MTBF is how long a machine runs, on average, between breakdowns; MTTR is how long it stays down each time. A line with 500 planned hours a month and 20 breakdowns has an MTBF of 25 hours; at 45 minutes of repair plus 25 minutes waiting for someone to start, MTTR is 70 minutes, availability 95.3% and the loss about ₹2.52 lakh a year at ₹900/h. This calculator shows how much of that is pure waiting.
Last checked: 14 Oct 2026.
How the calculator works
Inputs:
- Planned production hours a month, after planned breaks and maintenance.
- Breakdowns a month, from the breakdown register, not memory.
- Average repair time (min): from the fitter starting work to good parts again.
- Average wait before repair starts (min): finding the maintenance person, a spare, an approval, the OEM engineer.
- Machine or line hour rate (₹/h); the OEE calculator explains why this is real money mainly on a bottleneck.
Formulas:
MTBF (h) = planned hours ÷ breakdowns
MTTR (min) = repair time + wait before repair
Downtime (h/month) = breakdowns × MTTR ÷ 60
Availability = (planned hours − downtime) ÷ planned hours
Breakdown cost per year = downtime × hour rate × 12
Waiting part of that cost per year = breakdowns × wait ÷ 60 × hour rate × 12
Two choices are deliberate. MTTR here includes the wait. A maintenance KPI reference gives MTTR as "total repair time / number of repairs" (checked 14 Oct 2026); many plants log only hands-on time there, but the production loss is the time to restore, so the calculator adds the wait and shows it separately. MTBF here divides planned hours, not the reference's "total operating time", so it reads about an hour high on the defaults; planned hours from the shift plan are easier to keep honest month to month.
Worked example (India)
One packing line or machining cell on three shifts: about 20 planned hours a day, 25 days a month. The inputs are assumptions (the calculator's defaults): 500 planned hours, 20 breakdowns, 45 minutes of repair, 25 minutes of waiting, ₹900/h.
| Result | Value | Working |
|---|---|---|
| MTBF | 25.0 h | 500 ÷ 20 |
| MTTR | 70 min | 45 + 25 |
| Downtime | 23.3 h/month | 20 × 70 ÷ 60 |
| Availability | 95.3% | (500 − 23.3) ÷ 500 |
| Breakdown cost per year | ₹2.52 lakh | 23.3 × ₹900 × 12 |
Strict MTBF on operating time is (500 − 23.3) ÷ 20 = 23.8 hours. The more useful split:
| Part of MTTR | Minutes per breakdown | Hours a month | ₹ a year at ₹900/h |
|---|---|---|---|
| Waiting before repair starts | 25 | 8.3 (20 × 25 ÷ 60) | ₹0.90 lakh |
| Active repair | 45 | 15.0 | ₹1.62 lakh |
| Total | 70 | 23.3 | ₹2.52 lakh |
More than a third of the downtime (25 of 70 minutes) is nobody working on the machine yet. A fixed call route to maintenance, the most-failed spares kept at the line and a rule on night-time purchase approvals cut it without new skills; halving the wait saves about ₹0.45 lakh a year here.
Two more Indian examples: a CNC machine and a sewing machine
Both columns are assumptions for illustration, not survey data.
| Input or result | CNC vertical machining centre | Single-needle sewing machine |
|---|---|---|
| Planned hours a month | 400 h (two shifts) | 208 h (26 days × 8 h) |
| Breakdowns a month | 8 | 12 |
| Repair time | 90 min | 10 min |
| Wait before repair starts | 60 min (OEM engineer or spare) | 15 min (line mechanic) |
| Hour rate | ₹1,200/h (machine hour rate) | ₹75/h operator only, or ₹3,000/h for a 40-operator line |
| MTBF | 50.0 h | 17.3 h |
| MTTR | 150 min | 25 min |
| Downtime | 20.0 h/month | 5.0 h/month |
| Availability | 95.0% | 97.6% |
| Breakdown cost a year | ₹2.88 lakh | ₹4,500 at ₹75/h; ₹1.80 lakh at ₹3,000/h |
| Waiting part a year | ₹1.15 lakh | ₹2,700 at ₹75/h; ₹1.08 lakh at ₹3,000/h |
The CNC: few, long breakdowns, 60 of 150 minutes spent waiting for an outside engineer or a spare. A service contract with a fixed response time, or two critical spares in stores, attacks the ₹1.15 lakh without touching the machine.
The sewing machine shows why the hour rate matters more than MTBF. At ₹75/h (assumed ₹600 a day all-in for 8 hours) a 25-minute stop looks trivial; on the operation that paces a 40-operator line, the same 5 hours a month are worth ₹1.80 lakh a year, and 15 of the 25 minutes are waiting for the mechanic.
What typical numbers look like
- There is no universal MTBF or MTTR target. The same KPI reference says MTBF has "no universal target, varies by asset class" and MTTR is "asset-class dependent" (checked 14 Oct 2026).
- Large plants still lose about a day a month. Siemens' True Cost of Downtime 2024 report says large plants average 25 downtime incidents and 27 hours of unplanned downtime a month (checked 14 Oct 2026), about 65 minutes per incident. It covers large automotive, FMCG, heavy-industry and oil and gas plants, and Siemens sells predictive maintenance: a direction, not a benchmark for a mid-size Indian plant.
- Indian figures. No public survey of MTBF or MTTR in Indian factories was found (checked 14 Oct 2026). Three months of your own honest breakdown register is the baseline to use.
What this number does not tell you
- Whether the hours could have been sold. The ₹ figure values every breakdown hour at the full rate: fair on the bottleneck or when sold out; on a machine that waits for the bottleneck anyway, much of it is not lost.
- Whether your log is complete. Stops under 10–15 minutes often never reach the register, so MTBF looks better and MTTR worse than reality.
- What a camera cannot see. A camera can show when a machine stopped, when someone arrived and when it cycled again: the wait-versus-repair split this calculator needs. It cannot see a fault inside a panel, why a part failed, or whether the first parts after restart were in tolerance.
Related guides
- Why Breakdowns Take So Long to Fix — and What a Camera Shows
- Where Your Sewing Minutes Go: The Non-Productive-Time Map
- Tracking Old CNCs Without a PLC: Logs vs Current Sensors vs Cameras (₹)
- What One Hour of Downtime Actually Costs an Indian Factory (₹)
FAQ
How do you calculate MTBF and MTTR? MTBF = planned (or operating) hours ÷ breakdowns; MTTR = average time from breakdown to production again. 500 hours and 20 breakdowns give an MTBF of 25 hours; 45 minutes of repair plus 25 of waiting give an MTTR of 70 minutes.
Should waiting time be included in MTTR? For the production loss, yes: the machine is down whether or not someone is repairing it. Mean time to restore includes the wait; many plants' mean time to repair does not. This calculator includes it and shows it separately.
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