Estimating the remaining service life of reinforced concrete structures exposed to corrosion requires an approach that captures global structural behavior while avoiding the computational burden of conventional reliability methods. This study proposes a system performance based analytical–practical framework for service life prediction. First, the current condition of the structure is assessed through field tests, including determination of concrete and reinforcing steel strength, reinforcement corrosion rate, chloride ion penetration depth, and concrete cover thickness. A validated empirical model is then employed to predict corrosion progression and the time-dependent degradation of mechanical and geometric properties of structural members. An updated numerical model of the structure is developed, and a system performance index is defined based on the overstrength factor under gravity loading. Service life is estimated by tracking the degradation of this index and identifying the time at which it drops below the performance threshold. Application to an industrial cooling tower showed that the overstrength factor decreased from 1.08 at 40 years to 0.89 at 60 years, with functional end of life occurring at 47 years; thus, the remaining life at assessment was 7 years. A strengthening scenario demonstrated that targeted retrofit of critical members can significantly extend service life. The method is computationally efficient and supports rehabilitation decision-making.