The safe period method of contraception is a method that does not use any drugs, tools or surgery, but follows the natural physiological laws of the human body, using the different natural signals produced by the physiology of a woman’s menstrual cycle to identify the “fertile” or “less fertile” period of her menstrual cycle. The method uses different natural signals in a woman’s menstrual cycle to identify the “fertile” or “infertile” phase of her menstrual cycle, so that she can choose the date of her sexual life to achieve the purpose of contraception. The first step in using the safe period method of contraception is to determine the ovulation period, based on basal body temperature, cervical mucus or the regularity of the menstrual cycle. Most women have a menstrual cycle of 28 to 30 days and are expected to ovulate 14 days before their next period. The egg can survive for 1 to 2 days after ovulation, while fertilization is strongest within 24 hours after ovulation. Sperm can survive for 3 to 5 days after entering the female reproductive tract. Therefore, 4-5 days before and after ovulation are the fertile period. The days before and after the day of ovulation and the 5 days before and after the day of ovulation are the “period of unlikely conception”. This is also known as the safe period. However, the ovulation process can be delayed or advanced due to factors such as life, emotions, sex, health conditions and the external environment, and additional ovulation can occur. Therefore, safe period contraception is not very reliable, and the failure rate is about 20%.