Definition
MTBF (Mean Time Between Failures) is the average length of time a system operates correctly between consecutive failures. A higher MTBF means failures are rare and the service runs a long time before breaking.
Where MTTR measures recovery speed, MTBF measures stability — how often things go wrong. Together they paint a complete reliability picture: you want a high MTBF (rare failures) and a low MTTR (fast recovery).
Why It Matters
MTBF tells you whether your reliability problem is frequency or duration. A low MTBF means you're failing often and should invest in root-cause fixes and resilience. Tracking it over time shows whether engineering work is actually making the service more stable.
How It Works
MTBF = total operational (up) time ÷ number of failures over a period. If a service ran 720 hours in a month and failed 4 times, MTBF is 180 hours. It's calculated from the same incident records used for uptime and MTTR, just measuring the gaps between outages instead of their length.
Real-World Example
In a 30-day month (720 hours) a service has 3 outages. Total uptime is roughly 719 hours. MTBF ≈ 719 ÷ 3 ≈ 240 hours — meaning, on average, about 10 days of normal operation between failures.
Best Practices
- Track MTBF alongside MTTR for a full reliability picture
- Investigate root causes to push failure frequency down
- Watch MTBF trends over time, not single-period values
- Build redundancy for components that fail most often
- Use accurate incident records as the basis for the calculation
Common Mistakes
- Looking at MTBF in isolation without MTTR
- Calculating MTBF from too few incidents to be meaningful
- Ignoring near-misses that signal rising failure risk
- Treating MTBF as a guarantee rather than a historical average
- Not addressing the recurring root causes that lower MTBF
In Monitoristic
Monitoristic's incident history gives you the failure timestamps needed to calculate MTBF over any period. Combine it with the uptime percentage and MTTR from the same timeline to understand both how often and how long you go down.