Chapter 5 – Managing the Test Activities
Mean Time To Failure (MTTF) – ISTQB Definition
Last Updated: July 12, 2026 · SoftwareTestPilot QA Team
Official ISTQB Definition
The arithmetic mean of the time between observed failures of a system.
In simple words
On average, how long the system runs before it fails.
Exam tip
MTTF is for non-repairable systems; MTBF is for repairable ones.
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