The normal calculation of the physiological cycle is the time between the first day of menstruation is called the physiological cycle, which is usually 25-35 days, within the range of normal. If it is shorter than 25 days, it is called a short menstrual cycle, which often causes anemia; if it is longer than 35 days, it is called a long menstrual cycle, which requires high vigilance for ovarian insufficiency or luteal atrophy, etc. Therefore, the normal calculation of the physiological cycle is very crucial to determine the disease.