Timed intercourse during the fertile window of the menstrual cycle is one of the main strategies employed by couples trying to conceive. We sought to assess the accuracy of websites and APPs by comparing the predicted fertile window of the top-resulting websites and APPs against the actual presumed fertile window in a regular 28-day cycle.
The top resulting websites and APPs that provide calendars for fertility and ovulation prediction were assessed. Cycles were standardized to 28 days in length, and the last menstrual period was set to January 1, 2015. The predicted date of ovulation and fertility window generated were compared to an actual estimated date of ovulation on Cycle Day (CD) 15, and a fertile window consisting of CD10–CD15.
Data from twenty websites and thirty-three APPs were collected. Of all the websites and APPs utilized, one website and three APPs predicted the precise fertile window. Ten websites and twenty-three APPs provided a predicted date of ovulation. Range of dates generated for fertility window were as early as CD5 and as late as CD21. CD14 was the only cycle day that was always included in the fertility window.
Electronic resources used by the public to predict fertile windows are generally inaccurate, though the clinical impact of this inaccuracy is unknown. While they all include the most fertile cycle day, the range of the fertility window varies widely. Patients who are trying to conceive with the assistance of electronic resources should be counseled on the inaccuracy of these modalities.