A simple economic analysis is proposed for light water reactor (LWR) in-core fuel management. Its final objective is the fuel cost. Using the discrete discounting technique with single payment costs, the fuel cost for one equilibrium cycle or a sequence of a number of nonequilibrium cycles may be determined. In this latter case, the costs are projected as groups of costs at the reference time. This technique is simplified by defining new economic factors, time scales, and burnup values. The fuel cost thus obtained is an average cost over the number of cycles considered. This analysis is written as a subroutine FULCOS suitable for absorption by short running computer codes that work the optimization problems for LWRs.