What this calculator does
It solves a deterministic Duane cumulative-MTBF curve for the future test time at which the stated target intersects the modeled growth path.
When to use it
Use it for a first-pass test budget after a baseline point and a defensible growth slope have been established. It is not a reliability demonstration test, pass/fail sample-size calculation, or confidence-bound method.
Inputs and formula
Baseline time and baseline cumulative MTBF define one point on the curve. The target must be at least the baseline, and the improving growth slope must be between 0 and 1.
Target time = baseline time × (target MTBF ÷ baseline MTBF)^(1 ÷ β)Worked example and interpretation
At 100 test hours, a cumulative MTBF of 50 hours, target MTBF of 100 hours, and β of 0.5 produce 400 total test hours. That is 300 additional hours beyond the baseline point.
Practical notes and limitations
Small changes in β can create large changes in required time. Do not infer β from management intent. Re-plan when test profile, configuration, corrective-action effectiveness, or failure classification changes. Compare the result with available units, calendar utilization, and fix turn-around time.