Official reprint from UpToDate®
www.uptodate.com ©2017 UpToDate®

Patient education: Pregnancy due date calculator (Beyond the Basics)

Vanessa A Barss, MD, FACOG
Section Editor
Louis Leff, MD, FACP
Deputy Editor
Kristen Eckler, MD, FACOG
0 Find synonyms

Find synonyms Find exact match



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.


Health care providers use the due date to figure out how far along you are in your pregnancy when you see them, both before and after your due date. A lot of decisions are based upon this information. For instance, deciding when to do certain lab tests or other tests on you or your baby and whether labor is starting too early or too late.

Literature review current through: Mar 2017. | This topic last updated: Wed Aug 12 00:00:00 GMT 2015.
The content on the UpToDate website is not intended nor recommended as a substitute for medical advice, diagnosis, or treatment. Always seek the advice of your own physician or other qualified health care professional regarding any medical questions or conditions. The use of this website is governed by the UpToDate Terms of Use ©2017 UpToDate, Inc.

All topics are updated as new information becomes available. Our peer review process typically takes one to six weeks depending on the issue.