The paper presents a comparison analysis between numerical method and nonlinear mathematical model for the prediction of the vertical motions of a double stepped planing hull in regular wave. The numerical method is to Unsteady Reynolds Averaged Navier-Stokes (URANS) equations solution via moving mesh techniques (overset/chimera), performed at different model speeds, wavelengths, and wave heights using the commercial software Siemens PLM Star-CCM+. Instead, the analytical solution is obtained using nonlinear mathematical model. The presented non-linear mathematical model is developed using a combined approach based on 2D+T theory, momentum theory, and linear wake profile. Under such assumption, the double stepped planing hull is divided into three planing surfaces, and hydrodynamic forces acting on each planing surface is found by extension of simulation of symmetric water entry of two-dimensional wedge section bodies. Then, each sub-problem is solved by extending the mathematical simulation of wedge penetrating water. Final vertical force and pitching moment are found and substituted in motion equation. The mathematical model is able to compute heave and pitch motion in calm water and regular waves. Results of numerical method and novel 2D+T analytical method are compared against each other.