  Magnetocrystalline anisotropy, a crucial factor in magnetic properties and
applications like magnetoresistive random-access memory, often requires
extensive $k$-point mesh in first-principles calculations. In this study, we
develop a Wannier orbital tight-binding model incorporating crystal and spin
symmetries and utilize time-reversal symmetry to divide magnetization
components. This model enables efficient computation of magnetocrystalline
anisotropy. Applying this method to $\mathrm{L1_0}$ $\mathrm{FePt}$ and
$\mathrm{FeNi}$, we calculate the dependence of the anisotropic energy on
$k$-point mesh size, chemical potential, spin-orbit interaction, and
magnetization direction. The results validate the practicality of the models to
the energy order of $10~[\mathrm{\mu eV}/f.u.]$.
