How accurate is the
Daysy fertility tracker?

Since inventing the world’s first fertility tracker in the mid-80’s, accuracy has always been our top priority.

Backed by 40 years of scientific research, we’re proud to bring you cycle predictions you can trust - whatever your family plans may be.

Your cycle, your choice

Your fertility isn’t a guessing game

We get it – switching to a natural method of family planning can feel like a risky move if you’re not trying to build your family just yet. Without the right tools, it’s normal to worry if you can rely on it.

We created these devices to provide women everywhere with a safe, hormone-free, and reliable alternative to traditional methods.

So you can easily use basal body temperature (BBT) to track your cycle and fertility stress-free - powered by one of the most accurate fertility tracking methods available today.

Our fertility trackers are

Registered medical devices

Supported by 17 clinical studies

Created by doctors and scientists

BBT IS THE MOST ACCURATE Method

How to track your cycle with basal body temperature

Basal Body Temperature (BBT) reflects your body's lowest resting temperature and is a key indicator of ovulation. Knowing these temperature shifts is the foundation of accurate ovulation tracking.

Typical BBT patterns:

  • Before ovulation (follicular phase): BBT is steady around 97.7ºF.

  • After ovulation: Rising progesterone causes a 0.4º–0.81ºF increase, staying elevated for 12–16 days.

  • If not pregnant: BBT drops with progesterone.

  • If pregnant: BBT stays elevated beyond 18 days.

Because changes are subtle, a high measurement accuarcy (to two decimal places) is essential. Standard wearables and basic thermometers simply aren’t precise enough.

BBT is the most accurate natural ovulation tracking method next to ultrasound.

Want to go deeper? Download our e-book on fertility tracking with BBT and learn all about it.

Get The E-Book
RELIABLE PREDICTIONS

Get daily predictions you can count on

After just 60 seconds of measuring your temperature, Daysy and Lady-Comp display your fertility status with a red (fertile) or green (not fertile) light. Yellow means that the device is learning about your cycle or there is more information needed and should be treated as fertile days.

  • Using your measurement data, the algorithm performs advanced statistical analyses to reliably predict your fertile window, or the 6 days per cycle when pregnancy is possible.

  • You’ll see this as red and green days on your Daysy, in your DaysyDay app or on the Lady-Comp display.

  • Even if you have an irregular sleep schedule, or the occasional higher temperature due to stress or travel, you can always rely on your device to give an accurate fertility prediction.

3 ways our devices ensure accuracy

Clinically validated algorithm based on millions of real cycles

Easy-to-use, medical-grade device that eliminates human error

Highly sensitive sensor with measurement precision up to 0.06°C (0.108°F)

Not all cycle trackers are created equal

Here’s what sets our devices apart

All-in-one fertility tracker

Other cycle trackers require a separate thermometer and app, which can lead to inaccuracies from thermometer calibration or manual transfer of data.

Valley devices take your temperature, store your data, and reliably calculate your fertility status in a single device.

The most sensitive sensor on the market

Unlike other basal body thermometers, ours record only your real - not extrapolated - temperature value to provide the most accurate reading.

If cold air enters your mouth during the measurement, the thermometer waits for your temp to stabilize, providing a reading to the 100th of a degree.

Registered medical device

Not every fertility tracker meets the standards for medical devices, which are subject to quality management and frequent regulatory inspections.

Medical Evaluation

The high measurement accuracy of the temperature sensors and the precise algorithm of the temperature calculation provide a high degree in method safety, which clearly stands out from competitive devices.
Dr. Andreas Marx
KEY SCIENTIFIC FINDINGS

Supported by decades of independent clinical research

99.4% accurate

Based on a 10-year analysis of 107,000 cycles, scientists confirmed that Valley’s algorithm distinguishes between non-fertile and fertile days with 99.4% accuracy.

See study
Detect ovulation with clinical reliability

Research presented at the International Meeting on Infertility and Assisted Reproductive Technology showed that Valley devices detect ovulation with similar results to ultrasound and hormone tests.

Studies
4.5 months average to conceive

A 3-year study with 686 women found that 81% of those who wanted to get pregnant were successful. Conception often happened in the very first cycle, and the average time to conceive was 4.5 months.

Pregnancy Planning
Hormone-Free

The results of a 2016 study involving 3,450 women indicate that our devices are recommended by gynecologists, particularly for women who wish or need to avoid hormonal methods.

Explore the summary of the study results
Meet The Family

Get a period tracker you can trust with your family plans

  • 500,000+ women worldwide trust our devices for natural family planning.
  • Take control of your body, your cycle, and your health.
  • Backed by science, our cycle trackers offer accuracy you can count on.

Join the community of confident women and experience the freedom of knowing your cycle — naturally and reliably.

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