How accurate is a due date calculated from LMP?

Within 2-4 days for most women with regular cycles. An early ultrasound (before 14 weeks) provides the most accurate dating. Your healthcare provider may adjust the due date based on ultrasound measurements.

What if my periods are irregular?

LMP-based calculations are less accurate with irregular cycles. An early ultrasound measuring the fetal crown-rump length (CRL) is the most accurate way to establish your due date.

What is gestational age vs fetal age?

Gestational age is counted from the LMP and is what doctors use. Fetal age (conception age) is approximately 2 weeks less. Our calculator displays gestational age, as used medically.

What week is a baby considered full-term?

Full-term is 39-40 weeks. 'Early term' is 37-38 weeks, 'late term' is 41 weeks, and 'post-term' is 42+ weeks. The goal is to reach 39 weeks before delivery for the best outcomes.

Can I get an accurate due date from a home pregnancy test?

No, home tests only confirm pregnancy. Due date calculation requires knowing your LMP or using an ultrasound. The test does not indicate how far along you are.

[Бесплатно] Pregnancy Due Date Calculator (Free) — Calculate Your Baby's Arrival Date

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Calculation Details

Method

First Day of Last Period

Due Date Result

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Only 5% of babies are born on their exact due date. This tool provides an estimate for preparation. Always consult your midwife or doctor.

Часто задаваемые вопросы (FAQ)

How is a Pregnancy Due Date Calculated?

The standard method for calculating a pregnancy due date is Naegele's Rule: add 280 days (40 weeks) to the first day of your Last Menstrual Period (LMP). This is used by most healthcare providers worldwide.

The Three Trimesters

First Trimester (Weeks 1-12): Critical organ development. Morning sickness is common. The embryo becomes a fetus.
Second Trimester (Weeks 13-27): Often called the 'golden trimester.' Energy returns, baby movements begin (quickening), and sex can usually be determined.
Third Trimester (Weeks 28-40): Rapid fetal growth and preparation for delivery. Prenatal visits become more frequent.

Important Note

Only about 5% of babies are born on their exact due date. Most arrive within 2 weeks before or after. Your OB or midwife may adjust your due date after an early ultrasound for more accuracy.

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Last updated: April 3, 2026

Calculation Details

Due Date Result

Часто задаваемые вопросы (FAQ)

How is a Pregnancy Due Date Calculated?

The Three Trimesters

Important Note

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