How to Determine a Due Date From a Date of Conception

As much as we would like to know exactly when to expect a new baby's birthday, it is not that easy. It can take up to three days for an egg to become fertilized and to take hold of the uterine lining, so even if you have been keeping track of your basal temperature, you may be off by a few days. Also, 40 weeks is the average time most women are pregnant--it is not a hard and fast law of nature. So, keeping in mind that it is not possible to predict with 100 percent accuracy the exact day your baby will decide to appear, the steps below will help you get a reasonable estimate.

Instructions

• 1

  Add 280 days to the first day of your last period, if your cycle averages every 28 days, to find the due date.

• 2

  Add 40 weeks to the date you think you conceived, and that is your estimated due date.

• 3

  Add 266 days to the date you ovulated, if you have been keeping track of your basal temperature.

• 4

  Tell your health care provider the date of the first day of your last period, the average length of your cycle and your estimated date of conception. Allow her to do a pelvic exam and an HCG (Human Chorionic Gonadotropin, also known as "the pregnancy hormone") test, for a more accurate estimation of the gestational stage.