--- title: "How to calculate MTBF and MTTR, with an example | attendo" description: "The MTBF and MTTR formulas with a complete worked example, the breakdown that changes the conversation and the three mistakes that make the number useless." url: "https://attendo.me/en/blog/how-to-calculate-mtbf-and-mttr" lang: "en" --- # How to calculate MTBF and MTTR without fooling yourself Both formulas fit on one line. The hard part is making the number mean something. Here are the formulas, a complete example and the three mistakes that turn these KPIs into decoration. - By the attendo team - Published September 27, 2026 - 4 min read **In this article** 1. The two formulas 2. A complete example 3. Mistake 1: calculating it on an incomplete history 4. Mistake 2: not deciding when the MTTR clock starts 5. Mistake 3: using it to compare different things 6. What to do with the numbers ## The two formulas ``` MTBF = operating time ÷ number of failures MTTR = total repair time ÷ number of repairs ``` **[MTBF](https://attendo.me/en/glossary/mtbf)** (mean time between failures) measures **reliability**: how long the equipment keeps running. **[MTTR](https://attendo.me/en/glossary/mttr)** (mean time to repair) measures **responsiveness**: how long it takes you to get it back into service. They are independent. One asset can rarely fail and take a week to repair. Another can fail often and be fixed in twenty minutes. ## A complete example Example Compressor `FRG-PLT1-CMP-002`, last 12 months. | Data | Value | | --- | --- | | Hours in the period | 8,760 h | | Downtime hours from failures, from failure to restart | 62 h | | Failures | 4 | ``` Operating time = 8,760 − 62 = 8,698 h MTBF = 8,698 ÷ 4 = 2,174.5 h (about 91 days) MTTR = 62 ÷ 4 = 15.5 h Availability = MTBF ÷ (MTBF + MTTR) = 99.3% ``` 99.3% sounds great. But it means 62 hours with the compressor down. If that facility keeps food cold, the useful question is not the percentage: it is what those 62 hours cost. Run the numbers with your own data MTBF, MTTR and availability Change the inputs and the result updates. The math runs in your browser: nothing is sent anywhere. ## Mistake 1: calculating it on an incomplete history It is the most common mistake and the most serious one. Say only 2 of those 4 failures were recorded, because two were fixed on the spot without opening a work order. The MTBF comes out twice as good as it really is. The KPI is only as good as the records behind it. Before you show an MTBF to anyone, ask whether every job is in the system. If the answer is “almost all of them,” the number is not good enough to base a decision on. ## Mistake 2: not deciding when the MTTR clock starts When the equipment fails? When someone reports it? When the technician arrives? An MTTR of 2 hours and another of 15 can describe the same service. The useful approach is to measure the whole time, from failure to restart, and **break it down**: | Stage | Hours | Share of total | | --- | --- | --- | | Detection and reporting | 8 | 13% | | Travel | 6 | 10% | | **Waiting for parts** | **36** | **58%** | | Actual repair | 12 | 19% | That breakdown changes the whole conversation. This asset’s problem is not the technicians: it is the parts room. Without the breakdown, the meeting would have been about productivity. ## Mistake 3: using it to compare different things MTBF only makes sense **within the same family** of equipment. Comparing a pump’s MTBF with an elevator’s tells you nothing. Where it does help is comparing an asset with itself over time, or twin assets with each other. If two identical compressors have an MTBF of 2,175 and 900 hours, something about the second one deserves a visit: the installation, how it is used or its environment. ## What to do with the numbers 1. **Rank your assets by MTBF** within each family. The bottom ten are your to-do list for the quarter. 2. **Cross MTBF with criticality.** An unreliable asset that is not critical is not a problem. An unreliable, critical one is urgent. 3. **Break down MTTR** and go after the biggest stage, which is rarely the repair itself. 4. **Watch the trend, not the single value.** A family whose MTBF drops three quarters in a row tells you more than any isolated figure. An MTBF calculated on incomplete records is worse than none at all, because it gives false confidence. Before you build the KPI, make sure every job goes into the system. That is the real work; the formula is the easy part. Last updated: September 27, 2026 ## How attendo handles it attendo CMMS calculates MTBF and MTTR by asset and by family from the work orders your team records. The same reports show plan compliance and cost per asset, and they can be emailed on a schedule. And technicians scan the QR code on the equipment to read its history before they start. - [attendo CMMS](https://attendo.me/en/cmms) - [Assets and inventory](https://attendo.me/en/modules/assets) - [CMMS software](https://attendo.me/en/l/cmms-software) ## More on maintenance ### The five maintenance KPIs that actually matter There are lists of thirty maintenance KPIs out there, and almost nobody uses thirty. These are five that change decisions, each with its trap, plus the ones you can usually drop. 4 min read ### Corrective vs. preventive maintenance: which one really costs more Everyone says preventive maintenance is cheaper, but few companies prove it with their own numbers. That is why it is the first thing dropped when an emergency hits. Here is the math, including the uncomfortable part: when corrective is the right call. 5 min read ### Asset inventory: where to start Every maintenance project starts with the inventory, and many get stuck there. Not because it is hard, but because it is tedious. And if it is done badly, everything that comes after inherits the problem. 3 min read [All blog articles](https://attendo.me/en/blog) ## Shall we look at it with your operation? Tell us how you work today and we will show you attendo with your own data. If it is not a fit, we will say so. - With your operation, not a generic demo - A real person from our team replies - No cold calls afterwards Would you rather talk first? - Phone [+34 910 053 530](tel:+34910053530) - Email [sales@attendo.me](mailto:sales@attendo.me) - Monday to Thursday 9:30 AM to 6:30 PM and Friday 9:30 AM to 2:30 PM (Spain time)