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Pregnancy Due Date Calculator

Calculate your estimated due date from your last period or conception date. See current week, trimester, and pregnancy progress.

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Pregnancy Details

Estimated Due Date

Sunday, December 27, 2026

Week 8, Day 020.0%
Week 1Week 13Week 28Week 40

Trimester

First

Current Week

Week 8

Days Left

224
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How to Use Pregnancy Due Date Calculator

  1. 1

    Choose method

    Select whether to calculate from your last menstrual period (LMP) or conception date.

  2. 2

    Enter date

    Enter the first day of your last period or your estimated conception date.

  3. 3

    View due date

    See your estimated due date, current week, and trimester.

  4. 4

    Track progress

    View a progress bar showing where you are in your pregnancy.

Frequently Asked Questions

Using Naegele's rule: from LMP, add 280 days (40 weeks). From conception, add 266 days (38 weeks). Only about 5% of babies are born on their exact due date; most arrive within 2 weeks before or after.

First trimester: Weeks 1-12 (organ development). Second trimester: Weeks 13-27 (growth and movement). Third trimester: Weeks 28-40 (rapid growth, preparation for birth).

This provides an estimate based on average pregnancy duration. Ultrasound dating in the first trimester is more accurate. Your healthcare provider may adjust your due date based on ultrasound measurements.

If you know your conception date, use that option instead. Otherwise, an early ultrasound (before 12 weeks) can accurately estimate gestational age and due date.

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How Due Date Calculations Work

Naegele's rule — the standard method used since 1812 — adds 280 days (40 weeks) to the first day of the last menstrual period (LMP). This assumes a 28-day cycle with ovulation on day 14, meaning actual gestation is approximately 266 days from conception. If your cycles are longer or shorter than 28 days, the estimate shifts accordingly: a 35-day cycle means ovulation likely occurred around day 21, pushing the due date about a week later.

How Accurate Are Due Dates?

Only about 4-5% of babies are born on their exact estimated due date. The majority (about 80%) arrive within the window of 37-41 weeks. First-time mothers tend to deliver slightly later on average. First-trimester ultrasound dating (measuring crown-rump length between 8-13 weeks) is more accurate than LMP-based dating, with a margin of error of about 5-7 days versus 2-3 weeks for LMP alone.

Understanding Trimesters

The first trimester (weeks 1-12) is when all major organs form — this is the highest-risk period for miscarriage and when morning sickness peaks. The second trimester (weeks 13-27) is often called the "golden period" as energy returns and the baby grows rapidly. The third trimester (weeks 28-40) involves rapid weight gain, lung maturation, and preparation for delivery. Each trimester has different nutritional needs, exercise considerations, and medical screening milestones.