The Pearl Index and the effectiveness of contraceptive methods

To evaluate the various contraceptives based on their safety or efficacy, the Pearl Index is used as the standard. But what can this index tell us, how is it calculated and are these calculations really so reliable? We answer the most important questions about the Pearl Index.

What is the Pearl Index?

The Pearl Index seeks to assess the effectiveness of a contraceptive. Interpret the data collected for a specific contraceptive in such a way that you can show how many in 100 people have become pregnant despite using the contraceptive.

For example: the Pearl index of 2 means that 2 out of 100 women, despite the use of a specific contraceptive, became pregnant. There is also talk of a "failure rate" of 2%.

How is the Pearl Index calculated?

The lower the Pearl index, the higher the effectiveness of the contraceptive method. But how is the Pearl Index calculated? 

The calculation is based on 1200 months of use (100 women in one year) of a contraceptive. The index then notes how many of these 100 women became pregnant within a year using their respective contraceptive.

For example: the Pearl index of 2 means that 2 women out of 100 have become pregnant in a year. If Pearl's index is 0.05, one in 2000 women became pregnant within a year.

The Pearl Index (theoretical and practical)

Generally, the Pearl index is divided into two subgroups: the effectiveness of the method (the theoretical Pearl index) and the effectiveness of use (the practical Pearl index). 

While the effectiveness of the method is based on the assumption that the contraceptive method is used completely correctly, the effectiveness of its use gives us information on the typical and daily use of a contraceptive. Factors such as forgetting to take the pill, gastrointestinal upset or misuse are considered.

Pearl's index of hormonal contraceptive methods

The contraceptive method most used by women is the pill. About 31% of women in Germany take it and are convinced of its effectiveness. The Pill's Pearl Index is between 0.1 and 0.9 in most cases, which also makes it one of the safest methods of contraception.

Unfortunately, this efficacy comes at a high price, because the list of side effects is long. Weight gain, thrombosis, mood swings, chest tightness, migraines or nausea are just some of the possible side effects.

Pearl's index of natural contraceptive methods

How effective is trackle?

Natural Family Planning (NFP) gives up on hormones. Unfortunately, it is often believed that natural contraception is extremely expensive and unsafe or even requires surgery. However, these assumptions are wrong.


The most effective natural method is the symptothermal method on which trackle is based. The theoretical Pearl index of the symptothermal method is equal to 0.4 and therefore - just like the pill - is less than 1%.

The practical Pearl index of the symptothermal method, in which usage errors are also considered, is 1.8. To make a comparison: the practical Peal index of the pill is equal to 9.

Another advantage of trackle is that usage errors are reduced thanks to the digitization of the symptothermal method. Furthermore, implementation in daily life is much easier than manual evaluation with the thermometer and cycle sheet.

The Pearl Index: A Good Orientation

Considering the Pearl Index, this is a good way to compare contraceptive methods and their effectiveness and allows you to orient yourself in the variety of contraceptive methods and make a first choice. However, it is always advisable to keep this in mind: Regardless of the contraceptive method, only correct use can guarantee efficacy and reliability. Therefore, if you have any questions about contraception, ask your gynecologist and get detailed advice on finding the right method for you. If you have any questions about the use of trackle, write to us at - we can't wait to answer your questions.



Diedrich, K. et al.: Gynecology and obstetrics. 2nd Edition. Heidelberg. 2007
Frank-Herrmann, P. et al.: Natural family planning today. Modern cycle knowledge for advice and application, 6th edition. Heidelberg, 2020