The method of calculating the safe period is as follows: 14 days after ovulation, which is 14 days before the next menstrual period, is the day of ovulation. Using the day of ovulation as the standard, 5 days before and 4 days after is the ovulation period. For example, if the patient’s menstrual cycle is 30 days, then the 16th day of menstruation, is the day of ovulation, and the 11th to 20th day of menstruation is the ovulation period, during which the patient has the highest chance of ovulating. However, ovulation in women can be affected by various factors, such as changes in mood, increased stress at work and school or changes in the work and school environment, etc. All of these factors can affect ovulation in women. Therefore, ovulation can occur both during ovulation and during the safe period. If there is no intention of pregnancy, then it is advisable to use contraception at all times to avoid unwanted pregnancy.