MTTR Calculator
Work out the mean time to repair from your own incident data.
In short
Formula: MTTR = Total repair time / Number of incidents repaired
What this calculator does
The mean repair time defined in the NIST/SEMATECH handbook. It is a mean, not a median: a single long incident moves it.
Use it to turn Total time spent restoring service, Incidents repaired into a checked result you can compare, copy, or rerun with different assumptions.
The page shows the formula, a numeric worked example, and the assumptions that affect this professional & industry calculation.
Inputs and what they mean
- Total time spent restoring service
- — Sum of the restore times of every incident in the period..
- Incidents repaired
- — Number of incidents those hours cover..
How to use it
- Enter your own figures — the calculator never fills in a rate, price or benchmark for you.
- Press Calculate to see the result.
- Read the formula, variables, assumptions and source below the result before you rely on it.
Formula
MTTR = Total repair time / Number of incidents repaired.
Inputs used: Total time spent restoring service, Incidents repaired.
Edge handling: Total time spent restoring service is required.; Total time spent restoring service cannot be negative.; Total time spent restoring service must be no more than 1000000000000.; Incidents repaired is required.; Incidents repaired cannot be negative..
Worked example
18.5 hours of restore work across 7 incidents
- Start with Total time spent restoring service: 18.5, Incidents repaired: 7.
- Apply the method: MTTR = Total repair time / Number of incidents repaired.
- A mean over the incidents you counted. It is not a target repair time.
Reading the result
The headline figure is the main answer. Any breakdown underneath shows the parts that make it up, so you can check the working and see what changes when you adjust an input.
Limitations and assumptions
- Inputs outside the supported range are rejected rather than forced into a result.
- The result depends on the values you enter for this mttr calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.
Reference: National Institute of Standards and Technology — Reliability measures: MTBF, MTTR and availability
Last reviewed:
Common questions
Where does this formula come from?
Section 8.1.2.4 — mean time between failures is operating time divided by the number of failures; mean time to repair is total repair time divided by the number of repairs; inherent availability is MTBF / (MTBF + MTTR). See the source link on this page.
What kind of calculation is this?
The arithmetic mean of the restore times of the incidents counted. Check the formula, example, and limitations on this page before using the result for a real professional & industry decision.
What are its limits?
Arithmetic over the figures entered — it cannot tell whether the underlying monitoring, incident records or change records are complete. A mean over a short period, or over few events, is a weak description of behaviour. A mean hides the spread; a median or percentile answers a different question and is not calculated here.
How do I use the MTTR Calculator?
Enter the required values for Total time spent restoring service, Incidents repaired. The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.
What formula does the MTTR Calculator use?
MTTR = Total repair time / Number of incidents repaired The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone. Check the formula, example, and limitations on this page before using the result for a real professional & industry decision.
Can the MTTR Calculator be used for exact decisions?
Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.
Formula, source and verification
The arithmetic mean of the restore times of the incidents counted.
The question it answers: What availability, uptime, mean time between failures and mean time to repair does our own data show?
The formula
MTTR = Total repair time / Number of incidents repaired
- Tr — Total repair time
- (h). Sum of the restore times in the period.
- n — Incidents
- (count). Number of incidents those hours cover.
Units: Hours in, hours and minutes out.
What kind of calculation this is
Deterministic formula. The same inputs always give the same answer. The maths is fixed and does not depend on judgement.
Method
The mean repair time defined in the NIST/SEMATECH handbook. It is a mean, not a median: a single long incident moves it.
Assumptions built into the result
- Mathematical: The figures entered all cover the same measurement period.
- Mathematical: Incidents, changes and requests are counted consistently with the definition the team has written down.
- Mathematical: Every incident counted has a recorded start of impact and a recorded restore time.
Figures this calculator will never guess for you
- No target, benchmark, industry average or performance band is supplied for any figure.
- A definition is never presented as a goal: the availability formula is not an availability target, and the change failure rate formula is not an acceptable failure rate.
- No target repair time is stated or implied.
Limitations
- Arithmetic over the figures entered — it cannot tell whether the underlying monitoring, incident records or change records are complete.
- A mean over a short period, or over few events, is a weak description of behaviour.
- A mean hides the spread; a median or percentile answers a different question and is not calculated here.
Source and version
- Standard or reference
- NIST/SEMATECH e-Handbook of Statistical Methods — NIST (Section 8.1.2.4 — mean time between failures is operating time divided by the number of failures; mean time to repair is total repair time divided by the number of repairs; inherent availability is MTBF / (MTBF + MTTR).)
- Published source
- National Institute of Standards and Technology — Section 1.4
- Formula version
- Version 1
- Verification
- Reviewed against the cited source on
- How much weight the source carries
- Standards or government
- Applies to
- Currency
- The result is a ratio or index, so it does not depend on currency.
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