What is gestational age?

Gestational age is the age of a pregnancy measured in weeks and days from the first day of the last menstrual period (LMP). It is approximately two weeks longer than fetal age, which counts from conception. Healthcare providers universally use gestational age because the LMP date is more reliably known than the exact conception date.

Why use an ultrasound date instead of LMP?

An early ultrasound (before 14 weeks) can measure the embryo or fetus directly and is often more accurate than LMP dating, especially when cycles are irregular. If your ultrasound-derived gestational age differs from LMP dating by more than 5–7 days, your provider may adjust your official due date to match the ultrasound.

How is gestational age calculated from LMP?

The total days elapsed since the LMP date are divided by 7 to give complete weeks; the remainder is the extra days. For example, 73 days elapsed = 10 weeks and 3 days. The estimated due date (EDD) is LMP + 280 days (Naegele's rule).

How is gestational age calculated from an ultrasound?

Start with the gestational age recorded at the ultrasound date, then add the number of days that have passed since that scan. For example, if the scan showed 9 weeks 2 days on May 1, and today is May 15 (14 days later), current gestational age is 9 weeks 2 days + 14 days = 11 weeks 2 days.

What is the estimated due date (EDD)?

The EDD is the date at which the pregnancy reaches 40 weeks (280 days from LMP). Only about 5% of babies arrive on their exact due date; delivery between 37 and 42 weeks is considered normal. Always confirm your EDD with your healthcare provider.

Are these calculations a substitute for medical advice?

No. This tool provides estimates for informational purposes only. Gestational age and due date should always be confirmed by a qualified healthcare provider using clinical assessment and ultrasound.

Gestational Age Calculator

Name: Gestational Age Calculator
Availability: InStock
Author: Nham Vu

Enter your LMP date or a known gestational age from an ultrasound to instantly calculate your current gestational age in weeks and days, plus your estimated due date.

Gestational Age Calculator

First Day of Last Menstrual Period

Enter the first day of your most recent period.

How it works: Gestational age = days since LMP divided by 7. EDD = LMP + 280 days.

Fill in the form and click Calculate

Your gestational age will appear here

Summary

Enter your LMP date or a known gestational age from an ultrasound to instantly calculate your current gestational age in weeks and days, plus your estimated due date.

How it works

Method 1 computes elapsed days from LMP to today, converts to weeks plus remainder days, and adds 280 days for the EDD. Method 2 converts the ultrasound gestational age to a total day count, adds elapsed days since the scan, then converts back to weeks and days; the EDD is computed by subtracting the total gestational days from today and adding 280.

Use cases

Find out exactly how many weeks and days pregnant you are today.
Calculate your estimated due date from your LMP date.
Update gestational age forward from an ultrasound measurement.
Cross-check your provider's gestational age estimate.
Track pregnancy progress between prenatal visits.

Frequently Asked Questions

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Last updated: 2026-05-23 · Reviewed by Nham Vu