01
Collect Your Period Data
Pick an observation window (a month, a quarter, or a campaign run) and record the total scheduled operating hours, the number of unplanned failures, and the sum of all repair durations.
MTBF and MTTR Calculator
Mean time between failures, mean time to repair, and machine availability.
Updated Reviewed by Sajid Hussain· Editor
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Last updated
June 3, 2026
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9 markets · 8 currencies
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Reliability Engineering
What Are MTBF and MTTR?
MTBF (Mean Time Between Failures) and MTTR (Mean Time To Repair) are the two most widely used metrics in industrial reliability engineering. Together they tell you how often a machine breaks down and how quickly your team gets it running again — the two levers that directly control machine availability.
Machine availability is simply MTBF ÷ (MTBF + MTTR). A plant running at 95% availability loses 5% of its scheduled production time to unplanned stoppages. Knowing your MTBF and MTTR shows you exactly where to focus: fewer failures (raise MTBF with preventive maintenance) or faster recovery (reduce MTTR with better spares and training).
This calculator computes both metrics from your historical data, then gives you availability, failure rate per 1,000 hours, shift-level reliability, and the total cost of downtime in your period — so you can make a business case for investment in maintenance improvement.
Quick facts
- Excellent Availability
- ≥ 99%
- Good Availability
- 97 – 99%
- Fair Availability
- 95 – 97%
- Best-Practice MTTR
- < 4 hours
- Shift Reliability
- e^(−8 ÷ MTBF)
- Formulas
- IEC / ISO standard
How It Works
Four Steps to Your Reliability Numbers
02
Calculate MTBF and MTTR
The calculator divides total uptime hours by number of failures to get MTBF, and total downtime hours by number of failures to get MTTR. Both are expressed in hours.
03
Derive Availability and Reliability
Availability is MTBF ÷ (MTBF + MTTR). Shift Reliability uses an exponential model — e^(−8 ÷ MTBF) — to estimate the probability of completing an 8-hour shift without a stoppage.
04
Quantify the Cost and Act
Multiply total downtime hours by your cost-per-hour to see the financial impact. Then use the benchmark comparisons and smart warnings to decide whether to focus on failure prevention (MTBF) or repair speed (MTTR).
Steps to use the MTBF & MTTR Calculator: Collect Your Period Data, Calculate MTBF and MTTR, Derive Availability and Reliability, Quantify the Cost and Act.
Formulas
The Reliability Engineering Formulas
01
MTBF Formula
MTBF = (Total Operating Hours − Total Downtime Hours) ÷ Number of Failures
Numerator is total uptime (the machine was actually running). Denominator is the count of unplanned stops. Result is the average hours between each failure.
Example: (720 − 18) ÷ 6 = 702 ÷ 6 = 117.0 hours
02
MTTR Formula
MTTR = Total Downtime Hours ÷ Number of Failures
Divides total repair time across all failures by the number of failures. Result is the average time to get the machine running after each breakdown.
Example: 18 ÷ 6 = 3.0 hours per repair
03
Availability Formula
Availability = MTBF ÷ (MTBF + MTTR)
Availability is the fraction of time the machine is theoretically able to run. A machine with MTBF 117h and MTTR 3h is down 3 hours in every 120-hour cycle.
Example: 117 ÷ (117 + 3) = 117 ÷ 120 = 97.5%
04
Shift Reliability Formula
Reliability(t) = e^(−t ÷ MTBF)
Assumes an exponential failure distribution (constant hazard rate). For t = 8 hours (one shift), this gives the probability of zero failures during that shift.
Example: e^(−8 ÷ 117) = e^(−0.0684) ≈ 93.4%
Worked Example
Step-by-Step Walkthrough
Scenario
A production line runs 702 hours in a month (720 total, 18 downtime), with 6 unplanned failures. Downtime costs $500.00/hr.
1
Step 1 · MTBF
720 total hours − 18 downtime hours = 702 uptime hours. MTBF = 702 ÷ 6 failures = 117.0 hours per failure cycle.
MTBF = 117.0 hrs
2
Step 2 · MTTR
18 downtime hours ÷ 6 failures = 3.0 hours average repair
MTTR = 3.0 hrs
3
Step 3 · Availability
117.0 ÷ (117.0 + 3.0) = 117.0 ÷ 120 = 97.5%
Availability = 97.5%
4
Step 4 · Shift reliability
e^(−8 ÷ 117.0) = e^(−0.0684) = 93.4% chance of a full shift without failure
Shift Reliability = 93.4%
5
Step 5 · Downtime cost
18 downtime hours × $500.00/hr = $9,000.00 for the month
Total Cost = $9,000.00
The takeaway
Availability of 97.5% is good by industry standards. Reducing MTTR from 3.0 to 2 hours (faster spare-parts access) would lift availability to 98.3% and save roughly $2,700.00 per month at this cost rate.
