Due Date Calculator

This calculator estimates your pregnancy due date using Naegele's rule — the standard obstetric method used worldwide. Enter the first day of your last menstrual period (LMP) and the calculator projects your estimated date of delivery (EDD), conception window, and trimester milestones.

Naegele's Rule

Due Date = Last Menstrual Period + 280 days (40 weeks)

The formula assumes a 28-day menstrual cycle with ovulation on day 14. Only about 5% of babies are born on their exact due date — the EDD defines a target window, not a fixed day.

Pregnancy Trimesters

First Trimester (Weeks 1–13): Organ formation, morning sickness common. Most miscarriages occur here.
Second Trimester (Weeks 14–27): Baby movement felt, anatomy scan typically at week 20. Generally the most comfortable phase.
Third Trimester (Weeks 28–40+): Rapid weight gain, baby assumes birth position, preparation for labour.

How Accurate Is This Calculator?

Accuracy depends on how regular your cycle is. Women with cycles shorter or longer than 28 days may have a due date that shifts by several days. An ultrasound scan at 8–12 weeks provides the most reliable dating and may revise the EDD.

Frequently Asked Questions

What if I don't know my LMP?

Your doctor will use an early ultrasound to estimate gestational age based on the baby's size — specifically crown-to-rump length (CRL) in the first trimester.

Is a 38-week delivery premature?

Babies born at 37–42 weeks are considered full-term. Births before 37 weeks are preterm. Your healthcare provider monitors growth and readiness regardless of the EDD.

Can I go into labour before the due date?

Yes. A typical pregnancy is anywhere from 38 to 42 weeks. The due date is the midpoint of a normal range, not an expiry date.