The due date should be calculated according to the time of the last menstrual period. If you are pregnant in May, the due date will be in February/March next year. For women with regular periods, the formula for calculating the due date is the first day after the last menstrual period, according to the month plus 9 or minus 3, and the date plus 7. If you have irregular periods, you cannot calculate the due date according to the time of your period, but according to the size of the gestational sac measured by ultrasound at your first delivery. Since the due date is the approximate date of birth calculated according to the last menstrual period, it is normal to give birth 1-2 weeks earlier or later than the due date, and it is necessary to do pregnancy tests regularly in order to know the development of the fetus. Pay attention to increase nutrition and take appropriate calcium and vitamin supplements to ensure the nutritional needs of the fetus and promote fetal bone development.