What is a safe period calculator? The safe period calculator is a tool for calculating menstrual cycles and safe periods. By entering the start date of the last menstrual period, you can calculate the approximate time of the next menstrual period and help women determine their menstrual cycle based on the menstrual cycle. safety period. Without contraceptive measures, it is less likely to get pregnant if you have sex during the safe period. How to determine the menstrual cycle. The calculation of a woman’s menstrual cycle is from the date of the last menstrual period to the date of the next menstrual period. It is usually 28 days, but some women