Despite the recent surge in the construction of ballastless railway tracks, there exists a notable research gap concerning the rail seat load (RSL) associated with these track types. The RSL is the load transferred from the rail to the fastening system, the plate beneath the rail and the rail pad. The prediction of RSL in ballasted track systems is widely investigated, however, there has been a relative lack of research into the ballastless railway track systems. In this paper, a 2D finite element model (2D FEM) was adopted to evaluate the RSL concerning the effective parameters, including sleeper spacing, fastening system stiffness and the flexural modulus of the rail. The numerical model was validated through a field test performed in the study. Moreover, a mathematical expression was proposed to determine the RSL ratio for concrete slab tracks. The RSL directly correlates with the sleeper spacing and the fastening stiffness, while this relation with the flexural rigidity is inverse. Based on the results, it was found that the RSL ratio obtained from the conventional methods differed considerably from the proposed mathematical expression. More specifically, this difference was observed in almost all of the values in the sleeper spacing and flexural rigidity of rail for the Kerr model except 0.68 m and 5 MN.m2, respectively.