Baby Due Date Calculator: Estimating Your Delivery Date

While no one can predict with 100 percent certainty the date your baby will be born, there are formulas that will give you an estimate. In 1838, Dr. Franz Karl Naegele (1778-1851), a German obstetrician, developed a formula that estimated a woman's date of delivery based on the first day of her last menstrual period, an average 266-day gestation length (or 280 days from the date of the last menstrual period) and the assumption that a woman ovulated on day 14 of her menstrual cycle.

Things You'll Need

• Calendar

Show More

Instructions

• 1

  Determine the date of the first day of your last menstrual period.

  Example: January 1, 2011 = date of your last menstrual period

• 2

  Add seven days to that date.

  Example: January 1 + 7 days= January 8

• 3

  Subtract three months from that date and adjust the year, if necessary.

  Example: January 8 -- 3 months= October 8

  Estimated date of delivery (EDD), or due date = October 8, 2011