This study investigates the technique of variational calculus applied to estimate the slope stability considering the mechanism of planar failure.The critical plane failure surface should be determined because it theoretically indicates the most unfavorable plane to be considered when stabilizing a slope to rectify the instability generated by several statistically possible planes.This generates integrals that can be solved by numerical methods,such as the Newton Cotes and the finite differences methods.Additionally,a system of nonlinear equations is obtained and solved.The surface of the critical planar failure is determined by applying the condition of transversality in mobile boundaries,for which various examples are provided.The number of slices is varied in one of the examples,while the surface of the critical planar failure is determined in the others.Results are compared using analytical methods through axis rotations.All the results obtained by considering normal stress,safety factors,and critical planar failure are nearly the same;however,in this research,a study is carried out for“n”number of slices using programming methods.Sub-routines are important because they can be applied in slopes with different geometry,surcharge,interstitial pressure,and pseudo-static load.