Could Your Fertility App Be Wrong?


Ovulation is the most important event of a woman’s menstrual cycle. Without it, pregnancy is not possible. Many patients, especially those with a diagnosis of unexplained infertility, rely on fertility websites and smartphone apps to help them nail down an ovulation time for BD (Baby Dance).

For years, I have been advocating for use of fertility apps along with BBT charts, cervical mucus monitoring, and OPK sticks to predict ovulation, never the app alone.

What we have noticed at Inner Peace is that frequently, the symptoms of ovulation do not match the predicted fertile window (Gasp!). For example, egg-white cervical mucus appears way before or way after the window. Let’s be real here, the algorithms each app uses for calculating ovulation date do not know how to check your cervical mucus for stretchiness.

Now there is data to support our theory.

Fertility App Study

Robert Setton, MD, from the Department of Obstetrics and Gynecology at Weill Cornell Medical College in New York City, and colleagues wrote an article published online on June 6 and in the July issue of Obstetrics & Gynecology. Their study of the top 20 fertility websites and 33 fertility smartphone apps found that 78.8% of apps and 75.0% of websites included days after ovulation as part of the fertile window, when there is little chance that conception will occur.

The study of course assumed a perfect 28-day cycle. Using the “gold standard”1 of ovulation calculation in the fertility world, the doctors predicted a five-day fertile window that was matched by one website and three apps. Some of the other apps predicted fertile windows starting as early as cycle day 4, and as late as cycle day 21.

Unfortunately, the study did not reveal names of the websites and apps studied.

Majority of women do not have a perfect 28-day cycle. Based on Dr. Setton’s study, it can be implied that with so much variation in actual cycles, the predicted fertile windows may be even more inaccurate even though the apps calibrate and recalculate each month based on data from the previous month,

This does not mean you should cancel subscriptions, boycott websites, or delete fertility apps from your phone.

How Fertility Apps Can Be Useful

The apps are useful in determining your cycle length. Most will display a cycle length history. It’s helpful to know this information to identify any alarming pattern. For instance, if your cycle is sometimes 24 days and sometimes 40 days, then it points to a possible estrogen imbalance.

Knowing the cycle length is also useful to calculate the length of the luteal phase. Luteal phase is the period of time after ovulation, aka the Two Week Wait. It rarely changes. A healthy luteal phase is 12-16 days in length. You can work backwards if you know the total cycle length to determine the ovulation date, and perhaps it will help you learn what the fertile signs were around that time.

Most apps have a BBT charting function built in, and even calculate a coverline for easy interpretation. If you dislike charting the old-fashioned way with a pencil and a paper chart, this could be a huge time saver. BBT charts are useful to confirm ovulation because your temperature should spike up to 98.0F or higher.  In Chinese medicine, energy imbalances internally have tremendous impact on basal body temperature. At Inner Peace, we dissect BBT charts down to how many days it takes for your temperature to spike after ovulation.  So if you are working with an acupuncturist, the information from your chart will provide valuable information.

The communities and forums on websites help to create a supportive environment during the process of trying to conceive (TTC). I always love forums because the reality is you are not alone.

There is never just one way of doing anything. I think most fertility websites and apps do work if you use them in conjunction with other tools and signs and symptoms to predict your fertile window.

  1. The study published that is considered the “gold standard” for calculating ovulation date can be found here 

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