How to Calculate Due Date Backwards

Pregnancy is a wonderful and exciting time for new moms and dads. Finding out that you are pregnant can fill you with both excitement and fear, and knowing when your baby is expected to be born is one of the first things you will want to do. According to the American Pregnancy Association, the typical length of a normal pregnancy is 40 weeks. If you know the first day of your last normal menstrual cycle, you can calculate backwards to discover when you are due.

Instructions

    • 1

      Determine the first day of your last menstrual period. While you are not pregnant yet, the first two weeks after your period are considered the first two weeks of your pregnancy because these are the weeks that the egg is developing in preparation for fertilization.

    • 2

      Add seven days to the start date of your last period. So for example, if your last period was March 1, you will add seven days to end on March 8.

    • 3

      Count backwards three months to determine the due date. So for example, if your last menstrual period was March 1 and you added seven days to end on March 8, you will count back three months to end on December 8. December 8 will be your due date.

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