A simple procedure is presented for computing optical transmission and Faraday‐rotation optical density (OD) planar layered structures when all internal reflections are taken into account. The procedure makes use of the Mueller matrix technique and assumes that interference effects, Faraday ellipticity, and boundary magneto‐optical effects, e.g., Kerr effect, are not important. The general formulas are applied to the case of the three‐layer structure from which two examples of some practical interest are derived, i.e., a single absorbing layer on a nonabsorbing substrate and two identical absorbing layers on either side of a nonabsorbing substrate. The solutions are substantially simplified when Faraday‐rotation angles are small.