It takes half a month after intercourse to check if you are pregnant. If sperm and egg combine to form a fertilized egg after intercourse, you are pregnant. It takes some time for the human chorionic gonadotropin in the body to rise after pregnancy, and it takes about half a month after intercourse and conception for the human chorionic gonadotropin level in the body to increase significantly, and only when the blood HCG is checked may it show positive, and the blood HCG after pregnancy can be the earliest check to see if you are pregnant. After sexual intercourse, if the menstruation is delayed for a long time and does not come, it may be pregnant. When the menstruation is delayed for more than a week and does not come, you can check to see if you are pregnant. In early pregnancy, the blood HCG test is more accurate and can also check whether you are pregnant earlier, while the ultrasound needs to be about forty days pregnant before the echo of the pregnancy sac can be seen.