For women with normal menstrual cycles, ovulation usually occurs about 14 days before the next menstrual cycle. If the menstrual cycle is irregular and the date of the next period is not easy to predict, the 15th day after the current period can be roughly projected as the day of ovulation. Ovulation is often related to factors such as environment, emotions, physical health, sexual life, and use of birth control pills, etc. Sometimes ovulation can be early or two eggs at once, and sometimes ovulation can be delayed or suspended. Therefore, it is sometimes not possible to determine the date of ovulation simply by projecting the menstrual cycle. In this case, the Billings method can be applied to observe cervical mucus and predict the date of ovulation. This method can be used for contraception as well as for conception. The method is as follows: each night before going to bed, wipe the vaginal opening with toilet paper (taking care not to wipe the inside of the vagina), observe the transparency, amount and degree of straining of the mucus on the paper, and record the sensation in the vulva. The slippery sensation may last anywhere from 2 or 3 days. The last day of this slippery sensation is called the “peak mucus day”. This day occurs on average 0.9 days before ovulation. Billings considers the period from the first day of the menstrual cycle to 3 days after the “peak mucus day” as the fertile period and the rest as the safe period. This method of predicting the day of ovulation by observing cervical mucus and vulvar sensation is known as the Billings Method of Natural Contraception. The study showed that the probability of conception during intercourse was 0.667/cycle on the peak day, 0.444/cycle on the first day after the peak day, 0.205/cycle on the second day, 0.089/cycle on the third day, and 0.004/cycle during the safe period.