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Pregnancy Due Date Calculator

Calculate your due date from LMP or conception date. Shows trimester timeline, gestational age, and week-by-week milestones.

Calculate Your Due Date

Select a calculation method and enter the relevant date.

First Day of Last Menstrual Period

The first day of your most recent period, used for Naegele's rule (LMP + 280 days).

How Is a Pregnancy Due Date Calculated?

A pregnancy due date, also called the estimated date of delivery (EDD), is the approximate date when a baby is expected to be born. While only about 5% of babies arrive exactly on their due date, the estimate is a critical reference point for prenatal care, scheduling tests, and monitoring fetal development throughout the pregnancy.

Naegele's Rule

The most widely used method for calculating a due date is Naegele's rule, developed by German obstetrician Franz Naegele in the early 19th century. The formula is straightforward: take the first day of the last menstrual period (LMP), add 280 days (40 weeks), and the result is the estimated due date. This assumes a 28-day menstrual cycle with ovulation occurring around day 14. For women with shorter or longer cycles, the estimate may be adjusted by a healthcare provider.

When the conception date is known instead, the calculation uses 266 days (38 weeks) from the date of conception, since conception typically occurs about two weeks after the start of the last period.

Understanding Gestational Age

Gestational age is measured from the first day of the last menstrual period, not from the date of conception. This means that during the first two weeks of "pregnancy," conception has not yet occurred. Gestational age is expressed in weeks and days (for example, 28 weeks and 3 days) and is the standard way that healthcare providers track pregnancy progress.

Trimester Milestones

A pregnancy is divided into three trimesters, each with distinct developmental milestones:

First Trimester (Weeks 1–12): All major organs and body systems begin to form. By the end of this trimester, the risk of miscarriage drops substantially. Early prenatal visits, blood work, and the first ultrasound typically occur during this period.
Second Trimester (Weeks 13–27): Often called the most comfortable trimester, this period includes the anatomy scan around week 20, where detailed images of the baby's organs are reviewed. The baby begins to move noticeably, and the viability milestone is reached around week 24, meaning the baby could potentially survive outside the womb with intensive medical support.
Third Trimester (Weeks 28–40): The baby gains weight rapidly and the lungs mature. At 37 weeks the pregnancy is considered early term. Regular monitoring increases in frequency, and preparations for delivery begin.

Key Pregnancy Milestones

12 Weeks: End of the first trimester. Major organs are formed, and the risk of pregnancy loss decreases significantly.
20 Weeks: The mid-pregnancy anatomy scan provides a detailed look at the baby's development and can often reveal the sex of the baby.
24 Weeks: The threshold of viability. Babies born at this stage have a chance of survival with advanced neonatal intensive care.
37 Weeks: The pregnancy is classified as early term. Babies born at this point generally do well without intensive medical intervention.
40 Weeks: The standard estimated due date. Pregnancies that continue past 41 or 42 weeks are considered post-term and may require induction.

Factors That Affect Due Date Accuracy

Due date calculations based on the LMP assume a regular 28-day cycle. Irregular cycles, uncertain period dates, or assisted reproduction can affect accuracy. First-trimester ultrasound measurements, particularly crown-rump length, are often used to confirm or adjust the due date and are generally considered more accurate than LMP-based calculations alone.

Disclaimer

This calculator is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Every pregnancy is unique, and only a qualified healthcare provider can give you an accurate due date based on your individual medical history, physical examination, and ultrasound findings. Always consult your doctor, midwife, or obstetrician for personalized prenatal care and guidance.

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How to Use the Pregnancy Due Date Calculator

1
Enter your values
Open the Pregnancy Due Date Calculator and fill in the required input fields with your numbers or selections.
2
Review the calculation
The tool automatically computes the result as you type. Double-check your inputs to ensure accuracy.
3
Interpret your results
Review the calculated output along with any breakdowns, charts, or explanations provided to understand what the numbers mean for your situation.

Sources & Verification

Formulas based on peer-reviewed research cited by CDC and NIH

Centers for Disease Control and Prevention National Institutes of Health World Health Organization

Published by ConvertCrunch Editorial Team | Our Methodology

Frequently Asked Questions

What is the Pregnancy Due Date Calculator?

The Pregnancy Due Date Calculator is a free browser-based tool on ConvertCrunch. Calculate your due date from LMP or conception date. Shows trimester timeline, gestational age, and week-by-week milestones. It requires no downloads, installations, or account signups. Simply enter your values and get instant, accurate results. The tool is designed for quick calculations and informed decision-making, whether you are a professional, student, or everyday user looking for reliable answers.

How do I use the Pregnancy Due Date Calculator?

Using the Pregnancy Due Date Calculator is straightforward. Enter your values into the input fields provided on the page, then calculate or adjust parameters to explore scenarios. Most processing happens locally in your browser. If a feature uses a third-party service, the tool identifies that connection and the privacy policy explains it. Most users get the answers they need in under a minute.

Is the Pregnancy Due Date Calculator free to use?

Yes, the Pregnancy Due Date Calculator is completely free to use with no account signup, email requirement, or premium tier. Most calculations run locally in your browser. Features that depend on live data or a third-party service require a network connection and are identified in the tool. You can use it as many times as you need for personal, educational, or professional purposes.

How accurate is the Pregnancy Due Date Calculator?

The Pregnancy Due Date Calculator uses peer-reviewed scientific formulas that are widely accepted in clinical and fitness settings. Results are estimates based on population averages and may not perfectly reflect your individual physiology due to factors like genetics, body composition, and medical conditions. This tool is for informational purposes only and is not a substitute for professional medical advice. Consult a healthcare provider for personalized guidance.

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