What Is the Mean Time to Repair (MTTR) and How Do You Calculate It?

What is MTTR

The Mean Time to Repair (MTTR), also known as the Mean Corrective Maintenance Time, is a measurement on the maintainability of equipment and repairable parts. It represents the average time needed to repair a failure until the equipment returns to a fully functional state.

A higher Mean Time to Repair may indicate that the replacement of a given asset is cheaper or preferable to reparing it. It may also suggest that you should store more spare parts for the equipment in question. Knowing how to reduce the MTTR is essential to avoid or minimise inactivity and the harm this may cause to your business.

So, how do you determine the MTTR?

It can be mathematically expressed by the division of the total corrective maintenance (CM) time during a given period by the number of corrective maintenance actions performed. This can be seen by the following formula:

It is worth noting that the total corrective maintenance time (and therefore, the Mean Time to Repair) can range from the discovery of the failure to the actual moment the reparation works start (this includes the time spent in identification, notification, acknowledgment and diagnostic of the failure). When it incorporates all of these other steps, it can also be referred to as Mean Time to Recovery. For this reason, an explicit definition of the MTTR in maintenance contracts is important so as to avoid confusion.

The lead time for parts that are not readily available or other Administrative or Logistic Downtime (ALDT) is not included in the calculation.