The propagation of cosmic rays through the heliosphere is solved for more than half a century by stochastic methods based on Ito’s lemma. This work estimates the statistical error of the solution of the Fokker–Planck equation by a 1D forward stochastic differential equations method. The dependence of the error on simulation statistics and energy is presented for different combinations of input parameters. The 1% precision criterion in intensities and 1% criterion in standard deviation are defined as a function of the solar wind’s velocity and the diffusion coefficient value.