Daysy Fertility Tracker


Daysy is a fertility tracker that uses the temperature method. It uses a unique algorithm that learns and tracks your cycle and displays your fertility in a color system [red = fertile, yellow = learning,green = infertile] Daysy is all natural, free of side effects and no charting is necessary.
Every morning when you wake up, you measure your temperature under your tongue. Enter if you have your menstruation then Daysy will evaluate your data and shows you if you are fertile or not.

Daysy has provided a special discount for our community:
For American & International Wonderful Within readers Get $15 Off at
For European wonderful within readers Get €10 off at

Additional information

I have reviewed the Daysy fertility tracker on the blog ‘My Honest Experience Using Daysy as Birth Control’I hope that by sharing my experience and perspective it was helpful for you in making a choice!

Daysy claims to be 99.4% accurate with perfect use*

Scientific Studies
The algorithm used in daysy is based on that used by the devices from Valley Electronics GmbH, which have been tracked by over 28 years of use.

It’s important to note that an initial study in 2016 was pulled from the reproductive health journal for selectively using data that made it look good — and undercounting possible unintended pregnancies.

*A follow up study was conducted in 2021 ‘The Performance of a Fertility Tracking Device [Roemer 2021]’ A total of 0.6% of all displayed green (infertile) days by the Fertility Algorithm were identified as false positives. Therefore Vally Electronics (Daysy’s parent company) has stated an overall accuracy of 99.4%. However, the indipendant study discusses that “skipping [missed BBT recording] seems to have a direct effect on fertility identification” and concludes “further research is needed to explore the efficacy of the device in a prospective study.”


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