Due Date Calculator

Estimated delivery date by Naegele's rule

Calculate your estimated due date (EDD) from the first day of your last menstrual period using Naegele's rule, the standard method accepted by ACOG.

For guidance only. The calculated date is an estimate. Only your doctor or midwife can confirm gestational age with an ultrasound.

First day of your last menstrual period (LMP)

Enter the date of the first day of your last period

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How it works

1Identify the first day of your last menstrual period (LMP).
2Naegele's rule adds 280 days (40 weeks) to the LMP.
3Get the estimated due date, current gestational age, and trimester.
4Share the result with your doctor or midwife for follow-up.

Frequently asked questions

Due date calculator: pregnancy weeks and estimated delivery date

The estimated due date (EDD) predicts when the baby will be born. It is calculated using Naegele's rule: add 280 days (40 weeks) to the first day of the last menstrual period (LMP). Only 5% of babies are born exactly on the calculated date.

Naegele's rule

Developed by obstetrician Franz Karl Naegele in 1812: EDD = LMP + 9 months + 7 days (or equivalently, LMP + 1 year − 3 months + 7 days). Assumes a 28-day menstrual cycle with ovulation on day 14.

Pregnancy trimesters

First trimester: weeks 1-12. Formation of vital organs.
Second trimester: weeks 13-27. Accelerated development, baby movements.
Third trimester: weeks 28-40. Growth and lung maturation.
Full term: weeks 37-42. Most deliveries occur in this range.

Ultrasound date vs. LMP date

The first-trimester ultrasound (weeks 8-13) is the most accurate method for dating the pregnancy. If there is a difference of more than 5-7 days from the LMP-calculated date, doctors adjust the EDD to the ultrasound date.

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