Girls safe period calculation method is particularly simple, refers to the first day of menstruation seven days before and after eight days, such as 10 days to menstruation, the safe period is between 3-18 days, due to this time belongs to the luteal phase and follicular phase, generally no eggs discharged, and therefore do not take contraceptive measures to cohabitate with the case of its chances of pregnancy is very low. But a small number of women in the safe period in the process of intercourse, will be due to the stimulation of sexual excitement and induce abnormal ovulation caused by unwanted pregnancy, so the safe period of contraception is not absolutely safe, it is recommended that men wear condoms, or women oral short-acting contraceptives for contraception.