The calculation of menstruation, or the calculation of a woman’s menstrual cycle, is usually calculated from the first day of the first period to the first day of the next period. Most women have a menstrual cycle of 21-35 days, with an average of 28 days. Early arrival or delay within a week is normal, mostly due to appropriate hormonal changes in ovarian secretion. In the first 2-3 years of menstruation, women may have unstable menstrual cycles, and after 2-3 years, most women will have normal menstrual cycles. Women should pay attention to proper rest and regular life, avoid staying up late and straining to keep their menstrual cycle regular, otherwise it is easy to lead to early or delayed menstruation. In short, during menstruation, women should pay attention to avoid cold stimulation and strain, eat more hot food, and also maintain the hygiene of the vulva.