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Pregnancy Due Date Calculator

Estimate your due date

Enter the first day of your last period or your conception date to estimate your due date and current pregnancy week.

First day of last period

About the pregnancy due date calculator

A pregnancy due date is an estimate, not a guarantee — only about 5% of babies arrive on the exact date. Still, it gives you and your care team a useful timeline for tracking milestones, scheduling appointments, and preparing for birth.

This calculator uses Naegele’s rule: counting forward 280 days (40 weeks) from the first day of your last menstrual period (LMP). If you know your conception date, it counts forward 266 days instead. The result also shows how many weeks and days pregnant you are today and which trimester you are in.

The rule

  • From LMP: due date = LMP + 280 days
  • From conception: due date = conception + 266 days

How to use the pregnancy due date calculator

  1. Choose a method

    Use your last period (LMP) or conception date.

  2. Enter the date

    Pick the first day of your last period or your conception date.

  3. See your timeline

    Your estimated due date, current week and trimester appear instantly.

Frequently asked questions

How accurate is the due date?
It is an estimate based on averages. Most babies arrive within two weeks of the due date. Early ultrasound scans can provide a more accurate date, especially in the first trimester.
What if my cycle is longer or shorter than 28 days?
Naegele’s rule assumes a 28-day cycle. For shorter or longer cycles, adjust mentally (a longer cycle pushes the due date later). Your care provider can refine the estimate.
What is a full-term pregnancy?
A full-term pregnancy lasts about 40 weeks, counted from the first day of the LMP. Births between 37 and 42 weeks are considered term.
Is this calculator free?
Yes — free, no sign-up, and all calculation runs in your browser.

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