Abstract: A calculating device is provided to aid in predicting the periods of fertility and non-fertility during a menstrual cycle of a user. The device includes a first disc having indicia thereon representing the calender days of the present month and the next month, a second disc having indicia thereon indicating the length of and the days in a normal menstrual cycle of the user, and a base plate having markers thereon which, when placed in proper registry with the indicia on the two discs, indicate which calendar days during the present menstrual cycle the user is fertile. In a second embodiment an additional disc is provided for indicating days in the shortest period of a user who has irregular menstrual cycles. This additional disc, when placed in registry with the other discs, indicates an expanded period of fertility for the user.