If the usual menstrual cycle is 30 days and the period is 7 days clean, the chance of getting pregnant by having intercourse on the 7th day of cleanliness is very high because the date of ovulation is 14 days before the next menstruation. So when you have intercourse on the 14th day of your period, the sperm will enter your body and can survive for 2-3 days, where it will wait for the egg when it reaches the fallopian tube, and after ovulation the sperm and egg will combine to form a fertilized egg and you will get pregnant. If you are planning to get pregnant, you can choose to have intercourse during ovulation and your chances of getting pregnant will increase. If you are not planning to get pregnant, it is important to use birth control when having intercourse during ovulation to avoid pregnancy.