The neutralization of concrete usually results in material deterioration of a reinforced concrete (RC) bridge, so that the seismic capacity of the structure tends to degrade over time. This paper determined the deteriorated plastic hinge properties of the neutralized RC bridge column and performed the pushover analysis to obtain the decayed seismic capacity curves. As a result, the time-dependent fragility curves with respect to some representative damage levels can be established and the possible seismic loss can be expressed as a function of service time. In addition, a rapid seismic risk analysis system for the existing bridges based on the pre-calculated time-dependent fragility curves was established. This system can instantly estimate and visually demonstrate the level of damage to bridges due to a specific seismic event and the corresponding economic loss due to the damage of bridges. The S-surfaces representing retrofitting cost versus service time for a neutralized RC bridge subjected to different earthquake levels were determined quantitatively in a case study. Throughout the whole life-cycle of a bridge, critical service times corresponding to dramatically increased slopes in the S-surface associated with cost elevations can be identified to assist in the development of a financially optimized strategy for timely seismic retrofitting.