Women\’s Safe Period Calculation Table Women\’s menstrual cycle has a vital impact on health and fertility. However, many women do not understand their menstrual cycles and therefore cannot make scientific and accurate predictions about their menstrual periods. Below, we will introduce the calculation and prediction methods of menstrual cycle from four aspects to help women understand their bodies and stay safe and healthy. Aspect 1: What is the menstrual cycle? The menstrual cycle refers to the period between the first day of a woman’s menstrual cycle and the first day of her next menstrual period.