How to calculate how many weeks pregnant is calculated by counting from the first day of the last normal menstrual period, 7 days for a week. Alternatively, an ultrasound is used to extrapolate the weeks of pregnancy. How long is pregnancy can be expressed in terms of full days or weeks because it is difficult for a pregnant woman to determine the exact date of pregnancy, so medically, the expected date of delivery should be from the first day of the last period. The full duration of pregnancy is 280 days or 10 gestational months. In the case of regular menstrual cycles, the gestational week is estimated from the last menstrual period, with the last vacation day plus 9 days or minus 3 days as the expected month, plus 7 days as the expected cut-off date. In case of irregular menstruation or forgetfulness of the last period, the week of pregnancy can be determined by ultrasonography, and in some cases of IVF, it depends on the time of transferring the embryo and a few days of the blastocysts to determine the last period. Patients are advised to go to maternity hospitals or obstetrics and gynecology departments of regular hospitals for relevant consultation and examination, and to scientifically and reasonably project the week of pregnancy under the guidance of professional doctors, so as to avoid the occurrence of overdue pregnancy.