A 15-day shortening of the interval between menstrual periods, i.e., the onset of menstruation 15 days earlier, may be caused by ovulatory bleeding or may be due to uterus-related diseases. After ovulation, there is a short transient drop in estrogen levels, and a small amount of endometrial shedding may occur, resulting in a small amount of vaginal bleeding. Ovulation occurs in the middle of menstruation, usually on the 14th day before the next period, so menstruation 15 days early may be ovulation bleeding, as long as the bleeding is small are physiological phenomena. If the menstrual period comes 15 days earlier and the bleeding is heavy, it may be abnormal uterine bleeding, which should be differentiated from ovulation bleeding. Patients are advised to go to the hospital for timely examination to determine whether the bleeding is caused by endometrial polyps, submucosal fibroids, etc., and if necessary, screening for cervical cancer is feasible. Therefore, menstruation 15 days early may be a physiological phenomenon, or it may be caused by related diseases, patients should pay attention to identify and pay attention to.