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Pregnancy Due Date

Estimated due date.

About the Pregnancy Due Date

Estimated due date.

How is Due Date Calculated?

The standard method for calculating a due date is Naegele's Rule. It adds 280 days (40 weeks) to the first day of your Last Menstrual Period (LMP). Even though conception usually happens about two weeks after your LMP, doctors use the LMP because it is a more reliable confirmed date.

Trimesters Explained

Your pregnancy is divided into three distinct stages:

  • First Trimester (Weeks 1-12): The baby's body structure and organ systems develop. Most miscarriages occur during this period.
  • Second Trimester (Weeks 13-26): Often called the "honeymoon phase" as nausea subsides. You may feel the baby move for the first time.
  • Third Trimester (Weeks 27-40): The baby gains weight rapidly to prepare for birth. You may feel more fatigue.

Is the Due Date Accurate?

Only about 5% of babies are born on their exact due date. It is perfectly normal to give birth anywhere from two weeks before to two weeks after your estimated date. The calculated date is simply a midpoint guide for tracking development.