The Pearl Index compares methods of contraception. A high Pearl index stands for a high chance of unintentionally getting pregnant while a low value represents a low chance.
The Pearl index will be determined by the number of unintentional pregnancies related to 100 women. E.g. 100 women can us e a particular contraceptive for 1 year each with the method to be examined. If three pregnancies occur during this period in this group, the Pearl index will be 3.0.
To convert this abstract value to a concrete one, it is possible to multiply the Pearl index of a method by 0.4. The result is the number of pregnancies you will get in your life, if you use this particular contraception method during the whole of your fertile time (from 12 till 52 years of age).
Some examples of different birth control methods' Pearl indices:
| Pearl Index | |
| Knaus-Ogino | 15-35 |
| Cervical cap | 4-20 |
| Condom | 3-12 |
| Standard Days Method | 4-5 |
| Perimon | 1.3-3.8 |
| NuvaRing | 0.65-1.86 |
| Sympto-Thermal Method | 0.5-2 |
| Intrauterine Device IUD | 0.1-1.5 |
| Birth Control Pill | 0.1-1 |
| Sterilization | 0.1-0.4 |