Daysy - a medical product to rely on

Daysy has been developed as a medical product. 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 accuracy and quality are our highest priority.

Daysy’s claim: certification, accuracy 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 according to EN ISO 13485, 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.

Fertility Awareness Method

Fertility awareness-based methods (FABM) is a term that includes all family planning methods that are based on the identification of the fertile time. FABM methods depend on two key variables: first the accurate identification of the fertile days of a woman’s menstrual cycle (the fertile phase) and, second, the modification of sexual behavior either to plan a pregnancy or to use this knowledge to avoid pregnancy with a contraceptive method.

Daysy is a fertility tracker that uses the fertility awareness method by learning and tracking your menstrual cycle.

Daysy is a tool of FABM. We believe that these types of tools do not control contraception and should not be certified as such. Daysy rather uses quantitative data and statistical models based on this data to advise you to be aware of fertile days. Daysy distinguishes fertile from infertile days, allowing the user to make a decision to use a method of contraception, or not.


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 algorithm indicates fertile and infertile days with more than 99% accuracy and is completely side-effect free.

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 (e.g. 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 not be used for birth control! It can merely display a fertility status to its user and let them decide to use a contraceptive 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 when desired.

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.

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

Daysy: we pursue accuraty, 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 with Daysy! Our mission is maximum accuraty and quality for you!


Daysy is a fertility tracker that uses the fertility awareness method by learning and tracking your menstrual cycle.