You know your baby or child's birthday but what day did conception occur?

When was your baby was conceived? This conception calculator allows you to calculate the exact day of conception based on the weeks' gestation and the delivery date.

You can calculate this date more than 100 years in the past. Just enter the actual birthday of the baby and the weeks of pregnancy, and it will automatically calculate a range of dates when sex likely happened, when the baby was conceived, and the implantation date range. 

How is the conception date calculated?

Conception, the fertilization of the egg by the sperm usually happens 266 days before the due date and the due date is calculated 266 days after ovulation conception and fertilization. The last menstrual period usually happens about 14 days before ovulation, so the due date is calculated 280 days after the first day of the last menstrual period.

How does conception occur?

There are three primary steps in conception: ovulation, fertilization, and implantation. Ovulation is the first step, the ejection of a mature egg from the ovary. Fertilization occurs when the sperm penetrates the egg. Finally, implantation is when the fertilized egg attaches to the uterus.               


Every month, one of your ovaries has immature eggs that begin to develop in what are called follicles. Usually one of these follicles will begin to mature and the others will stop growing and eventually degenerate. Eventually, the follicle matures and releases the egg from the ovary, this is ovulation. Ovulation typically occurs approximately two weeks prior to your menstrual period. For about twenty-four hours after ovulation, the egg can be fertilized.

Finding out when and if you ovulate is one of the most important factors when trying to get pregnant. If you don't ovulate, you can't get pregnant.


For fertilization to occur sperm must be introduced to the egg and must then penetrate the egg. After the sperm enters the egg the coating around the egg is altered to keep other sperm from also penetrating the egg. It is at this moment that the genetic makeup of the baby is determined, including the sex. Because the mother is only able to provide an X chromosome the father must provide a Y chromosome if the baby is going to be a boy. If the father also provides an X chromosome the baby will be a girl.


Within twenty-four hours after the egg has been fertilized, it will begin dividing and will continue to do so as it makes its way through the fallopian tube and into the uterus. The fertilized egg will become a solid ball of cells and then a hollow ball of cells. At this point it will shed its protective coating and hormones will be released by your body to help it attach to your uterus. When the embryo attaches to your uterus you may have some slight bleeding. This is known as implantation bleeding.

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Pregnancy Symptoms: Early Signs You May Be Pregnant