A normal woman’s period clears in three to seven days on average, taking the average of the middle, and clears in five days, so it is not safe if the eighth day after it clears just in time for ovulation. If you have sex during ovulation, it is likely to cause pregnancy, so the eighth day after menstruation is clean is the danger period. It is recommended that in clinical practice, if a safe period is calculated, it can only be calculated if the menstrual cycle is regular, otherwise it is not safe to speak of a safe period. Under normal circumstances, if the menstrual cycle is regular, the ovulation time is fourteen days before the next menstruation, according to this to calculate the ovulation period, four days before and three days after the ovulation day is the ovulation period, if you have intercourse during the ovulation period, the chance of pregnancy is very high.