What is Naegele's rule?

A clinical estimate: due date = first day of last menstrual period (LMP) + 280 days (40 weeks). Assumes a regular 28-day cycle with ovulation on day 14.

How accurate is this?

Only about 4-5% of babies are born on their estimated due date. Most deliveries fall within ±2 weeks. Ultrasound dating in the first trimester is more accurate.

Is this medical advice?

No. This tool is for informational purposes only. Always consult your physician, midwife, or OB-GYN for pregnancy care decisions.

Pregnancy Due Date Calculator

Date & Time· 10 tools

Free pregnancy due date calculator. Enter the first day of your last menstrual period (LMP) to estimate your due date using Naegele's rule — widely used by clinicians to estimate the expected delivery date.

First day of last menstrual period (LMP)

Estimated due date

Friday, February 19, 2027

280 days to go

Gestational age

0w 0d

Trimester

Est. conception

Friday, May 29, 2026

Informational estimate only. Not medical advice. Consult your physician, midwife, or OB-GYN for pregnancy care decisions.

Frequently Asked Questions

References

Prenatal Care — ACOG FAQ — American College of Obstetricians and Gynecologists
Pregnancy — health topic — World Health Organization

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Frequently Asked Questions

References and sources

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