The Science Behind Daysy
Fertility tracking usually gets
explained with estimates
and assumptions
Let us introduce you to the
biological signal Daysy is built on
and why it's used.
- The biological signal
Yes, it's time for the
science bit
Your body gives you a lot of signals across the month.
Your body gives you a lot of signals across the month.
One of the most reliable is your basal body temperature (BBT) - the temperature you have first thing in the morning before moving, eating, or drinking.
Hormones shift your temperature in a predictable way:
• Before ovulation, estrogen keeps your temperature lower
• After ovulation, progesterone raises it slightly
Daysy reads these small shifts to help you understand where you are in your cycle.
- Temperature across a cycle
What it looks like
Before Ovulation
Lower temperatures
During Ovulation
A transition period as
hormones shift
After Ovulation
Higher temperatures
The changes are very small, often just a few tenths of a
degree, which is why Daysy is built to measure temperature
with medical-grade precision.
The changes are very small, often just a few tenths of a degree, which is why Daysy is built to measure temperature with medical-grade precision.
What Daysy measures (and what it doesn't)
Daysy focuses on your morning temperature
and the pattern it forms over time.
That's enough to classify your fertile
and non-fertile days with a high level of accuracy.
The algorithm
How Daysy's algorithm works
01
Data Input
Daysy measures your basal body temperature with 0.01 °C precision, collecting accurate readings over time.
02
Pattern analysis
The algorithm analyses how your temperature changes across days, focusing on patterns rather than single readings.
03
Day classification
By identifying post-ovulatory temperature shifts, each day is classified as fertile, possibly fertile, or not fertile.
04
Clinical Validation
This approach is supported by a peer-reviewed study of 5,328 users and over 100,000 cycles, where Daysy identified non-fertile days with 99.4% accuracy
-
99.4 % accuracy
-
Clinically validated
-
Hormone free
-
Used by over 250K women worldwide
-
2 year warranty
-
30-day risk-free return
How it works
60 seconds and
you're done!
Here's the simple version of how it works
01
You take a 60-second temperature reading each morning
02
Daysy updates your pattern automatically
03
It classifies your day as fertile, possibly fertile, or not fertile
04
The lights show you the result - red, yellow, or green
Over time, Daysy learns your unique
rhythm, and your results become
more personalized
- Trusted by 250,000+ women worldwide
Daysy is making their
lives easier
-
“I'm very satisfied. Have been using the Daysy for almost a year and she keeps her promise. Eventually you get used to the morning measurement... everything is better than swallowing hormones.”
Verified buyer
-
“I've been using Daysy for two years now and absolutely love it!! It's so easy to use... Daysy has been super accurate with everything so I confidently use it...”
Verified buyer
-
“Give yourself the time of day to learn the tool — it's just a small commitment (1–2 minutes) every morning and the insights are life changing.”
Verified buyer
- Why temperature matters
Why temperature?
But your body isn't average.
Why temperature matters
Why temperature?
Other methods predict fertile windows by estimating based on generic averages of past cycles.
But your body isn't average.
Daysy uses what your body did this morning, not what an app thinks might happen.
This helps create a clearer, less confusing picture over time. Especially if:
- Your cycle varies
- You've tried apps that contradict each other
- You want a hormone-free method
- You prefer something simple and quick
- A simple routine
A quick check in the morning, a clearer picture over time
Understanding your cycle shouldn't take over your day.
Daysy is built to be a small, steady routine that becomes clearer with time.
Most people take their reading in under a minute, then get on with their morning.
After a couple of cycles, the "learning days" decrease and the pattern becomes clearer.
A simple routine
A quick check in the morning, a clearer picture over time
Understanding your cycle shouldn't take over your day.
Daysy is built to be a small, steady routine that becomes clearer with time.
Most people take their reading in under a minute, then get on with their morning.
After a couple of cycles, the "learning days" decrease and the pattern becomes clearer.
