Many IVF patients are curious about how to calculate the gestational week of pregnancy in IVF and whether it is the same as in natural conception. First of all, we should understand how the gestational week is calculated in patients who conceive naturally. For a naturally conceived patient, the first day of the last menstrual period is the first day of the gestational week, not the day of fertilization, which is the beginning of the gestational week. Therefore, according to this calculation, a patient with a 28-day menstrual cycle may be counted as 14 days at the time of fertilization. Also, the common way to calculate the due date is to calculate the month of the last menstrual period minus 3 months or plus 9 months and the date plus 7 days. The date of transfer is certain for IVF patients. Since the various protocols of ovulation promotion and endometrial preparation before transfer change the patient’s menstrual cycle, the time of the last menstrual period for IVF patients is calculated based on the day of transfer and the number of embryonic days. Specifically, if a D3 embryo is transferred, the last menstrual period is the transfer date minus 17 days, and if a D5 blastocyst is transferred, the last menstrual period is the transfer date minus 19 days. Once the last menstrual period is determined, the gestational week is counted from the calculated last menstrual period, and the due date is determined in the same way as for natural conception patients: the calculated last menstrual month minus 3 months or plus 9 months and the date plus 7 days. In addition to this, in patients with natural cycle transplantation, the menstrual cycle is not artificially altered, and the calculation of the gestational week and the expected date of delivery is based on their real last menstrual period. The correct calculation of the gestational week facilitates the observation and evaluation of the pregnancy and helps the obstetrician to correctly manage the various conditions of the pregnant woman. However, the pregnancy situation of pregnant women is very complicated and the development of the fetus may vary in the same pregnancy week, therefore, pregnant women should follow the advice of their doctors and have regular maternity checkups.