Pearl Contraceptive Index Calculator

Pearl Contraceptive Index Explanation and Clinical Context The Pearl Index is a commonly used measure of contraceptive effectiveness expressed as the number of unintended pregnancies occurring per 100 woman years of exposure. It is calculated by dividing the total number of pregnancies by the total woman years of exposure and then multiplying by 100. When exposure is reported in months the equivalent formula is pregnancies times 1200 divided by total months of exposure.

The index provides a simple summary metric for comparing contraceptive methods or study results but has limitations. The metric assumes a constant pregnancy hazard over time and is sensitive to how exposure is measured and reported. Short duration studies and small sample sizes can produce unstable estimates.

For more robust assessment of contraceptive failure rates consider life table analysis or cumulative probability estimates when individual level time to event data are available. Reference Hatcher RA, Trussell J, Nelson AL, Cates W, Kowal D, Policar M. Contraceptive Technology twenty first edition.

New York Columbia University Press. 2018.