Industry Benchmarks
Availability Benchmarks by Category
| Metric | Poor | Average | Good | Excellent |
|---|---|---|---|---|
| Machine Availability | < 95% | 95 – 97% | 97 – 99% | ≥ 99% |
| MTTR (Mean Time To Repair) | > 8 hours | 4 – 8 hours | 1 – 4 hours | < 1 hour |
| Shift Reliability (8 hrs) | < 85% | 85 – 92% | 92 – 97% | ≥ 97% |
| Failure Rate (per 1,000 hrs) | > 20 | 5 – 20 | 1 – 5 | < 1 |
Tool Comparison
Calcrux vs Manual Logs vs Paid CMMS
| Feature | Calcrux (Free) | Manual Log / Spreadsheet | UpKeep / Limble CMMS |
|---|---|---|---|
| MTBF & MTTR calculation | Manual formula | ||
| Availability benchmark comparison | |||
| Shift reliability probability | Add-on module | ||
| Downtime cost estimate | Manual | ||
| Smart warnings and insights | |||
| No login required | |||
| Cost | Free | Free | 200 – 2,000 per month |
Common Mistakes
Mistakes That Distort Your MTBF and MTTR
Including planned maintenance stops in downtime
Why it matters
MTBF and MTTR only measure unplanned failures. Mixing in scheduled maintenance inflates MTTR and suppresses MTBF, making reliability look worse than it is.
Fix
Record only unplanned stoppages. Track planned maintenance separately under preventive maintenance KPIs.
Using too short an observation window
Why it matters
With only 2–3 failures in the data, a single unusually long repair skews MTTR heavily. Averages need a statistically meaningful sample.
Fix
Use at least one calendar month of data, or a minimum of 10 failure events, before drawing conclusions from the averages.
Measuring clock time instead of operating time
Why it matters
A machine that runs one shift per day accumulates 8 operating hours per calendar day, not 24. Using calendar hours makes MTBF look 3× better than reality.
Fix
Log actual machine-running hours (from PLC, shift logs, or sensors) as your total operating hours input.
Confusing MTBF with MTTF for non-repairable parts
Why it matters
MTBF assumes you repair and reuse the same asset. For consumable parts (bearings, seals, belts) that are replaced, MTTF is the right metric — it measures life to permanent failure.
Fix
Use MTBF for the overall machine or a repairable sub-assembly. Switch to MTTF analysis for individual wear parts.
Treating MTBF as a guaranteed run-time
Why it matters
MTBF is a statistical average under the exponential failure assumption. It does not mean the machine will always run that long — 37% of the time it will fail before reaching the MTBF.
Fix
Use Shift Reliability (e^(−t ÷ MTBF)) to express the probability of failure-free operation for a specific duration rather than treating MTBF as a minimum guarantee.
Pro Tips
How to Improve MTBF and MTTR
Fix top 3 failure modes first
In most plants, 80% of downtime comes from 20% of failure modes. A simple Pareto of your failure log reveals which equipment or fault type to target for the biggest MTBF gain.
Pre-stage parts on-site
A large portion of MTTR is often waiting for parts. Keep a small strategic stock of the components that cause your longest stoppages. Even eliminating a 2-hour parts-chase per repair dramatically cuts MTTR.
Switch to condition-based maintenance
Vibration sensors, temperature monitors, and oil analysis can predict failures before they happen. Shifting from time-based to condition-based maintenance typically doubles or triples MTBF without increasing maintenance labor.
Document failure codes consistently
Reliable MTBF trends require clean data. Standardize fault codes in your log — "motor overload", "PLC fault", "seal leak" — so you can filter and compare by failure type across months.
Track MTBF monthly
A single period snapshot is a baseline, not a story. Track both metrics monthly on a run chart. A rising MTBF trend confirms that your maintenance improvements are working; a rising MTTR flags a resourcing or parts problem.
Use Cases
Who Uses the MTBF and MTTR Calculator
The MTBF & MTTR Calculator works across every stage of the workflow.
Maintenance Manager
Benchmarks the line against the 99% availability target, identifies that MTTR of 6 hours is the biggest gap, and makes the case to management for a spare-parts investment.
Reliability Engineer
Calculates MTBF before and after a PM schedule change to quantify improvement. Uses Shift Reliability to communicate failure probability in business terms to operations.
