Naegel’s rule in pregnancy

rule in pregnancy

 Naegele’s Rule is commonly used to calculate a woman’s estimate delivery date (EDD). When pregnancy take place you will be required to know how to calculate a woman’s due date by using Naegele’s Rule. 

Naegele’s Rule

Main points about Naegele’s Rule:

  • Commonly used to estimate an expected due date based on the woman’s last menstrual period (LMP).
  • Always assumes that the woman has a 28 day menstrual cycle (very rare) and that it will be a gestation time frame of 280 days (40 weeks)… again this varies because gestation is slightly longer for first baby birth.
  • February has 28 days (regardless of a leap year…to keep things simple).
  • Keep in mind the months have 30 days vs 31 days (September, April, June & November have 30 days)

“Thirty days has September,April, June, and November.

All the rest have thirty-one except for February alone,

Which has but twenty-eight days clear,

And twenty-nine in each leap year.”

naegele rule

Calculation Formula for Naegele’s Rule

LMP Date

  1. Subtract 3 months from the LMP
  2. Add 7 Days to the LMP
  3. Add 1 Year

(use this calculation formula for patients whose LMP falls between April-Dec)


LMP Date

  1. Add 7 Days to LMP
  2. Then add 9 months

(use this calculation formula for patients whose LMP falls between January-March rather than the other formula)

*Please understand how above for why it is best to use these different calculations based on when the LMP falls to prevent errors.

Naegele’s Rule Example:

Example 1: LMP: February 5, 2018

+ 7 days

February 12, 2018

+9 months=

EDD:  November 12, 2018

Example 2: LMP: September 28, 2018

– 3 months

June 28, 2018

+ 7 days

July 5, 2018

+ 1 year=

EDD:  July 5, 2019

EDD means Estimated delivery date

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