Knowing your due date during pregnancy is important from many points of view. Firstly, it helps to monitor fetal development, correlating ultrasonographic findings with the actual gestational period. Many a times, a disparity in these findings could indicate a problem such as intrauterine growth retardation. A full term pregnancy can last from 38 to 42 weeks. Delivery before this period leads to premature birth and carries various health risks to the fetus, and if there are no labor pains up to 42 weeks, an induction of labor or a caesarian section delivery becomes necessary.

Naegele’s rule is a simple way of calculating the pregnancy due date. Adding 9 calendar months and 7 days to the first day of the last menstrual period gives the approximate due date for delivery.