Breeding ratio (BR) and doubling time (DT) will become increasingly important indices as utilities and manufacturers seek to harness the breeder reactor. From these indices, it is possible to quickly sense the capability of a particular breeder reactor to produce more fuel than it uses. A set of definitions of BR and DT is proposed that appears well suited to overall fuel-cycle performance considerations. A key feature of these definitions is that BR is a value that is time averaged over one fuel cycle. A fuel cycle begins at the time of reactor startup after refueling and ends when the reactor is shut down for subsequent refueling. In addition, the determinations are based on all fuel in the core and blankets at the beginning and end of the fuel cycle, as contrasted to only those portions that are entering or leaving the reactor. Determining BR and DT in this manner gives results that are both accurate and consistent.