Due date is the date when a pregnant woman is expected to give birth. Due date is not the exact date of delivery. Scientists have calculated that only about 53% of women give birth on the due date. Since it is difficult for every pregnant woman to accurately determine the time of conception, medical regulations stipulate that the due date is calculated from the first day of the last menstrual period. The entire pregnancy period is 280 days, 10 gestation months (each gestation month is 28 days).