Every Single Way to Estimate Your Due Date

When is my due date?

Due Date on the Calendar
Photo © Jamie Grill/Getty Images

How Are Due Dates Calculated?

Your due date is typically calculated based on the first day of your last menstrual period (LMP). Pregnancy is 266 days from conception, or about 280 from your LMP. This is 40 weeks or 9 months (give or take a few weeks). You can calculate your own due date or wait for your first appointment with your doctor or midwife. Just remember, it's an estimate, no matter how you slice it.

Write it on your calendar in pencil.

What If I Don't Know When My Last Period Was?

Sometimes a woman will come in for prenatal care and will not know when her last period was or when she got pregnant. If this is the case, then your doctor or midwife will use an early ultrasound, the earlier the more accurate, to help you determine your due date. There are also other methods if you are out of your first trimester.

Can Due Dates Be Wrong?

Sometimes a due date is given to you based on your last period, but it turns out to be wrong because of some fluke, like implantation bleeding, longer cycles, illness, etc.. Having an accurate due date is important because it can help prevent misleading prenatal test results and other risks including prematurity because of a mistimed due date and induction.

Watching Baby Based on Due Date

Being able to follow your baby's growth through pregnancy is one of the best parts of pregnancy. If you like to watch your baby grow based on how far along you are in gestation, here are some great places to start:

Your due date is not set in stone.

Some practitioners have said that rather than give women specific days that we think their babies will be born, we should give them monthly time frames, like "You're due near the end of February or the month of May." This is to keep the stress levels from rising as the due date draws near, and even more oddly - passes. Marking a calendar doesn't mean your baby can read it! Read more.

What If My Due Date Passes?

The first thing to do is to realize that it was a guess to begin with, most babies are born within two weeks of their due date, in either direction. If your pregnancy finishes 42 weeks, then the American Congress of Obstetricians and Gynecologists (ACOG) says that an induction of labor should be considered, but not before the completion of the 42 week mark, except for medical indications. Some practitioners may discuss options for induction after the 41st week of pregnancy depending on your medical history and preferences. 


Gülmezoglu AM, Crowther CA, Middleton P, Heatley E. Induction of labour for improving birth outcomes for women at or beyond term. Cochrane Database of Systematic Reviews 2012, Issue 6. Art. No.: CD004945. DOI: 10.1002/14651858.CD004945.pub3

Whitworth M, Bricker L, Mullan C. Ultrasound for fetal assessment in early pregnancy. Cochrane Database of Systematic Reviews 2015, Issue 7. Art. No.: CD007058. DOI: 10.1002/14651858.CD007058.pub3