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  • Dr. Singh, ND

Improving the Accuracy of Menstrual Cycle Tracking (Scientific Update)

Menstrual cycle tracking is an extremely valuable tool in developing "self-fertility awareness." It has been shown to help couples reduce the time to pregnancy by better predicting the "Fertile Window." The fertile window is a range of days in the menstrual cycle that have highest rates of pregnancy, assuming intercourse takes place during those days.

The Fertile Window usually starts about 5 days prior to ovulation, with the potential conception rate peaking about 2 days prior to ovulation, and then significantly decreasing at the end of the day that ovulation occurs.

There is a great deal of variance in menstrual regularity among Women, so current methods present potentially erroneous predictions for the exact ovulation day.

The Methods evaluated in Menstrual Cycle Tracking Ovulation from over 7043 Women and a total of over 60,000 recorded menstrual cycles are:

1. Ogino Method: this method assumes that the luteal phase (the phase immediately after ovulation until the end of the cycle) has a standard length of 14 days. Ovulation day is predicted as: total cycle length - 15 days.

2. Half-Cycle Method: this method assumes that ovulation occurs in the middle of the cycle. Ovulation day is predicted as total cycle length in days divided by 2. I.e. a 32 day cycle would imply that ovulation should occur on cycle day 16.

3. Optimized Method: this method tracks the length of the follicular phase (this is the period from cycle day 1 until ovulation) from previous cycle to predict the next cycles follicular phase length, and therefore the day of ovulation.

The data analyzed from over 60,000 recorded menstrual cycles demonstrated the following about the above methods:

  • The Ogino method seemed to be the less accurate about predicting ovulation day, especially when cycle length was above 32 days or less than 27 days. The assumption that the luteal phase is constant went against the presented data. Luteal phase lengths varied quite a bit.

  • The Half-cycle Method showed decreasing accuracy when the cycle length was less than 28 days.

  • The Optimized method had a similar accuracy as the Half-cycle method in the start, but as more data was available from previous cycles, the Optimized method showed greater accuracy. The analysis from the data showed that the length of the follicular phase is the strongest positively correlated variable when trying to determine cycle length and ovulation day. The length of previous follicular phases allowed for better prediction of the follicular phase of the next cycle and therefore a more accurate prediction for the ovulation day and fertile window.

The researchers concluded the the optimized method is the best calendar method to start with for couples trying to conceive, as it appears to provide the most accurate estimates for cycle length, ovulation day, and therefore the fertile window.

This article is in no way a replacement for medical advice or medical care, it is advised that anyone concerned about their Health should speak with their Naturopathic Doctor or Primary Care Provider.


1. Sohda, S., Suzuki, K., & Igari, I. (2017). Relationship Between the Menstrual Cycle and Timing of Ovulation Revealed by New Protocols: Analysis of Data from a Self-Tracking Health App. Journal of Medical Internet Research, 19(11).

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