncertainty of the culture that it embodies. Many system MTBFs are present in various databases, though these values are often imprecise. MTBF justifies a notion of a tolerable level of malfunction, thus eliminating the need to identify the root of a problem and taking measures to resolve it.

Organizations such as the British Royal Air Force are pursuing the development of other methods to calculate reliability such as the Maintenance-free Operating Period (MFOP). In addition, the National Aeronautics and Space Administration (NASA) is expanding its time-to-failure research with scenario- and condition- based techniques from the domain of prognostics.