To determine how long you are pregnant, you can project according to the woman’s menstrual cycle, or ultrasound examination to clarify, as follows: 1, according to the menstrual cycle projection: for women with regular menstrual cycles, you can use menstruation to project the time of pregnancy. The number of days a woman is pregnant is not calculated from the time of intercourse, but according to the first day of the last menstrual period, from the first day of the last menstrual period to the date of the day of the pregnancy test that is the number of days of pregnancy, this method in the clinic is an agreed algorithm; 2, ultrasound: if a woman does not remember the last menstrual period or irregular menstrual cycle, ovulation is not normal, you can determine the number of days of pregnancy through ultrasound. Clinically, the size of the fetal buds is checked by ultrasound, and the length of the buds (in cm) + 6.5 is the week of pregnancy on the day of the examination for approximate estimation. Even for women who have regular periods, the week of pregnancy will be reconfirmed by referring to the ultrasound of early pregnancy. It should be reminded that ultrasound should be done as early in the pregnancy as possible, i.e. before 12 weeks, as this calculation is not so accurate in the later stages due to the development of the baby. Knowing the number of days pregnant has more benefits, can be on time to the hospital for prenatal checkups, but also can help to predict the expected date of delivery. It is important to note that the number of days of pregnancy is not particularly accurate and that there is a difference between the actual number of days of pregnancy and the number of days on the ultrasound, which is normal as long as the difference does not exceed 1 week (which is within the permissible margin of error).