In general, pregnant women who are just pregnant do not know how to calculate how many days they are pregnant, which is very normal, how to know how many days pregnant methods are as follows: In general, pregnant women who are just pregnant want to use the day of intercourse to count, because intercourse means the union of sperm and egg cells, the starting point of the fetus, but in fact, this method is difficult to remember the time of intercourse, so it is not accurate. We commonly count from the first day of the last menstrual period, for example, if the first day of the last menstrual period is February 5th, and if you find out you are pregnant on March 20th, the number of days of pregnancy is forty-five days. For women who have regular periods, subtracting fifteen days from this method is the true time of conception. Another method is ultrasound. If you forget the exact time of your last menstrual period, you can use a later ultrasound to determine the exact number of days of pregnancy by examining the size of the fetus, the earlier ultrasound may not be very accurate in predicting the time of fetal conception, but the 4D ultrasound and Down screening ultrasound results are very accurate. It is important to go to the hospital regularly for checkups during pregnancy to avoid any special conditions that may affect the health of the pregnant woman and the fetus.