How is my due date calculated?

The most common method is Naegele's Rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP). Your healthcare provider may adjust based on ultrasound measurements.

How accurate is a due date calculator?

Only about 5% of babies are born on their due date. Most are born within 2 weeks before or after. First-trimester ultrasound is the most accurate method for dating a pregnancy.

A due date calculator estimates your baby's expected arrival date based on your last menstrual period (LMP) or conception date, using the standard 280-day (40-week) pregnancy calculation.

Due Date Calculator

Estimate your baby's due date based on your last period, conception date, IVF transfer, or ultrasound measurements.

Calculation Method

First Day of Last Menstrual Period

Only about 5% of babies are born on their due date. Most are born within 2 weeks before or after. Your healthcare provider may adjust your due date based on ultrasound measurements.

Sources

ACOG — Methods for Estimating Due Date
March of Dimes — Due Date Calculator