Bathtub Curve Failure Rate Calculator

Work out bathtub curve failure rate instantly with clear inputs, formula shown and shareable results.

About Bathtub Curve Failure Rate Calculator

The bathtub curve has three regimes. Infant mortality shows a falling hazard rate, modelled with a Weibull shape near 0.5 and addressed by burn-in and better process control. Useful life has a constant rate. Wear-out has a rising rate, shape 3 or more, and is addressed by scheduled replacement.

Formula

Phase hazard rate

h(t) = base rate x (age / design life)^(beta - 1) with beta 0.5 infant, 1 useful life, 3 wear-out

Worked example

With the default values below, Bathtub Curve Failure Rate Calculator returns Current Failure Rate of 250.0000. Change any input above and every figure here is recalculated in your browser.

Inputs used

Life Phaseone of Infant mortality (decreasing), Useful life (constant), Wear-out (increasing): Useful life (constant)
Base Failure Rateminimum 0.001 failures per million hours: 250 failures per million hours
Current Ageminimum 0.01 hours: 6,000 hours
Design Lifeminimum 0.01 hours: 20,000 hours

Results

Current Failure Rate: 250.0000
Implied MTBF: 4,000.0
Weibull Shape Assumed: 1.00
Survival To Current Age: 22.313%

Step by step

1Values used
2Phase hazard rate
3Current Failure Rate= 250.0000
4Implied MTBF= 4,000.0
5Weibull Shape Assumed= 1.00
6Survival To Current Age= 22.313

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How do I know which phase an asset is in?

Plot cumulative failures against age. A concave curve means infant mortality, a straight line means constant rate, a convex curve means wear-out has begun.

Does preventive replacement help in every phase?

No. It helps only in wear-out. Replacing components during infant mortality actively increases failures, because a new part restarts the high-hazard period.