Abstract: A fertility indicator for storing a plurality of time measurements between consecutive menstrual periods by using a plurality of hours as a unit of count to optimize time measurements and output displays. The indicator uses a computer to analyze the menstrual cycles variables, by applying the Ogino's method and in combination with ovulation cycle variables, to project the fertile status for the present cycle, and by treating all of the stored cycles as the length of the present cycle, the fertile extensions are a true representation of user's cycle history in an ever renewing state as new data erases the oldest stored data. Arrangements are provided for data input protection and data retention.