Certification and research confirm Daysy’s safety and quality:

Daysy - a medical product to rely on

Daysy has been developed as a medical product and registered accordingly with the CE mark. Not every cycle or fertility tracker on the market meets these standards. Unlike Daysy, not all were developed as medical products and are controlled by a quality management system. You can feel confident that Daysy’s safety and quality are our highest priority.


Daysy’s claim: certification, safety and quality

Valley Electronics AG, based in Switzerland, has developed Daysy, a medical product that focuses on the woman’s cycle and enables a better understanding of the female body. Valley Electronics AG is certified with EN ISO 13485:2016, meaning that our quality management is oriented toward the newest standards for medical products. As the customer, you are at the center of all decisions in product development and manufacturing regarding safety and risk. All procedures at Valley Electronics AG are regularly subjected to internal and external controls. This allows us to continuously enhance the quality of the product throughout its entire life cycle.


The Pearl Index

The effectiveness of each contraceptive method is based on the Pearl Index (PI), named after the American biologist Raymond Pearl (1879-1940). This index also applies to fertility tracker and is calculated from the number of pregnancies in 100 women in one year. For example: If one woman becomes pregnant in 100 women who use the same method for one year, the PI is 1.0. If two become pregnant, it is 2.0, and so forth. This means that the lower the PI, the safer the method. However, a distinction must be made between two values: The method related PI shows how well a method works when used without errors. The user-related PI, on the other hand, shows how this method typically proves itself in everyday life ("typical use").

Why do we use the Pearl Index?

The PI is repeatedly criticized as outdated and imprecise. Some things are not taken into account when calculating the PI; for example, the size of the group of women observed, their age, or the frequency of their sexual intercourse. In addition, many manufacturers of contraceptive products only quote the method-related PI in their studies, which refers to contraceptive safety without application errors. However, if you look at the safety of a typical related application, the PI value is completely different. This can be quite confusing. For example, the pill has a method related PI of 0.1 to 0.9. The range of the diaphragm is much larger. Here the PI ranges between 1 and 20, so one can justifiably ask which value is correct. Will 1 or 20 women out of 100 become unintentionally pregnant within one year? That's a huge difference. We give the PI for both method and user-related PI of the fertility tracker and App so you know exactly where you stand with your Daysy. Although Daysy is not a contraceptive, there is a very simple reason why we use the PI as a calculation method:Daysy must be comparable to other methods of controlled family planning.  For lack of alternatives, the PI is currently the most easily and widely understood for comparison purposes.

The Pearl Index by Daysy

Daysy has a method related PI of 0.6, so Daysy is 99.4% accurate in reporting your fertility statuses. Looking at the typical application, Daysy's unique combination of fertility tracker and app results in a PI of 1.3, which means that Daysy and DaysyView prove themselves particularly well in everyday life and provide a highly reliable indication of when you are fertile and when not. In this way, you can find out when the chances of pregnancy are greatest.

Daysy Clinical Study 2018.pdf (937.4 KB)


Important: Daysy is not a “contraceptive app” or “birth control computer.” Due to their certification, popular “contraceptive” apps advertise to be in the same class of medical product as the condom. According to directive 93/42/EWG, medical products that serve as birth control or protection from sexually transmittable diseases, such as the IUD or condom, are automatically assigned to class IIb. However, this classification gives no indication of the efficacy of a method of birth control. The classification only indicates the risk to the user’s health in terms of possible side-effects such as infections, intolerance, adhesions, thrombosis or the possible transmission of HIV. Since an app alone cannot prevent pregnancy or STDs, being named a contraceptive and thus placed in Class IIb is very misleading. Daysy indicates fertile and infertile days with 99.4% accuracy and completely side-effect free.


Clinical Research

Daysy is based on the same algorithm as the devices of its sister company, Valley Electronics GmbH, which have been evaluated and tested for more than 30 years. The method- and user-related safety of the algorithm has been previously tested in a clinical study resulting in a method-related Pearl-Index of 0.7 and a user-related Pearl-Index of 3.8 [Freundl et al., 1998].

The next clinical study followed in 2018 with the Women’s Clinic at the University Clinic Erlangen. The key question of the current study was whether the optional use of a mobile application (DaysyView App) as a display of the individual cycle could improve interest and thus the user-related safety. For the study, a total of 6278 Daysy users worldwide were contacted via email. The participants should answer questions about their individual cycle, experiences with contraceptives, pregnancy, the desire to have children and the use and acceptance of the app. A total of 4738 cycles were evaluated.

The results of the current study show that the method-related Pearl-Index has improved from 0.7 to 0.6, confirming the very high safety of Daysy and the integrated algorithm 20 years after the first study. If the user-related safety is examined, the Pearl-Index improves by more than half from 3.8 to 1.3.

The Pearl Index, also called the Pearl rate, is the most common technique used in clinical trials for reporting the effectiveness of a birth controlmethod. We used the Pearl Index in our study because this is the only available calculation to explain the effectiveness of a method even in fertility tracking. There is no other calculation out there so far for methods which are not per se a form of birth control. However, Daysy is not a contraceptive it shows you when you should use a contraceptive to not get pregnant. We believe that only a method like a condom, Diaphragm etc. are a form of contraception. Abstinence can be considered a form of contraception and that is why fertility awareness-based methods could be called a form of natural contraception.  

