10/08/2025 8:53 a.m.

Daysy Your Ovulation Calculator for Easy Ovulation Detection

Dr. Niels van de Roemer
Dr. Niels van de Roemer Medical Adviser

Daysy your smart ovulation calculator for easy and accurate ovulation detection

If you’re trying to conceive and want a reliable way to predict your fertile days, the Daysy ovulation calculator is a highly accurate, science-based fertility tracker designed to help you identify your ovulation window with confidence.

Boost your natural chances of pregnancy with precise ovulation tracking

Do you want to have a baby and are looking for ways to boost your natural chances for a pregnancy? Then Daysy is just right for you! Daysy is a highly modern ovulation calculator that can calculate your fertile and infertile days with a high accuracy based on your morning basal body temperature (BBT). All you have to do is take your temperature underneath the tongue every morning before you get up. The measurement takes about 60 seconds. After that, Daysy might ask you to confirm that you are currently on your period. This too is done via the simple push of a button. Daysy then displays to you via a colourful light whether your are fertile or not.

A green light means that you are not fertile and it is highly unlikely for you to become pregnant. A yellow light means that Daysy still needs to get to know you a little better or that your cycle is slightly irregular. A red light means that you are currently fertile / possibly fertile and can become pregnant. Of course, Daysy also shows you when you are ovulating: In that case, the red light is blinking. To make the best use of your chances to become pregnant, you should have sexual intercourse with your partner on the red days, the day of your ovulation and also on the yellow days.

Perfect timing for couples trying to conceive

For many couples with an unfulfilled wish to have a baby, there are no physical reasons that prevent a pregnancy. Rather, it is an issue of the right timing. In our modern and fast-paced world, undisturbed time for two can be quite rare. Conflicting schedules, various free time activities and countless other commitments can let sex fall by the wayside. This can be quite frustrating, in particular when you want to have a baby but the timing is just never right. Daysy makes timing much easier, because you will know exactly when it makes sense to schedule time for romance.

To make it even easier for you, Daysy comes with an app for your smartphone: Daysys app "DaysyDay" displays your cycle calendar, your temperature curve and a practical preview of the next month. You can use this preview to schedule enough time with your partner during your upcoming fertile days.

Daysy ovulation tracker: easy and accurate

In order for you to be able to rely on Daysy as much as possible, five million female cycles were evaluated for Daysy's unique algorithm. For every measurement, Daysy works with the knowledge of this large database and can therefore display your fertile and infertile days. In addition to that, the ovulation calculator Daysy is equipped with a highly modern and extra sensitive test prod that enables very precise measuring and lets Daysy register even the smallest deviations in your basal body temperature.

Daysy ovulation calculator uses a medically validated algorithm based on over ten million menstrual cycles. This enables precise detection of:

  • Ovulation day

  • Fertile window

  • Infertile days

  • Cycle irregularities

Use Daysy not only to know when you are ovulating, but also to learn more about your cycle and your body. You will notice that with the ovulation calculator Daysy, you will feel much closer to your body and your femininity.

What is the best way to measure?

For optimal use of Daysy, we recommend that you should have slept sufficiently (at least one hour) before the measurement. It is important that you take your temperature immediately after waking up, before getting up and becoming active. Measure below your tongue, with your mouth closed, and keep the device steady while it is measuring. Video Tutorial

Do I have to measure at the same time every day?

No. You should have at least one hour of good quality sleep before the measurement. It is important that you take your temperature immediately after waking up, before getting up and becoming active. For optimal use of Daysy, try to get at least 3 or more hours of sleep before measuring. Less sleep can result in more temperature fluctuations causing Daysy to give more fertile or potentially fertile days.

How do I enter or edit menstruation?

You can confirm or remove menstruation at any time during the current day. Simply press the button to turn on your Daysy, and then press and hold the activation button until the violet light lights up without flashing and you hear a "beep." Confirm you are menstruating for each day of active bleeding and for a minimum of three consecutive days. You can also remove menstruation data for the same day by turning Daysy on and pressing and holding the activation button until the purple/blue light is no longer solidly lit and begins flashing again.

Video Tutorial

How long until Daysy knows my personal cycle?

The first 2-4 cycles of use are considered Daysy's learning phase. Over the course of her learning phase, Daysy will come to understand your cycle and begin narrowing down your fertile window. Daysy remains quite cautious and conservative during this time, which is why Daysy is accurate starting the very first day.

When can I start to rely on Daysy's results?

You can rely on Daysy's results starting the very first day of use. In the beginning, you will see more yellow and red days because Daysy is still learning your unique cycle. You will see more green days as Daysy comes to understand your cycle and can narrow down your fertile window. The more regularly you measure, the better.

My cycle is irregular. Can I still use the devices?

Yes. Irregular cycles are not a problem for Daysy/Lady-Comp. Even with irregular cycles, all Valley devices distinguish between non-fertile and fertile days with a very high accuracy. However, in case of extreme fluctuations between cycles it will give you more red and yellow lights and less green lights. Fluctuations of several days are usually not a problem. If you have questions about your unique cycle, please reach out to our team of experts.

Are there any costs associated with the DaysyDay app?

No! DaysyDay is free! There are no in-app purchases or upgrade fees.

Does illness reduce the reliability of the device?

In general, you should skip measurements during illness and while you are taking medication that can have an influence on your body temperature or cycle. If you have doubts, contact your doctor or our customer service team.

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