If a woman’s last menstrual period was on March 17th, her due date will be December 24th. The due date is calculated by taking the first day of the last menstrual period, adding 9 or subtracting 3 from the month, and adding 7 to the day. A pregnancy usually lasts 40 weeks, so if your last menstrual period was on March 17th, you can calculate your due date to be December 24th by using the above method. The expected date of labor is only a rough estimate and will vary somewhat from the actual number of days of labor. In addition, for women with irregular menstruation, the date of ovulation is less certain, and using the method of menstruation to calculate the expected date of labor may not be accurate enough. When you find out that you are pregnant, you can go to the hospital for medical treatment, and with the help of a professional doctor, you can determine the time of the expected date of delivery more accurately by taking some lengths of the fetus’s body.