Estimating Your Due Date

If you know when your baby was conceived, you may have already estimated your baby's due date. At your first prenatal exam, your health care provider will ask you questions to try to predict your due date as precisely as possible.

Knowing your baby's due date can help in many ways. It helps to monitor your baby's growth more accurately. Because certain laboratory tests change throughout your pregnancy, knowing an accurate due date will also allow your provider to track these tests better. It also helps your doctor to manage preterm labor if it occurs.

How Is My Due Date Determined?

Normally, your due date is 280 days (40 weeks or about 10 months -- yes, 10 months,also known as 10 lunar months!) from the first day of your last period. However, if your periods are not regular or are not 28 days in cycle, your due date may be different from the "280-day rule." Your health care provider may order an ultrasound to more accurately determine your due date.

If you are certain of your conception date (the date when you got pregnant), please tell your health care provider. This information can be helpful in determining your estimated date of delivery (EDD).

A full-term pregnancy lasts from 37 to 42 weeks, so your actual date of delivery can be different from your estimated date of delivery, which is sometimes called estimated date of confinement, or EDC. A very small number of babies are actually born on their due dates.

Reviewed by The Cleveland Clinic Birthing Services and the Department of Obstetrics and Gynecology.