<p>Seismic increment of earth pressure during earthquake excitation is a key parameter in the seismic design of building basement walls. However, most previous studies have neglected the effects of soil–structure interaction and building inertia in evaluating seismic earth pressure. This study employs a direct numerical approach to simulate a building situated on a rigid rock base, with its basement walls embedded in the surrounding soil. A comprehensive parametric study was conducted to examine the influence of building and input motion characteristics on the seismic earth pressure under both rigid and compliant base conditions. Based on the results, a new analytical solution is proposed by extending previous approaches to account for rigid base conditions. The findings indicate that the normalized seismic thrust increases with the building’s height-to-depth and width-to-depth ratios, as well as with the peak ground acceleration and Arias intensity of the input motion. Moreover, the resultant seismic thrust acts approximately at mid-height of the wall. Comparative analysis confirms that the proposed solution achieves improved prediction accuracy compared to existing analytical models. Finally, a practical design procedure is presented to estimate the seismic earth pressure on basement walls under rigid-base conditions, providing a reliable and efficient approach for engineering applications.</p>