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Due Date Calculator

 Your expected delivery date (EDD) is 40 weeks from the first day of your last menstrual period (LMP). If you deliver on your EDD, your baby is actually only 38 weeks old - that's because your menstrual period and ovulation are counted as the first 2 weeks of pregnancy.  It's important to remember that your due date is only an estimate - most babies are born between 38 and 42 weeks and only a small percentage of women actually deliver on their due date.

Due Date/Conception Calculator 

(Days of the week are optional. The calculator will automatically determine them.)
Date of your last menstrual period:
  
 
 
Conception Occurred:
(about two weeks after last menstrual period)
First Trimester Ends (12 weeks) :
Second Trimester Ends (27 weeks) :
Estimated Due Date (40 weeks) :
On , you will be weeks pregnant.
   

A little history on this subject, shall we?

Dr. Naegele, circa 1850, determined that the average length of human gestation was approximately 266 days from conception. He assumed that the average woman had cycles that lasted 28 days and that she ovulated on Day 14 of her cycle (riiiiiiiiiiight!).

He used his data to come up with a mathematical calculation for due dates:

((LMP + 7 days) - 3 months) = Due Date
EX: ((January 1, 1996 + 7 days) - 3 months) = October 8, 1996

However, Dr. Naegele did not consider certain factors in his calculation. For example: Not every woman ovulates on Day 14 (o really??).

One study indicates that we need to add 15 days to the Naegele EDC for Caucasian, first time moms, and 10 days for Caucasian moms having subsequent children. African American and Asian women tend to have shorter gestations.

Nowadays, we use ultrasound, when available or if there is a question of menstrual history. Ultrasound can be an effective way of dating a pregnancy, but this accuracy is lost if not performed in the first half of pregnancy.

Most folks agree that there are many ways to date a pregnancy, and that not just one factor should be used to determine the final due date. Other factors to consider are: