EDC 11/8/01 LMP February 1, 2001 - add 7 days=February 8 subract 3 months=November 8, 2000 + one year =November 8, 2001.

The calculated estimated date of confinement (EDC) is determined by Naegele's Rule.

Naegle's Rule: Add 7 days to the first day of the last menstrual period (LMP) count back 3 months and add one year.
This is based on the assumption that a normal gestation is 280 days and that the patient has a 28-day menstrual cycle. Statistically, the majority of pregnancies deliver within 2 weeks before or after the calculated EDC.

In calculating estimated date of confinement when the patient's cycle is irregular, an ultrasound measurement may be needed. This may be done between the 14th and 20th week of gestation.

First Example: LMP 4/20/01 Therefore, add 7 days - 4/27/01
Count back 3 months - 1/27/01 Add one year - 1/27/02
EDC = 1/27/02

Second Example: LMP 6/4/01 Add 7 days - 6/10/01
Count back 3 months - 3/10/01 Add one year - 3/10/02
EDC = 3/10/02

21 year old female with regular menses - LMP 8/15/01
What is the EDC? (5/22/02)

32 year old female with regular menses - LMP 10/22/01
What is the EDC? (7/29/02)