How to Calculate a due Date by the Number of Weeks Pregnant

One of the most common questions you'll be asked as a pregnant woman relates to your little one's arrival: What's your due date? Even though data from the American Pregnancy Association shows that only 5 percent of babies end up being born on their due date, knowing your baby's due date helps you and your loved ones plan for your little one's arrival. Calculating your due date by the number of weeks pregnant is a simple technique that requires a calendar.

Things You'll Need

  • Calendar

Instructions

    • 1

      Find the date on your calendar that corresponds to your nearest even week of pregnancy. For example, if you'll be 12 weeks pregnant on April 10 and today's date is April 8, then you need to select April 10. Circle this date and write your number of weeks pregnant on it (12 weeks, in this case).

    • 2

      Verify your number of weeks pregnant. Starting with the circled date, count back your number of weeks pregnant on your calendar. For instance, if you're 12 weeks pregnant on April 10, you should count back 12 weeks from that date, which would give you January 16. If you've kept records on your menstrual cycle and know your number of weeks pregnant based on this information, then this date should also be the first day of your last menstrual period (LMP). If you have no records on your LMP and your doctor had to date your pregnancy using an ultrasound, make sure this date corresponds with the date your doctor gave you to mark the beginning of your baby's gestational age.

    • 3

      Subtract your number of weeks pregnant from 40 to get the number of weeks that you have left in your pregnancy. For instance, if you're 12 weeks pregnant, subtract 12 weeks from 40 weeks which gives you 28 weeks. You have 28 weeks left in your pregnancy until your estimated due date.

    • 4

      Count forward on your calendar the number of weeks that you have left in your pregnancy. For instance, if you have 28 weeks of pregnancy left on April 10, then counting forward 28 weeks gives you an estimated due date of October 23 of that same year.

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