Calculator

When is baby due?

The classic estimate uses Naegele's rule: 280 days from the first day of your last period, adjusted for your cycle length, or 266 days from conception if you know it. You will also see which week and trimester today falls in.

Count from

First day of my last periodConception date (if known)

First day of your last period

Usual cycle length28 days

If your cycles are not about 28 days, this shifts the estimate (a common convention). Irregular cycles make period dating less reliable, which the scan resolves.

Your estimate

Choose a date and press the button. Nothing you enter leaves this page.

Sources

Pregnancy due date calculator NHS, 2023
Methods for estimating the due date (Committee Opinion 700) American College of Obstetricians and Gynecologists, 2017First-trimester ultrasound is the most accurate dating method.

Last reviewed: 2026-07-16