Your Cycle De-Mystified

“How to Calculate Your Window of Fertility”

A typical menstrual cycle is 28 days long, with menstruation occurring on day 1. The day of ovulation, which normally occurs 12 to 16 days before the menstrual period begins, and the five days preceding ovulation are a woman’s most fertile time. So, for the average woman, the most fertile window of time is between days 10 and 17 of the menstrual cycle.

Problem - Most Women aren’t Average

Since most women aren’t average, it is necessary for you to pinpoint your own individual fertility window. One way to do this is to keep a record of your menstrual cycle for eight or more months, if possible. Then select your shortest cycle and subtract 18 from it. The resulting number is your first potentially fertile day. Then subtract 11 from your longest cycle. The resulting number marks your last potentially fertile day. So, for example, let’s assume that your cycles range from 27 days to 30 days over the time you recorded them. In this case, your first potentially fertile day would be found by 27 - 18, your shortest cycle minus 18, which gives you day 9. Your last potentially fertile day would be found by 30 - 11, your longest cycle minus 11, which gives you day 19. Thus, your fertility window is between day 9 and 19 of your menstrual cycle.

How to Narrow that Window of Fertility

You are probably thinking that day 9 to 19 is a large window of time, and you are correct. However, there is a way that you can narrow it. You must chart your basal body temperature (your morning temperature before getting out of bed). For most women, it ranges from 96 to 98 degrees Fahrenheit. When your temperature rises slightly (ie. 4/10 to 8/10 of a degree), it usually means you have ovulated within the past 12 to 24 hours.

One more method of identifying your fertile period is to notice changes in your cervical mucus. Cervical mucus comes in 3 varieties, dry or sticky or wet, stretchy, and semi-transparent. Dry cervical mucus usually occurs following menstruation. Sticky cervical mucus usually occurs approaching ovulation. Wet, stretchy, and semi-transparent cervical mucus usually occurs during ovulation. By noticing the stage your cervical mucus is in, you can also determine your window of fertility. Ovulation usually occurs from two days before to two days after the peak day of stretchy mucus.

Get Scientific About It

If you want some help determining your window of fertility, there are many products available on the market that do a good job of letting you know when you are ovulating. Check out the recommended products in our conception helpers section like the OV Watch or the Clear Blue Monitor.