The room-temperature magnetic susceptibility anisotropy of eight-coordinate lanthanide ions was modelled numerically for polyhedra resulting from distortions of the regular cube to a tetragonal prism, antiprism, and dodecahedron. Our aim is to illustrate how the magnitude and sign of the room-temperature magnetic anisotropy can be related to the shape of the coordination polyhedron and to estimate its maximum value. Tb(III), Dy(III), and Tm(III) ions are found to have the largest values of the magnetic anisotropy in all coordination polyhedra. These results are helpful to rationalize the orientational behavior of lanthanide-containing liquid crystals in an external magnetic field.