By: 12 July 2017
Many fertility apps are misleading women by providing inaccurate estimates of ovulation day

A study presented in July at the ESHRE (European Society of Human Reproduction and Embryology) annual meeting reports that women with a standard cycle length of 28 days only have a 14 per cent probability of ovulating on day 14 (the historically assumed day of ovulation). This calls into question the usability of many fertility apps, which are based on this historic assumption. 

There are almost 100 menstrual cycle tracking apps available to women to provide them with predictions of their fertile days; the most popular report over one million downloads.[2] These apps, particularly those that are free, typically use the calendar method to predict the day of ovulation, despite the previously well-documented inaccuracy of this method.[3,4] New data, from a study specifically looking at the cycles of women who are actively seeking to conceive, demonstrate that many fertility apps using historic cycle-length data are providing women with inaccurate information on when to time intercourse.[1] Therefore, they may actually be hindering, rather than helping, women to become pregnant.

“This new study supports what many of us see in practice, that there is significant variability in cycle length and ovulation day between different women and also between cycles for individual woman” commented Bill Ledger, Professor of Obstetrics & Gynaecology in the School of Women’s & Children’s Health, Sydney, Australia. Professor Ledger went on to highlight, “Most apps use studies of the general population to identify the likely date of ovulation. These studies may not be applicable to the population seeking to conceive. This group tend to be older and may include a higher incidence of irregular ovulation and subfertility.”

The study, conducted by researchers from SPD Development Company (manufactures of Clearblue®pregnancy and ovulation test), at the Clearblue Innovation Centre in Bedford in the UK, evaluated the day of ovulation in 850 volunteer women (>18 years) from the UK who were seeking to conceive. Women collected daily urine samples for one full menstrual cycle which were analysed to detect a surge in luteinising hormone (a recognised biochemical marker for predicting ovulation).[1] Of these women, only 34 per cent had a 28-day cycle, in which day 16 had the highest probability of being the day of ovulation rather than day 14 (21 per cent compared with 14 per cent). Interestingly, a broad spread of probable ovulation days was observed from day 11 to day 20. A similar pattern was also seen in cycle lengths that were both shorter and longer than 28 days.

Dr Sarah Johnson, Head of Clinical and Regulatory Affairs from SPD Development Company, highlighted:These data are exciting, as whilst menstrual cycle characteristics are well established, we are able to demonstrate the enormous variability that exists in ovulation days between women, even those with the same cycle length, calling to question the validity of many of the smartphone apps that have become part of daily life for scores of women seeking to conceive”.


  1. Johnson S., Marriott L. Inaccuracy of the calendar/App based methods for predicting day of ovulation in women who are actively trying to conceive. Presented at ESHRE. July 2017: Geneva (abstract no. O-204)
  2. Duane M.,et al. The Performance of Fertility Awareness-based Method Apps Marketed to Avoid Pregnancy. J Am Board Fam Med (2016) 29: 508–511.
  3. Zinaman M.,et al. Accuracy of perception of ovulation day in women trying to conceive. Curr Med Res Opin (2012) 28: 749–754.
  4. Fehring RJ.,et al. Variability in the phases of the menstrual cycle. J Obstet Gynecol Neonatal Nurs (2006) 35: 376–384.