I’ve had Eve, a period tracker app on my phone for close to 6 years now, and for the longest time I had no idea how it worked.  All I knew is that it saved me the burden of having to remember details of my menstrual cycle, because if I’m being honest, that’s taxing. I’d rather use that memory space in my brain for something else. I began to deeply understand how period tracker apps work and the algorithm behind them and thought why not share it.

How period tracker apps work

Once you download any period tracker app, the first step is usually to enter dates of your previous periods, at least 3 months worth of dates. This step is important because the algorithm behind the app then identifies the trends in these dates to predict future cycles. It’s okay if you aren’t sure of the dates of your past 4- 5 periods, I know I can’t remember even the last month’s unless I check the app. If you can’t remember that far back, just enter the dates you are sure of and keep updating them as the months go by and in no time, your app will have enough data to predict your cycle. Before the app has enough data, it’ll estimate predictions based on the average cycle length, which is 28 days . It gets more personalized as a user enters her own data making predictions more personal. The more the data, the more the algorithm learns and the more accurate the predictions are.

Some apps, like Clue, allow you to enter your moods, sleep cycle, pain, and uses this data to not only predict your period but also ovulation and level of fertility all throughout the month.

Not always accurate

Unfortunately, these apps don’t have the menstrual cycle down to a science because the predictions aren’t as accurate as we’d want. There is always a window of plus or minus a few days or weeks from when the app predicts your next period. There are external variables that affect a woman’s cycle like her diet, even the weather, stress, change in environment, etc. The algorithms aren’t flexible enough to take into account these factors making predictions inaccurate many times, much to users’ frustrations.

All in all, I think using menstrual tracking apps is much better than using pen and paper because these apps can identify trends that you may not notice if you use your notebook.