Pregnancy Due Date Calculator

How Is the Due Date Calculated?

The estimated due date (EDD) is calculated by adding 280 days (40 weeks) to the first day of your last menstrual period (LMP). This approach, known as Naegele's Rule, is the most widely used method by obstetricians and gynecologists worldwide.

The Three Trimesters of Pregnancy

First trimester (weeks 1-12): Major organ formation. Second trimester (weeks 13-26): Rapid growth and first movements. Third trimester (weeks 27-40): Final maturation and preparation for birth.

What Are Gestational Weeks?

Gestational weeks are counted from the first day of the last menstrual period, not from conception. This means that during the first two gestational weeks, fertilization has not technically occurred yet.

Frequently Asked Questions

Is the estimated due date accurate?

Only about 5% of babies are born on the exact EDD. It is normal for delivery to occur between weeks 38 and 42. A first-trimester ultrasound can refine the date with greater precision.

What if I don't remember my last period date?

In that case, your doctor can estimate the gestational age through an ultrasound by measuring the size of the embryo or fetus.