A mass transit system of a transit authority automatically determines and applies the lowest possible transit fare to a patron's account, thereby releasing the patron from decisions leading to the most cost effective fare instrument for his or her transit pattern. A fair fare system and method utilizes the transit authority's existing hardware infrastructure, i.e., mainframe, vendors, gates, smart card and Point of Issue (POI) devices, with additional processing mechanisms for determining the best fare over rolling time periods. Because a relatively large storage capacity of the fare instrument is required, smart cards are employed for use with the fare fair system.