This paper illustrates the effect of chloride-induced corrosion in the flexural capacity of a pretensioned concrete girder in an existing girder-and-slab deck bridge. The numerical study of the time-wise variation of the flexural capacity is based on a proposed model for the loss of cross-sectional area of the prestressing strands. It was observed that almost 46% of the total area of strands can get affected due to chloride-induced corrosion of the girder, by the end of its service life. The corresponding flexural capacity of the girder gets reduced by 50% of its initial capacity. © 2019, Springer Nature Singapore Pte Ltd.