Pearl Index


Of the Pearl Index indicates the safety of a contraceptive. Its value is predominantly calculated theoretically. Therefore, the details of the Pearl Index vary. Pill, for example, has a value between 0.1 and 0.9. The Pearl index "condom" is between two and twelve. How the metric is calculated and why higher values ​​speak for less security, you can read here.

Pearl Index: How is it calculated?

The Pearl Index was introduced in 1933 by the US biologist Raymond Pearl. It is a measure of how many of 100 women of childbearing potential will become pregnant within a year, despite using a certain method of contraception.

To calculate the Pearl index, Raymond Pearl created a formula containing one fixed and several variable values. The fixed component stands for 100 women who prevent a year with a certain method; He is also known as "100 Women's Years". You can specify it either in months (12 per year) or cycles (13 per year). For 100 women who prevent a year, either 1200 or 1300 results as a fixed value. The remaining factors include number of pregnancies, how many women were screened for the examination, and length of application time of the contraceptive method.

Calculation example: In one study, 140 women were screened for 24 months (equivalent to 36 cycles) using a specific method. Eight women became pregnant despite contraception within these 24 months. The formula for the Pearl Index is:

Number of pregnancies x 1200 (or 1300)
Pearl Index = ---------------------------------------------- -------------------------------------------------- ---

Number of women x number of application months (or cycles)

Accordingly, one calculates as follows:

8x1200 (or 1300)
Pearl Index = --------------------------------- = 2.9

140x24 (or 26)

The tested contraceptive method therefore has a Pearl index of 2.9. This means that at least two women become pregnant within a year despite this method of contraception.

Pearl index of the different contraceptive methods

In principle, the lower the Pearl Index, the safer the method. Currently the safest contraceptive methods include hormonal contraceptives (oral contraceptives, pill) taken by mouth. For them, a Pearl index of 0.1 to 0.9 was calculated in various investigations. And how safe are condoms? Significantly less than the pill, they have a Pearl Index from two to twelve. Below are the Pearl indices of various contraceptive methods:

progestin implant

0 to 0.8

Sterilization of the man (vasectomy)

0.1 to 0.15

Micropille (estrogen, progestin)

0.1 to 0.9

Estrogen-free pill


Sterilization of the woman (tube sterilization)

0.2 to 0.5

Progestin depot injection

0.4 to 1.4

Mini-pill (progestogen only)

0.5 to 3.0

vaginal ring


hormone patches



0.9 to 3.0


2 to 12

temperature measurement


coitus interruptus

4 to 18

cervical Cap


Natural family planning with time selection method



12 to 20

No contraception

85 to 90