07/31/2025 11:19 a.m.

Let a Fertility Monitor Calculate Your Fertile Days

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

Daysy will show you reliably when you can get pregnant

Do you want to get pregnant? Are you looking for a fertility monitor that determines your fertile days quickly and accurately?

Look no further than Daysy! Daysy is 100% natural and very accuarate! Determining when you are fertile is easy and comfortable with Daysy: Just take your temperature by measuring underneath your tongue before you get out of bed in the morning. If you are currently menstruating, confirm via the push of a button. That's it! You're done for the day. After only 60 seconds of measuring Daysy will flash a colorful light to show you if you are fertile.

A green light means no. A red light means yes – you are currently fertile / possibly fertile.

If you see a yellow light, it means that Daysy is still getting to know your cycle. And if you are currently ovulating, you will see a blinking red light. All clear? We told you it was easy!

Trying to get pregnant: Increase your chances

Why do some couples get lucky quickly and others have to wait for months to get pregnant? Physical reasons are rarely the cause for why couples are not getting pregnant.

The most important thing you can do to get pregnant as quickly as possible is to have sex at the right time. Only unprotected sex during a certain fertile window can get you pregnant.

This fertile window consists of only a handful of fertile days per cycle. So if you miss out on them, you have to wait for a whole cycle to get another chance.

The fertility monitor Daysy determines this window with precision: your fertile days during which sex can lead to a pregnancy. The right timing will significantly increase your chances for conception.

When am I fertile? Daysy's app will show you all there is to know!

If you are struggling to make time alone with your partner, Daysy can help you out with that too. It comes with an app that offers optimal planning support: install "DaysyDay" for free on your smartphone and synchronize it with Daysy fertility monitor.

Access your temperature curve and all your other cycle data and check out its best feature: the preview function that predicts next month's fertile window. This allows you to plan your free time around your cycle and make plenty of time alone with your partner on your fertile days.

In addition, you can share these data with your partner and allow him to earmark your fertile days ahead of time as well.

But the most important thing remains: Don't stress out. 

Much of this process is up to nature. Even if you regularly use a fertility monitor and time intercourse perfectly, it can still take months to get pregnant. Not every attempt at fertilizing an egg is successful, and not every successful fertilization leads to implantation. This is nature's way of selecting healthy embryos.

Trust your body, use the data to your advantage, and let Daysy handle the calculations.

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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Get more information

If you’re ready to start a family, read on to learn helpful tips to enhance your fertility and prepare for pregnancy.

The fertility tracker method is a modern, digital evolution of natural family planning. It eliminates common sources of error – ensuring ovulation is accurately detected and recorded.

Below, we’ll show you how traditional NFP (Natural Family Planning) rules differ from the features of modern fertility monitors – and how the two compare.