Period-tracker apps are becoming ever more popular. While they have many benefits, worryingly more women are attempting to use these, usually free, apps to make decisions about contraception or to plan a pregnancy. Period-tracker apps will tell you when to expect your period, but they also often tell you which days they assume you are fertile, which day you could be ovulating, and even when they assume you are not fertile. Unfortunately this information is all generated within the app solely from the only information provided – your period start and end date.

This means period-tracker apps are essentially a digitized rhythm method or calendar method.

The rhythm method or calendar method assumes all women have the same cycle – that their cycle is usually the same length every month (approximately 28 days) and that they always ovulate at the mid-point of that cycle (around day 14). Period-tracker apps make the same assumptions for every woman who enters their period data. Within the first cycle the app will tell you when to expect your period and when to expect ovulation with no previous data recorded. As you enter more period data for your following cycles, the app will continue to assume you have a steady, unchanging cycle. The app may sometimes be right in its calculations, but it’s far more likely to be wrong the longer you use it. Although some women have very regular, consistent cycles and ovulation dates, many more do not. Period-tracker apps treat women like we are all the same and as though we are robot-like in our cycle experience.

As such, period-tracker apps can be very misleading – they can make you think your period is “late,” they can make you think you can have sex without a condom and not get pregnant, they can make you miss the days you need to be having sex if you do want to get pregnant. Unfortunately, many women don’t know this and trust these apps to handle everything for them, even believing these apps to be an effective birth control replacement. Period-tracker apps are just that, a way to track your period and provide approximate predictions for your next period.

How Daysy is different 

In contrast, Daysy is an intelligent computer that actually learns your unique cycle. She has a stored database of over a million clinically-studied cycles that are used for statistical analysis. Daysy has an integrated sensor that allows you to take your temperature every morning and she uses this data to understand your cycle. Using this data and your period data too, Daysy calculates and displays your fertility status for the day with a red, green or yellow light (red: fertile, green: non-fertile, yellow: learning phase/caution). Daysy takes your personal data and measures it against the data she has stored in her “brain” – allowing her to make smart analytical decisions about your cycle.

Daysy works by measuring, recording and analyzing your basal body temperature. This is the temperature of your body at rest – or your temperature when you wake up for the day. There are two predominate hormones involved in the fertility cycle, estrogen and progesterone. Estrogen is dominant during the pre-ovulatory phase (follicular phase) of your cycle, the time from the start of your menstruation until just before ovulation. Immediately after ovulation, during the luteal phase, production of the hormone progesterone increases and remains at an elevated level until just before the next menstruation. Progesterone causes the basal body temperature to shift by approximately 0.2 degrees Celsius. Daysy uses a complex algorithm to determine the change in average temperature values between pre-ovulation and post-ovulation. When the change is recognized, your Daysy knows that your ovulation has occurred and that you are no longer fertile.

Initially, when you first start using Daysy she determines your fertile window based on the statistical data she has in her computer database. Statistically speaking, women can ovulate as early as day 11 of their cycle, so Daysy begins her “red” (fertile) days around day 6 or 7 depending on the length of your menstruation. The red days will continue until Daysy has been able to confirm you have ovulated. In the beginning, Daysy is very cautious and it could take up to 5 or 6 days for Daysy to be certain that the temperature shift was in fact due to ovulation and not some other factor (i.e. the time you took your temperature, a fever, alcohol consumption the night prior…).

Over the course of the first few cycles, as Daysy learns your unique fertility cycle, she will slowly and cautiously reduce the number of red days she gives you. Daysy will begin to pinpoint your ovulation and start your fertile window (the red days) to 5 days before your earliest ovulation. The fertile phase will then continue until ovulation has been confirmed. So if you are a woman who generally ovulates around day 15-17 of your cycle, you will see that Daysy slowly moves the start of your red days back to day 10. Daysy always starts your fertile window 5 days before your earliest ovulation in the past 20 cycles. This accounts for the length of time that sperm can survive inside the female body (up to 120 hours) and protects those with irregular cycles. Daysy will monitor your temperature data and use her proprietary algorithm to compare the average temperature prior to ovulation compared to the average temperature after ovulation to determine when ovulation actually occurred.

This is why Daysy goes through a learning phase and gives most users a high number of red days for the first several cycles. The fact that Daysy can actually look back at your previous cycles and use her complex algorithms to fully learn your unique fertility patterns is what sets her apart.

Generally, we say that the Daysy has a learning phase of three to four cycles. This does not mean, however, that you will not get any “green” lights during that time. Daysy will start out very conservatively and base your fertile window primarily on statistical data. Over the course of your next several cycles, Daysy will begin to weigh your data more heavily against the statistical data and slowly narrow down and give less red days as it is able to pinpoint your individual fertile window. Most women will end up with 9 or fewer red days per cycle.

This is why Daysy has a medically-certified accuracy rating of 99.3% for planning or preventing pregnancy. Daysy is a stand-alone device, but if you want to use an app because that’s what you are used to, you can download DaysyView. Then simply attach Daysy to your phone with the supplied cord and your data will come up on the app. There you can visually see your charts over each tracked cycle and monitor the timing of your coming period, your fertile window, and your ovulation day and know that it is information you can trust and rely upon.