Close-up, high-key photo of a newborn baby getting examined by a doctor.
Pregnant? Odds are, your baby is coming early.

“When are you due?”

It’s a question you hear all the time when you’re pregnant, and it’s usually a pretty easy one to answer. Early on in a pregnancy, your doctor will calculate a “due date” based on the standard gestation term—about 280 days, or 40 weeks.

But odds are that date is wrong.

Advertisement - Continue Reading Below

Most women will give birth seven days before their due date, according to an analysis of birth information put together for The Boston Globe by Brookings Institute researcher and WhenToExpect.com co-creator Matt Chingos.

You can do a little more due date predicting based on the number of children you’ve already had. The study shows that first children tend to arrive two to three days before their due date, while second and third children are usually five to six days early.

The age of the mother is another key factor. Moms in their 40s are more likely to deliver a week early, whereas teen moms stick closer to their projected due date. It all correlates with the previous point about birth order: Teen moms are usually giving birth to their first child.

Only 5 percent of the women delivered before 39 weeks.

Could you guess anything about your due date based on whether you’re having a girl or a boy? Sorry, you’re out of luck. Boys and girls arrive at about the same time.