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Date & Time Tools

Due Date Calculator

Estimate a pregnancy due date from the last menstrual period, with gestational age and trimester.

Thursday, October 8, 2026

estimated due date

  • 23w 3dGestational age today
  • 2Trimester

An estimate using Naegele's rule (40 weeks). Only a clinician can confirm a due date.

How to use it

  1. Enter the LMP date The first day of the last menstrual period.
  2. Read the due date Estimated as 40 weeks from the LMP.
  3. Check the progress See the current gestational age and trimester.

Examples

LMP 1 Jan due 8 Oct
40 weeks 280 days

About this tool

The classic way to estimate a due date is Naegele’s rule: count 40 weeks from the first day of the last menstrual period. This calculator does that for you and also shows how far along a pregnancy is today, in weeks and days, along with the trimester.

It’s the same starting estimate clinicians use, but it assumes a regular cycle and can’t account for everything. Treat it as a guide, not a diagnosis — a healthcare professional can confirm the date, usually with an ultrasound. Everything runs in your browser.

Frequently asked questions

How is the due date estimated?

It uses Naegele's rule — 280 days (40 weeks) from the first day of the last menstrual period — the standard starting estimate.

Is this medically accurate?

It's a common estimate, but cycle length and other factors vary. Only a clinician, often with an ultrasound, can confirm a due date.

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Updated June 14, 2026