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Trying to conceive

Due date calculator: Find out when your baby will arrive

People say that pregnancy is a long nine months, but it's actually closer to 10! Find out when to expect your baby with a due date calculator.

By Today's Parent
Due date calculator: Find out when your baby will arrive

Photo: iStockphoto

Congrats on getting pregnant! Wondering when your baby will arrive? Use a due date calculator to find out.

How does a due date calculator work?

Everybody says that pregnancy is a long nine months, but it’s actually 40 weeks—which is more like 10 months! In general, it takes about 280 days to grow and gestate a baby, but it’s hard to know the exact day of conception (sperm can hang around in the reproductive system for a few days after you have sex). Plus, 40 weeks is only an average: Some babies wait 42 weeks before they make their big debut. Fun fact: The week of your last period and the week you ovulated are included in the 40 weeks, so if you go into labour on your due date, your baby is actually only 38 weeks old.

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Due date calculator: Find out when your baby will arrive

How do doctors calculate a due date?

Many doctors use a method that sounds like a math test problem: Take the first day of your last menstrual period, add seven days and subtract three months. (For example, if you got your last period on March 1, you would add seven days to get March 8, then backtrack three months. February 8, January 8, December 8—this is your due date!)

Calculating a due date with an ultrasound

Even if you think you know the exact night you conceived, some doctors prefer to date ultrasounds, which help them measure the gestational age of a fetus. Early in the first trimester, the technician may use a transvaginal wand if the uterus is deep in the pelvis or if the woman is overweight to get an image of the teeny-weeny baby (it looks more like a little blob or bean at this stage). Typically, the ultrasound is done over the stomach.

Follow along as your baby grows with Pregnancy by Week.

This article was originally published on Jun 19, 2013

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