This study’s intention is to investigate the seismic effects on the cantilever balcony (slab) of fifteen-storied (G + 14) rectangular and C-shaped buildings through time-history analysis (THA). For this purpose, to match the target ground motion, considering soft soil and oblique-slip parameters, six-time history functions are used. The buildings are separately modeled with cantilever balconies along the longer edges comprising three types of cases that are balconies on all floors, on even floors and on odd floors. The seismic zone for the specified buildings is taken as Zone V as per the Indian Standard. The buildings under consideration are analyzed with time-history analysis (THA) using ETABS, and the results are evaluated and discussed, focusing primarily on the deflection of the balcony for each type to define the most effectual size of the cantilever balcony for each set of configurations, and the optimum sizes of the cantilever balcony are recommended. The recommended optimum sizes of cantilever balcony help in providing a safe balcony on the respective floor in each case under consideration of the two case-study buildings. © 2023, Springer Nature Switzerland AG.