How to Calculate an Estimated Date of Delivery

Pregnancy is typically around nine months, or 40 weeks, in length. This means that most women can count nine months from the first month of pregnancy to learn when the baby is due to arrive. However, figuring out a more specific date of delivery, called the due date, takes a little more information. One of the most useful tools when determining a woman's due date is the to identify the first day of the last menstrual period. Consult a doctor with any questions or concerns about pregnancy.

Things You'll Need

• Calendar
• Calculator
• Computer access
• Ultrasound

Show More

Instructions

• 1

  Identify the date of the first day of the last menstrual period, if possible. Using a calendar, count 40 weeks (the average length of a pregnancy) from that date. This is the estimated date of delivery, or due date.

• 2

  Visit websites that offer due date calculators, such as iVillage.com, BabyCenter.com, and What to Expect.com. Have the date of the last menstrual period on hand, if known, or the date of conception, if that information is known. Enter the date in the tool on the website of your choice and click calculate. The tool will then provide you with an estimated pregnancy due date. If you know the date of conception (usually 2 weeks after the first day of the last menstrual period) and this option is available on the website, enter this into the correct fields and click calculate. A due date will then be tabulated.

• 3

  Request an ultrasound if the last menstrual period date is unknown or if your menstrual cycles are very irregular. An ultrasound can measure the actual size of the fetus, which means that a healthcare professional can identify the current stage of pregnancy and provide an estimated due date based on that information.