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.
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.”
Calculation Formula for Naegele’s Rule
- Subtract 3 months from the LMP
- Add 7 Days to the LMP
- Add 1 Year
(use this calculation formula for patients whose LMP falls between April-Dec)
- Add 7 Days to LMP
- 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
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