Magnetic anisotropy refers to the directional dependence of the magnetic properties of a system. It originates from the interaction between spin and orbital angular momenta, giving rise to spin-orbit coupling and zero-field splitting. Magnetic anisotropy can be classified as either easy-axis or easy-plane, depending on whether the magnetization preferentially aligns parallel to a certain axis (conventionally the z-axis) or lies within a plane perpendicular to it. The energy that orients the magnetization along this direction of easy magnetization is known as the magnetic anisotropy energy (MAE). For Co/Mg(O)(001), we determined the MAE by performing self-consistent, non-collinear PBE and PBE+U calculations with spin-orbit coupling for different magnetization orientations. The MAE was computed as the energy difference