📊 Pearl Index Calculator
Calculate the Pearl Index, the standard measure of contraceptive method failure rate per 100 woman-years of use.
What is the Pearl Index?
The Pearl Index, also called the Pearl rate, is a standard statistic used in clinical and epidemiological research to express how often a contraceptive method fails. It reports the number of unintended pregnancies that would be expected per 100 women using the method for one year.
How this calculator works
The formula is Pearl Index = (number of unintended pregnancies × 1,200) ÷ total months of exposure, where total months of exposure is the number of participants multiplied by the average number of months each one used the method. The factor of 1,200 converts the result to a rate per 100 women per 12-month year.
A lower Pearl Index means fewer failures relative to exposure time, and a higher Pearl Index means more failures. Reported Pearl Index values for different contraceptive methods commonly range from below 1 (most effective methods, used correctly) to over 20 (less effective methods, or typical/inconsistent use).
This calculator is for general educational and research-reference purposes only. Real-world Pearl Index figures reported in published studies also depend on the study population and correct-versus-typical use, so they should be interpreted alongside the original study methodology rather than compared directly across sources.