Pearl Index Calculator

Your details

Total number of participants who were exposed to the contraceptive method during the study.
Total observation period in months. Multiply years by 12 to convert.
months
Number of unintended pregnancies that occurred during the study. Use method-failure pregnancies only for the perfect-use index.
Typical use includes pregnancies from user error; perfect use counts only failures when the method was used correctly every time.
Month-based uses 1200 = 12 months x 100. Cycle-based uses 1300 = 13 cycles x 100 (some publications use this for data collected per menstrual cycle).
If your study records exact woman-months of exposure (accounting for drop-outs), enter it here. Leave 0 to use women x duration instead.
Pearl IndexEffective
1

Pregnancies per 100 woman-years of exposure

Effectiveness tierEffective
Woman-years of exposure500
Annual pregnancy risk0%
Woman-months used6,000
1 pregnancies/100 WY
Highly effective<1Effective1-5Moderate5-15Less effective15+

Pearl Index: 1.00 - Effective

  • A Pearl Index of 1.00 means roughly 1.0 pregnancies per 100 women using this method for one full year.
  • This is comparable to combined oral contraceptives used under perfect conditions, or progestogen injections in typical use.
  • The study accumulated 500.0 woman-years of exposure across 5 unintended pregnancies (typical-use data).

Next stepThe Pearl Index assumes a constant failure rate over time, which tends to overstate risk for shorter studies. Life-table analysis is preferred for studies over 12 months.

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