How Can I Calculate My Due Date?

How Can I Calculate My Due Date?

 It's a simple calculation:

Add seven days to the first day of your LMP, then subtract three months.

Using the example of June 1 as the first day of your last period, this would give a due date of March 8.

What if I Don't Know the Date of My Last Menstrual Period?

 If you have no idea when your last period was, your doctor may order an ultrasound to determine your due date.

An ultrasound allows your doctor to measure the crown-rump length (CRL), or length of the fetus from one end to the other. During the first trimester, this measurement provides the most accurate estimation for the age of the baby.



Ultrasound measurements for estimating the age of a fetus are more accurate during the early stages of pregnancy. In the first few weeks, fetuses tend to develop at the same rate.

 However, as pregnancy progresses, the rates of fetal growth begin to vary from pregnancy to pregnancy. This is why ultrasound measurements can’t be used to accurately predict the age of the baby in the later stages of pregnancy.