Daysy and PCOS Can It Track Ovulation in Irregular Cycles

Basal body temperature reflects progesterone, a hormone that rises after ovulation.

This means:

• Temperature increases only after ovulation
• It confirms that ovulation actually occurred
• It works regardless of when ovulation happens

For example:

• Ovulation on day 14 produces a temperature shift
• Ovulation on day 35 produces the same type of shift

This makes basal body temperature one of the most reliable ways to detect ovulation in women with PCOS.

Basal body temperature is a direct reflection of progesterone. What Daysy reads is not an absolute temperature value, but the relative rise compared to each user's own pre-ovulatory baseline. That matters, because it means the algorithm works regardless of when ovulation happens.

For women with PCOS, continuous basal body temperature monitoring is particularly important. These women often have irregular and long cycles, which makes it difficult to know if and when ovulation has occurred. Many of our users with PCOS use Daysy to track the impact of lifestyle changes or therapies and supplementation on their cycle. The temperature chart is therefore much more than a fertility indicator: it's a window into what's happening inside your body.

Daysy communicates fertility status using a simple color system:

• Green means not fertile
• Red means fertile or possibly fertile
• Flashing red indicates predicted ovulation
• Yellow means uncertainty or learning phase

Daysy communicates through four colours. Green means you are not fertile. It can appear at the beginning of your cycle, during the pre-ovulatory phase when the likelihood of pregnancy is extremely low, and returns once ovulation has been confirmed, remaining until your next period begins. Solid red means you are fertile or possibly fertile. Flashing red indicates predicted ovulation. And yellow, the one that causes the most confusion, means the device is still learning your pattern, or that there's a cycle fluctuation that doesn't match what it has learned so far.

Yellow should always be read as potentially fertile. Always.

In a woman with regular cycles, after the initial learning phase, yellow days are relatively few. In a woman with PCOS and long or variable cycles, the picture may look different: there may be more red and yellow days, over a longer period, until ovulation is confirmed. This is not a flaw in the device. It is Daysy accurately representing what is happening in your cycle, where the window of potential fertility is genuinely longer and less predictable.

Daysy learns each user's unique cycle and calculates based on what is normal for her. If a 35-day cycle is regular for you, Daysy will not interpret that as irregularity. In an anovulatory cycle, Daysy makes this clear too: the lights stay red or yellow because there is no temperature rise to confirm ovulation.

When Daysy shows green, you can trust it. Our algorithm's accuracy in distinguishing between fertile and non-fertile days is 99.4%.

Daysy uses continuous basal body temperature tracking combined with an algorithm that learns your personal cycle pattern.

Instead of relying on fixed cycle lengths, it adapts to your body over time.

This makes it especially useful for:

• Irregular cycles
• Longer cycles
• Cycle variability

Many women across Europe and internationally use temperature-based tracking as a hormone-free way to understand their cycle.

What changes with PCOS

With PCOS, you may notice:

• More red and yellow days
• A longer fertile window
• Delayed confirmation of ovulation

This is not a flaw. It reflects the natural variability of the cycle.

Important guidance

Yellow days should always be considered potentially fertile.

Once Daysy confirms ovulation and shows green, you can rely on that result.