Abstract: A forecasting system takes advantage of an E-mail system of the internet to forecast different days of a following menstruation period of a woman via different terminals, such as a mobile telephone which supports WAP and a personal computer which is capable of connecting with the internet. The working of the forecasting system includes entering via a terminal relative information of menstruation of a woman, establishing a data base in a data server of the internet depending on the entered information, calculating an ovulation day, impregnable days, starting and ending days of a following menstrual flow of the woman, and sending out inquired forecast information to the woman via the different terminals.