Due Date Calculator

Calculate the estimated due date from the first day of the last period.

Your dates

First day of your last period

Average cycle length (days)

Your due date

Enter the first day of your last period and press Calculate to estimate your due date.

Estimates use Naegele's rule: 40 weeks (280 days) from the first day of your last period, adjusted for your cycle length. Due dates are estimates, not guarantees - every pregnancy is different. Always confirm with your care provider.

Tool Introduction

This calculator estimates your due date using Naegele's rule, the standard formula used worldwide: 40 weeks from the first day of your last menstrual period, plus one day for each day your cycle is longer than 28 (or minus one for each day shorter).

Alongside the due date you get your current week of pregnancy, the trimester you are in, overall progress and a timeline of key dates across the three trimesters.

All calculations happen locally in your browser - nothing you enter is stored or sent anywhere.