What Percentage of Babies Are Born On Their Due Date?

by | Jun 18, 2021

I’m going to cost my parents a lot of money

The estimated due date that obstetricians provide assume that pregnancy lasts 40 weeks. But there is no timer that goes off at 40 weeks that signals that labor should occur — it is considered normal to give birth up to two weeks before or after the due date. Determining the day that the pregnancy began is also imprecise and makes predicting a due date that much more challenging.

A study of 18,708 births in Australia found that a mere 5% of babies were born on their estimated due date, and only 66% occurred within seven days. Here’s a histogram from the study showing the number of days between the date of birth and the due date.


Similarly, here’s a chart showing the length of pregnancies in the U.S. over a three year period:



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