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Your Pregnancy Due Date Calculator

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Updated June 02, 2014

Pregnancy Wheel - Gestation Calculator

Many doctors and midwives use a pregnancy wheel to quickly calculate a due date.

Photo © Ankevanwyk | Dreamstime.com

How are due dates calculated?:

Your due date is typically calculated based on the first day of your last menstrual period (LMP). Pregnancy is 266 days from conception, or about 280 from your LMP. This is 40 weeks or 9 months (give or take a few weeks).

What if you don't know when your last period was?:

Then your doctor or midwife will use an early ultrasound, the earlier the more accurate, to help you determine your due date.

When due dates are wrong?:

Sometimes a due date is given to you based on your last period, but it turns out to be wrong because of some fluke, like implantation bleeding. Having an accurate due date is important because it can help prevent misleading prenatal test results including prematurity.

Watching Your Baby Based on Due Date:

If you like to watch your baby grow based on how far along you are in gestation, here are some great places to start:

What your due date is not...:

Your due date is not set in stone. Some practitioners have said that rather than give women specific days that we think their babies will be born, we should give them monthly time frames, like "You're due near the end of February or the month of May." This is to keep the stress levels from rising as the due date draws near, and even more oddly - passes. Marking a calendar doesn't mean your baby can read it!

What if your due date passes?:

The first thing to do is to realize that it was a guess to begin with, most babies are born within two weeks of their due date, in either direction. If your pregnancy finishes 42 weeks, then the American College of Obstetricians and Gynecologists (ACOG) says that an induction of labor should be considered, but not before the completion of the 42 week mark, except for medical indications.
  1. About.com
  2. Health
  3. Pregnancy & Childbirth
  4. Prenatal Care
  5. Due Dates
  6. Over Due Pregnancy
  7. Calculating Your Due Date - When Is My Baby Due?

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