Expected date of delivery (Edd)- How is your baby’s due date calculated?

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Expected Date of Delivery (EDD): How Is Your Baby’s Due Date Calculated?

By Dr. Anuradha Narayanan

Consultant Obstetrician & Gynaecologist | Anurag Women Health Care, Chembur, Mumbai

Congratulations! You’re Pregnant!

One of the first questions every expecting mother asks is:

“When is my baby due?”

The Expected Date of Delivery (EDD), also known as the due date, is an estimated date when your baby is likely to be born. While it provides a helpful timeline for monitoring your pregnancy, only a small percentage of babies actually arrive on their exact due date.

Let’s understand how the due date is calculated and why it may change during pregnancy.

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What Is the Expected Date of Delivery (EDD)?

The EDD is the estimated day when your pregnancy reaches 40 weeks (280 days) from the first day of your last menstrual period (LMP).

Pregnancy is divided into three trimesters:

* First trimester: 0–13 weeks

* Second trimester: 14–27 weeks

* Third trimester: 28–40 weeks

A pregnancy is considered:

* Full term: 39–40 weeks

* Early term: 37–38 weeks

* Late term: 41 weeks

* Post-term: 42 weeks or more

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How Is the Due Date Calculated?

1. Using Your Last Menstrual Period (LMP)

This is the most common method for women with regular menstrual cycles.

Doctors use Naegele’s Rule:

* First day of your last period

* Add 1 year

* Subtract 3 months

* Add 7 days

Example

LMP: 10 January 2026

EDD = 17 October 2026

This calculation assumes a regular 28-day menstrual cycle with ovulation occurring around day 14.

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2. Early Pregnancy Ultrasound

If you’re unsure of your LMP or have irregular periods, an ultrasound provides the most accurate estimate.

An ultrasound performed between 8 and 13 weeks measures your baby’s Crown-Rump Length (CRL) and can accurately estimate the gestational age.

This method is especially useful when:

* Periods are irregular

* LMP is unknown

* Conception occurred after fertility treatment

* There is a significant difference between LMP and ultrasound dating

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3. IVF or Fertility Treatment

For pregnancies conceived through IVF or assisted reproduction, the due date is calculated using:

* Embryo transfer date

* Age of the embryo at transfer

This provides a highly accurate EDD.

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Can My Due Date Change?

Yes.

Your doctor may revise your due date if:

* Your menstrual cycles are irregular.

* Your early ultrasound differs significantly from your LMP calculation.

* Ovulation occurred earlier or later than expected.

Once confirmed during the first trimester, the due date usually remains unchanged.

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How Accurate Is the Due Date?

Your due date is only an estimate.

Research shows:

* Only about 5% of babies are born on their exact due date.

* Most healthy pregnancies deliver between 37 and 42 weeks.

* Many first-time mothers naturally deliver after their due date.

Every pregnancy is unique.

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Why Is the Due Date Important?

Knowing your EDD helps your obstetrician:

* Monitor your baby’s growth

* Schedule important scans

* Plan blood tests

* Monitor fetal movements

* Detect growth restriction

* Decide the best timing for delivery if complications arise

* Identify post-term pregnancy

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Important Milestones During Pregnancy

6–8 Weeks

* Pregnancy confirmation

* First ultrasound

11–13 Weeks

* NT scan

* First-trimester screening

18–22 Weeks

* Detailed anomaly scan

24–28 Weeks

* Gestational diabetes screening

28–36 Weeks

* Growth scans (if indicated)

* Vaccinations

* Birth planning

36–40 Weeks

* Weekly check-ups

* Monitoring baby’s position

* Planning labour and delivery

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What If I Cross My Due Date?

Many pregnancies continue safely beyond the due date.

Your doctor may advise:

* Fetal movement monitoring

* Non-stress test (NST)

* Ultrasound with amniotic fluid assessment

* Doppler studies (if needed)

* Induction of labour if medically indicated

The goal is always the safest outcome for both mother and baby.

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Common Questions

Can I calculate my due date at home?

Yes. Many online calculators use your LMP to estimate your due date, but an early pregnancy ultrasound is often more accurate.

My periods are irregular. Will my due date be wrong?

Not necessarily. Your doctor will rely more on an early ultrasound to determine the correct gestational age.

Can stress or exercise change my due date?

No. Normal physical activity and stress do not change the baby’s due date.

Is it normal to deliver before or after the due date?

Yes. Most babies are born within two weeks before or after the expected date.

Your Expected Date of Delivery is an important guide, but it is not a fixed appointment. Every baby follows its own timeline. Regular antenatal check-ups, timely ultrasounds, and close communication with your obstetrician help ensure a healthy pregnancy and safe delivery.

Rather than focusing on one specific day, think of your due date as the beginning of the exciting period when you are most likely to meet your baby.

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Looking for Expert Pregnancy Care in Chembur, Mumbai?

At Anurag Women Health Care, we provide comprehensive antenatal care, fetal monitoring, high-risk pregnancy management, pregnancy scans, and personalized birth planning to support you throughout your pregnancy journey.

Book your antenatal consultation today and let us help you achieve a healthy pregnancy and safe delivery.