Plant Operations Director
Uses total downtime cost to compare the cost of current unplanned downtime against the annual cost of a predictive maintenance program, building the business case for investment.
Production Planner
Uses MTBF and Shift Reliability to add a realistic buffer into the production schedule for a high-failure machine, reducing missed delivery commitments.
Maintenance Technician
Tracks MTTR for their own repair jobs over time to benchmark personal response time and identify which repairs take longest — a basis for targeted skills training.
Glossary
Key Reliability Terms
Every important term you'll encounter in this calculator and the broader topic.
- MTBF (Mean Time Between Failures)
- The average operating time between consecutive unplanned failures on a repairable asset. Calculated as total uptime divided by number of failures. Higher MTBF = more reliable machine.
- MTTR (Mean Time To Repair)
- The average time from failure detection to full restoration of the machine to operating condition. Includes diagnosis, repair, and restart. Lower MTTR = faster recovery.
- Availability
- The fraction of scheduled time that a machine is theoretically ready to operate. Derived as MTBF ÷ (MTBF + MTTR). Industry benchmarks: excellent ≥ 99%, good 97–99%, fair 95–97%, poor < 95%.
- Reliability
- The probability that a machine will operate without failure for a specified duration. In this calculator, Shift Reliability is the probability of a failure-free 8-hour shift, computed using the exponential reliability function.
- Failure Rate
- The number of failures expected per unit of operating time — here expressed per 1,000 hours. Failure Rate = 1,000 ÷ MTBF. Lower is better. Also known as lambda (λ) in reliability engineering.
- Preventive Maintenance (PM)
- Scheduled maintenance performed at fixed intervals or based on usage to prevent failures before they occur. Effective PM programs raise MTBF and, if planned well, do not increase unplanned MTTR.
Help & answers
Frequently asked questions
Everything you need to know about how the MTBF & MTTR Calculator works.
01What is MTBF?
MTBF (Mean Time Between Failures) is the average operating time between two consecutive unplanned breakdowns. A higher MTBF means the machine runs longer before failing, indicating better reliability.
02What is MTTR?
MTTR (Mean Time To Repair) is the average time it takes to restore a machine after a failure. It covers detection, diagnosis, repair, and restart. A lower MTTR means your team recovers faster.
03How is machine availability calculated from MTBF and MTTR?
Availability = MTBF ÷ (MTBF + MTTR). If your MTBF is 117 hours and MTTR is 3 hours, availability = 117 ÷ 120 = 97.5%. This is the theoretical fraction of time the machine is ready to run.
04What is the difference between MTBF and MTTF?
MTBF applies to repairable systems and measures time between failures (the machine is fixed and reused). MTTF (Mean Time To Failure) applies to non-repairable items, measuring the expected lifespan before permanent failure.
05What is a good MTBF?
There is no universal answer — it depends on the machine type and industry. In general, higher is better. Use trends over time: if your MTBF is rising after a maintenance change, the change is working. Pair MTBF with availability benchmarks: 99%+ is excellent.
06What formulas does this calculator use?
MTBF = Uptime Hours ÷ Number of Failures. MTTR = Total Downtime Hours ÷ Number of Failures. Availability = MTBF ÷ (MTBF + MTTR). Shift Reliability = e^(−8 ÷ MTBF). These are standard IEC and ISO reliability engineering formulas.
07How can I reduce MTTR?
Keep critical spare parts on-site, create clear fault-isolation procedures, train technicians on the most common failure modes, and use remote diagnostics where possible. Even reducing average repair time by 30 minutes per event adds up quickly.
08What does Shift Reliability mean in this calculator?
Shift Reliability is the probability of completing a full 8-hour shift without a failure, calculated as e^(−8 ÷ MTBF). If your MTBF is 117 hours, Shift Reliability ≈ 93.4%, meaning roughly 1 in 15 shifts will see an unplanned stop.
09What are the limitations of MTBF and MTTR calculations?
MTBF assumes an exponential failure distribution, which suits random failures but not wear-out failures. Short observation periods give less reliable averages. Planned maintenance downtime should be excluded from MTTR. Always combine these metrics with RCM analysis for a full picture.
10Is this MTBF and MTTR calculator free and does it work globally?
Yes — completely free, no sign-up required, and calculated entirely in your browser. The formulas (IEC 60050-191 / ISO reliability standards) apply to any industry or country. Enter your cost per downtime hour in any currency and results convert automatically.
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Category
Manufacturing & ERP Operations
Subcategory
maintenance reliability
Availability
Global · 9 markets
Price
Free forever
Topics
MTBFMTTRmean time between failuresmean time to repairmachine availabilityreliabilitymaintenancedowntime cost
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