Daysy shows the fertile and infertile window with an accuracy of 99.4%. 

Daysy Clinical Study 2018.pdf (937.4 KB)

Daysy Clinical Study 2018 short version.pdf (81.7 KB)

Commentary on the content and background of the independent clinical study.pdf (109.8 KB)


Our research:

Retrospective clinical trial of contraceptive effectiveness of the electronic fertility indicator LadyComp/BabyComp.  [Freundl 1998]

  • Result: User-Related Pearl-Index 3.8
  • Method safety: Method-Related Pearl-Index 0.7

Improving usability and pregnancy rates of a fertility tracker by an additional mobile application: results of a retrospective efficacy study of Daysy and DaysyView App [Koch 2018]

  • 800 women took part in this international study.
  • The study was conducted and reviewed by 13 clinical gynecologists from three different universities.
  • A total of 4738 cycles were evaluated
  • Result:           
    • User-Related Pearl-Index 1.3
    • Method-Related Pearl-Index 0.6


How the algorithm behind Daysy works

The database within each device contains menstrual cycle data of women from real life scenarios. Many kinds of specific and diverse menstrual cycle scenarios have been integrated into the database over these 30 years, including menstrual cycles affected by stress, lack of sleep, alcohol and other factors. This data comes from our practical experience working with millions of women over three decades.

The algorithm is created by combining two elements - the acquisition and learning of new data (your daily basal body temperature, start and end of menstruation, accumulated past cycle data) and statistical methods (eg. the temperature rises after ovulation) that allow prediction of the coming cycle. In this way, it is possible to derive individual infertile (green) days and fertile (red) days after menstruation.

After a learning period, during which Daysy gathers your personal data, the algorithm begins to pinpoint your ovulation and start your fertile window 5 days before the earliest possible date of your ovulation. In order to determine an increase in temperature by the algorithm, a sustained characteristic temperature increase at the expected time of ovulation is required. If the algorithm has confidently recognized your ovulation, Daysy will show you subsequent individual infertile (green) days until the next menstruation.

In the background, the algorithm takes into account the previous average temperature for each measurement, so it is also possible to tolerate "outliers" or measurement failures. In order to not take any risks, Daysy will display yellow in the case of doubt and remember the event for the coming cycle -Daysy learns-.


A few degrees make the difference

In addition, Daysy uses a very sensitive sensor to measure the basal temperature. Its unique feature is that it waits for the mean temperature value, which can take between 30 and 60 seconds. The sensor warms up before it records your basal body temperature in order to receive a reliable result.

Daysy waits until the final temperature value has stabilized to complete the reading. If the temperature drops during the measurement (for example, due to cold air that gets into the mouth through breathing), the sensor waits for it to rise again and stabilize. This method ensures that the measurement is as precise as possible.


The difference between Daysy and common “contraceptive” apps

This much is for sure: An app can definitely not be used for birth control! It can merely display a status to its user and let them decide to use birth control or not. Therefore, even the term “contraceptive” for an app is misleading.

An important difference between Daysy and common contraceptive apps is that Daysy directly conveys the recorded data to the app, rather than requiring the user to manually input data. With other apps, the user is relying on a separate thermometer, which may not meet the necessary standards. This could result in inaccurate measurements and rounding errors, both by the thermometer itself or during manual input of the data into the app. These types of errors can lead to an unwanted pregnancy or the failure to get pregnant.

Daysy’s thermo-sensor is an integrated part of the fertility tracker. It is precisely adjusted to the algorithm and covered by the quality management system. Because Daysy does the measuring, recording, and evaluation of your temperature for you, rounding and input errors can be ruled out.

In order to appeal to customers, many common contraceptive or fertility tracking apps display a comparatively large amount of “infertile” days after menstruation, even in the first recorded cycle, and without knowing the next ovulation date. Daysy’s algorithm does not take this risk and requires 2-3 cycles to determine green (infertile) days, especially during the potential infertile phase after menstruation. This requires a little patience but pays off in safety.

Daysy is a one-time investment that comes with no additional costs and her companion app is free. Many other apps are based on memberships that appear reasonable at first, but in fact bear additional costs for items such as thermometers or hormone test kits.

This also reflects on the rate of how long an app is being used: According to the most recent study [Scherwitzl 2017], after a year, only 56% of women were still using their app. In our currently submitted study, 97% of Daysy fertility trackers are still in use after one year.


Daysy: we pursue safety, certification and quality all the way!

We want to offer even more than the current standard. That is why we continuously work to optimize Daysy. Needs and preferences can change during the daily use of Daysy, which is why we always strive to find the best solution for our users. To create and develop a world-class product, attention to detail is just as important as the big picture. In the future, we will continue to spare neither cost nor effort to make sure that you are always happy and safe with Daysy! Our mission is maximum safety and quality for you!


290.00 EUR

incl. VAT and Shipping

Daysy calculates your fertile and infertile phases with an accuracy of 99.4%.

Daysy calculates your fertile and infertile phases with an accuracy of 99.4%.

  • Fertility tracker Daysy (incl. battery)
  • Connection cable for your smartphone
  • Instructions for use

Product available - Delivery time: 3-5 days*