The process of rupture of a mature follicle from the ovary into the fallopian tube is called ovulation. In normal women of childbearing age, ovulation occurs every 28 days or so, and the egg survives for 24 hours. However, the time of ovulation varies with each person’s health condition. For women with normal menstrual cycles, ovulation usually occurs two weeks before the start of the next period. If her menstrual cycle is 28 days, her ovulation day may be the 14th-15th day of her menstrual cycle, if her menstrual cycle is 30 days, her ovulation day is the 16th-17th day of her menstrual cycle, and if her menstrual cycle is 40 days, her ovulation day may be around the 25th day of her menstrual cycle. When a woman’s life rhythm and routine change, it will cause her endocrine situation to be affected by endocrine disorders, showing menstrual irregularities, and her period may be early or late, then the ovulation day will change with the change of her period. In addition, women who have irregular menstrual cycles or suffer from gynecological diseases may have their periods without ovulation, which causes their ovulation day cannot be estimated normally.