The majority of existing buildings in any urban environment are self-styled buildings with varied construction practices. Most of the time these are built without any consideration for the seismicity of that location. Therefore become vulnerable building stock in case of any eventuality, paving the way for a disaster. The damages caused to buildings and the causalities resulted thereof during past earthquakes (Bhuj (2001), Sikkim (2011), Nepal (2015), Turkey (2023), etc.), are the epitome of this disaster. In view of this scenario, active research has been focused in this direction resulting in several updates of seismic provisions in order to provide a safe habitat. However, in order to visualize the vulnerability of existing buildings in comparison with the latest seismic provisions, the reliability of performance needs to be evaluated with code revisions. Hence, an attempt has been made to analyze the comparative reliability assessment of the performance of an existing building designed for more than a decades in accordance with IS:1893–2002 and IS:1893–2016 regulations. In the present study, the structural performance of the selected building has been evaluated in terms of the reliability index for the chosen limit state. Nonlinear static analysis is carried out to envisage the structural capacity and performance point of the building in accordance with IS:1893–2002 & 2016. From the analysis results it can be clearly emphasized that the reliability of existing building performance decreases with time. However, reliability of structural performance has shown significant increase with improved seismic regulations. Hence, the deficient structural components need to be repaired / retrofitted in accordance with latest codal provisions to ensure the structure to remain safe & functional.