The algorithm of the expected date of delivery is based on the time of the last menstrual period. If the pregnant woman usually has regular menstruation, the date of the last menstrual period should first be determined, i.e., the first day of the last menstrual period of the pregnant woman, the month “-3” or “+9” is the month of the expected date of delivery, and the number of days “+7 ” is the number of days to the expected date of labor. If a pregnant woman has irregular menstrual cycles in the past or does not remember the date of her last menstrual period, the week of pregnancy and the expected date of labor can be determined by taking into account the time when the early pregnancy reaction occurs, the time when the fetal movement occurs, or the ultrasound in early pregnancy. Early pregnancy reaction usually appears around 6 weeks of pregnancy; fetal movement can be felt around 16 to 20 weeks of pregnancy. In addition, the size of the fetal buds in the early pregnancy ultrasound can also be used to calculate the week of pregnancy, and the length of the fetal buds or the length of the head and buttocks +6.5 is the week of pregnancy. After calculating the actual week of pregnancy, the date of the last menstrual period and the expected date of delivery will be calculated.