<p>This study focuses on the critical role of soil-structure interaction in seismic analysis and design, underlining its importance for the correct assessment of building performance under seismic loads. One-dimensional free-field analysis and SSI modeling using seven real earthquake records were conducted. The results show that fixed-base models considerably underestimate seismic responses on softer soils such as type D clay and type D sand. Results indicate that response spectra increase significantly with the depth of the soil, and type D soil shows the highest seismic amplification, up to 147%. SSI models further show lateral deflection amplifications of up to 107% for clay and 91.8% for sand, with inter-story drifts exceeding 94.6% and 89. 8% for clay and sand respectively, underlining the severe underestimation inherent in fixed-base models. The underestimated seismic responses in fixed-base models are 1.23–2.07 times lower than those predicted by SSI models, which clearly shows the urgent need to include SSI considerations in the current seismic design practices. However, this model is limited to RC frames on homogeneous soil profiles and does not account for layered soil effects. An empirical amplification factor was developed based on structural height and soil shear wave velocity, offering a simplified way to estimate SSI-modified displacements and fundamental periods. The study henceforth concludes that including the parameters of soil, such as stiffness, density, shear strength, and damping capacity, is very important in enhancing the safety and resilience of structures in seismically active regions. Current building codes poorly address the influence of SSI, posing very high risks, especially for structures on loose or soft soils. Therefore, adopting SSI-informed strategies is important for enhancing the reliability of earthquake-resistant designs and mitigating seismic risks.</p>