How Does a Conception Calendar Work?

A conception calendar can help a woman determine the best dates to attempt to conceive a pregnancy, or help an already pregnant woman determine the approximate date on which she conceived. Conception is the initial moment of pregnancy, at which point the sperm and egg join, according to Most women conceive within two days prior to, or on, the day of ovulation.

During the period just prior to ovulation, a woman is at her most fertile and is most likely to become pregnant, explains the American Pregnancy Association. Ovulation is when one of the woman's ovaries releases a mature egg, which then travels down the fallopian tubes towards the uterus so that fertilization can take place and the pregnancy begins. A fertilized egg implants in the woman's uterus within six to 12 days following ovulation. If fertilization does not take place within 12 to 24 hours, the egg disintegrates and exits the body with the woman's next menstrual period.

Doctors calculate a pregnant woman's due date from the first day of her last menstrual cycle, not the date of conception, says the American Pregnancy Association. Most women do not know the exact day of ovulation or conception but may be able to determine an approximate date based on their usual menstrual cycles.