Pearl Index (Contraceptive Failure Rate)
Pearl Index: (accidental pregnancies x 1200) / total woman-months of exposure = contraceptive failures per 100 woman-years; a lower index reflects a more effective method.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Accidental pregnancies
- 2
- Total months of exposure
- 1200 months
Result: Pearl index 2 per 100 woman-years — lower = more effective.
The tool opens with these values already filled in. Replace them with your own.
What the result means
- per 100 woman-years
- (accidental pregnancies x 1200) / months of exposure. Lower = more effective contraceptive method. A failure rate, not a diagnosis.
What you enter
- Accidental pregnancies
- Total months of exposure
How this is calculated
Pearl R. Factors in human fertility and their statistical evaluation. Lancet. 1933;222(5741):607-611. (Pearl Index.) Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.