How to Calculate Your Fertile Window

Getting pregnant is not as easy as having unprotected sex. Conception requires the sperm and egg to meet within a six-day period known as your ‘fertile window’. A man’s sperm is able to survive for up to five days following intercourse. However, a woman’s egg is only viable for 24 hours. Therefore, the probability of pregnancy rapidly declines at the end of the fertile window. The good news is that couples can use “fertility awareness” or “natural family planning” to significantly increase their odds of conception. By charting your fertility signs, you can calculate the best days to have sex.

Which Days Am I Most Fertile?

Your ‘fertile window’ is a period of six days consisting of the five days leading up to ovulation and the day of ovulation. Ovulation refers to the release of an egg which occurs just once a month. Once released, the egg travels down the fallopian tubes and into the uterus. If the egg is not fertilized within 24 hours it disintegrates and is shed with the lining of you uterus during your next period. 

The first day of your period is cycle day 1. Women with an average 28-day cycle will usually ovulate around cycle day 14. If a woman fails to get pregnant in a given month, her period begins which signals the start of a new cycle. While pregnancy is possible any time during your fertile window, the majority of pregnancies are contributed to intercourse that occurs within two days leading up to ovulation. 

What Signs Should I Look For?

By paying attention to your body, you can help determine where you are in your cycle. When charting, many women track their basal body temperature (BBT). Changes in hormones during a woman’s menstrual cycle cause her BBT to fall about 1 to 2 days before ovulation. Her BBT will then climb one to two days after ovulation. Another sign of fertility is increased cervical fluid, or cervical mucus (CM). As ovulation approaches, it’s common to have an increase in wet, clear, and stretchy CM.

How Does Fertility Charting Help?

Charting your fertility signs is an effective way to increase your odds of conception. If your cycles are irregular, you can better pinpoint ovulation by watching for signs like changes in BBT, CM, or by using an ovulation predictor kit which measure luteinizing hormone (LH) in your urine. As everyone’s fertility pattern is different, charting can help you determine which days you are most likely to conceive. 

Getting pregnant isn’t always easy. For young, fertile couples, chances of conception during the first three months of trying are between 20 and 37 percent. This number increases to 80 percent by one year and 90 percent after two years of trying. To maximize your chances of conception, it’s recommended that you have intercourse daily or at least every other day during your fertile window.