How is the due date calculated from the last menstrual period (LMP)?

The most common method, known as Naegele's rule, is used to calculate your estimated due date (EDD). The formula works by adding 280 days (or 40 weeks) to the first day of your last menstrual period. This calculation assumes you have a regular 28-day menstrual cycle, with ovulation typically occurring on day 14.

How accurate is this due date calculator?

This calculator provides a reliable estimate based on the information you provide. However, it's important to remember that it's a tool for estimation purposes only. In reality, only about 5% of babies are born on their exact due date. Your doctor or midwife will give you the most accurate due date, which is often confirmed or adjusted based on an early ultrasound measurement of the baby.

What are the three trimesters of pregnancy?

Pregnancy is divided into three trimesters, each marking different phases of fetal development. The First Trimester runs from week 1 to the end of week 13. The Second Trimester is from week 14 to the end of week 27. The Third Trimester starts at week 28 and continues until you give birth.

What is the difference between gestational age and fetal age?

Gestational age is counted from the first day of your last menstrual period (LMP). This is the standard measurement doctors use, and it means pregnancy is measured as 40 weeks long. Fetal age is the actual age of the growing baby, counted from the date of conception. Fetal age is typically two weeks behind the gestational age.

Pregnancy Due Date Calculator

Q: Can my due date change?

Yes, it's possible for your due date to change, especially after your first ultrasound scan. An early ultrasound (typically between 8 and 14 weeks) is the most accurate method for dating a pregnancy. If the ultrasound date differs significantly from the date calculated by your LMP, your doctor may decide to adjust your official due date.

Find your estimated due date and explore your pregnancy timeline week by week.

Calculate from:

First Day of Last Period

Understanding Your Pregnancy Journey

Congratulations! Finding out your estimated due date is one of the first and most exciting steps in your pregnancy journey. This due date calculator is designed to be your companion, providing an accurate estimate of your baby's arrival and offering a glimpse into the incredible development happening week by week. Knowing your timeline helps you prepare for the important milestones ahead, from your first prenatal visit to the big day.

How to Use This Due Date Calculator

We provide three different ways to calculate your estimated due date (EDD) for maximum accuracy:

Last Menstrual Period (LMP): This is the most common method. Simply enter the first day of your last period. The calculator adds 40 weeks (280 days) to this date to estimate your due date.
Conception Date: If you tracked ovulation and know the exact date of conception, this method is highly accurate. Your due date is calculated by adding 38 weeks (266 days) to this date.
Ultrasound Data: An early pregnancy ultrasound is the most precise way to determine gestational age. Enter the date of your ultrasound and the weeks and days the scan measured to get a refined due date.

Navigating the Three Trimesters of Pregnancy

Your pregnancy is divided into three distinct stages, or trimesters. Each one brings new developments for both you and your baby.

First Trimester (Weeks 1-13): This is a period of rapid, foundational growth. The fertilized egg implants, and all the baby's major organs and body systems begin to form. You'll hear the first heartbeat, and by the end of this trimester, your tiny baby is fully formed.
Second Trimester (Weeks 14-27): Often called the "golden trimester," many early pregnancy discomforts like morning sickness tend to fade. Your baby grows quickly, and you'll likely feel their first movements (quickening). This is often when parents find out the baby's sex.
Third Trimester (Weeks 28-40+): This is the final stretch! The baby focuses on gaining weight and maturing, especially their lungs and brain. They will settle into a head-down position to prepare for birth. You'll be busy with final preparations as you await your new arrival.

Frequently Asked Questions (FAQ)

Here are answers to some common questions about due dates and pregnancy timelines.

How accurate is a due date from the last period?

Calculating from your LMP is quite accurate, especially if your menstrual cycle is regular (around 28 days). It's the standard method used by doctors to set an initial due date. However, its accuracy decreases for those with irregular cycles.

Can my due date change?

Yes, and it's very common for a due date to be adjusted. Your doctor will likely perform an ultrasound in the first trimester. If the baby's measurements suggest a different gestational age than your LMP date, your doctor may update your official due date.

What is the difference between gestational and fetal age?

Gestational age is counted from the first day of your last period, which is about two weeks before conception. This is the 40-week timeline doctors use. Fetal age is the baby's actual age since conception. So, if you are 8 weeks pregnant (gestational age), your baby's fetal age is about 6 weeks.

Medical Disclaimer: This tool provides an estimate for informational purposes and is not a substitute for professional medical advice. Always consult with your healthcare provider for the most accurate information regarding your pregnancy. Your doctor will monitor your progress and provide the most reliable due date.