Rehabilitation cycle is being studied in relation to life-cycle costing based on the realization that making rehabilitation cost-effective would require minimizing the necessary investment. However, the progress of an actual structure's deterioration cannot be predicted precisely without a collection of inspection data, and therefore, at present the rehabilitation cycle is merely calculated on the idealized progressive deterioration hypothesis. In this study, the optimal life cycle of reinforced concrete deck slabs is derived from the residual life determined through a series of fatigue experiments on deck slabs cut out from existing bridges and rehabilitated afterwards. As a result, precise and cost-effective rehabilitation planning was made possible.