Ovulation is related to the regular endocrine secretion of the ovaries, not to the days of menstruation. If the ovaries function normally, the hormones secreted by the ovaries can maintain a balance in the body, so that women can maintain a regular menstrual cycle, and the monthly menstrual cycle is once every 28-30 days, the ovulation day should be the 14th day before the next menstruation. If a woman’s menstrual cycle ends in 3 days, the ovulation day should be around the 10th day after the end of her menstrual cycle, because the endocrine secretion in a woman’s body is affected by many factors, such as work, mental tension, anxiety, excessive sadness, insomnia, etc., which can easily cause endocrine disorders in the body and lead to early or postponed ovulation. Ovulation may occur 5 days before and 4 days after the ovulation day. Ovulation may occur every day during the ovulation period, and even unexpected ovulation may occur during the safety period.