Enter the first day of the last menstrual period into the calculator to determine the expected date of delivery.

## Naegele’s Rule Formula

The following formula is used to calculate the expected date of delivery using Naegele’s Rule.

EDD = LMP + 1 year - 3 months + 7 days

Variables:

- EDD is the expected date of delivery
- LMP is the first day of the last menstrual period

To calculate the expected date of delivery, add one year to the first day of the last menstrual period, then subtract three months. Finally, add seven days to the result. This method assumes a 28-day menstrual cycle with ovulation occurring on the 14th day, and a standard gestation period of 280 days from the last menstrual period to the birth of the baby.

## What is a Naegele’s Rule?

Naegele’s Rule is a standard method used by obstetricians to estimate a pregnant woman’s due date. The rule calculates the expected date of delivery by adding one year, subtracting three months, and adding seven days to the first day of a woman’s last menstrual period. This method assumes a 28-day menstrual cycle with ovulation occurring on the 14th day, and a standard gestation period of 280 days from the last menstrual period to the birth of the baby.

## How to Calculate Naegele’s Rule?

The following steps outline how to use Naegele’s Rule to calculate the expected date of delivery (EDD).

- First, determine the first day of the last menstrual period (LMP).
- Next, add 1 year to the LMP.
- Then, subtract 3 months from the previous step.
- Finally, add 7 days to the result to calculate the EDD.

**Example Problem:**

Use the following variables as an example problem to test your knowledge.

LMP: January 15, 2022

EDD = LMP + 1 year – 3 months + 7 days