Patient education: Pregnancy due date calculator (Beyond the Basics)
- Vanessa A Barss, MD, FACOG
Vanessa A Barss, MD, FACOG
- Senior Deputy Editor — UpToDate
- Deputy Editor — Obstetrics, Gynecology and Women's Health
- Associate Clinical Professor of Obstetrics, Gynecology and Reproductive Biology
- Harvard Medical School
WHAT IS MY DUE DATE?
Your due date, also called the estimated date of delivery, is 280 days from the first day of your last menstrual period (LMP). Most women deliver in the two weeks before or after their due date. About 4 percent of pregnant women deliver on their due date.
Due date calculator — If you have regular monthly menstrual cycles and know the first day of your last menstrual period, you can determine when your baby is due (estimated due date) and how far along you are in your pregnancy now (estimated gestational age) by using the following calculator (calculator 1).
Ultrasound — If you do not have regular monthly menstrual cycles or do not know when your last menstrual period started, you will need to have an ultrasound examination to determine your due date. This examination should be done as soon as possible because ultrasounds done after the fourth to fifth month of pregnancy are not very reliable for predicting due dates.
WHY IS THE DUE DATE IMPORTANT?
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