Pregnancy lasts an average of 40 weeks (280 days) from the first day of your last menstrual period. To calculate your due date, enter the first day of your last menstrual period, then click "Calculate." Normal pregnancies vary in length, so think of your due date as approximate. Most babies are born from two weeks before to two weeks after the due date. If you cannot remember the date of your last menstrual period, your doctor will use other methods to determine your due date.
