How Accurate Is a Due Date?

But data from the Perinatal Institute, a non-profit organisation, shows that an estimated date of delivery is rarely accurate - in fact, a baby is born on its predicted due date just 4% of the time.

How accurate is your due date by ultrasound?

As pregnancy progresses, the accuracy of an ultrasound for predicting due dates decreases. Between 18 and 28 weeks of gestation, the margin of error increases to plus or minus two weeks. After 28 weeks, the ultrasound may be off by three weeks or more in predicting a due date.

Are due dates usually early or late?

Twenty-six percent were born in weeks 37 to 38; 57 percent in weeks 39 to 40; 6 percent in week 41; and less than 1 percent at 42 weeks or beyond. In 2017, 73 percent of babies were born before their due dates. Two decades earlier, in 1997, that figure was 57 percent.