The problem of calculating the valence‐band structure of strained‐layer quantum wells in the effective‐mass approximation is reviewed. Using the spherical approximation and exploiting the simplicity of the infinitely deep well model we show that the in‐plane effective mass is determined by two factors—a splitting contribution which is dominant at large strains, and a quantum confinement contribution. A model for finite‐depth wells is presented which gives analytic expressions for the zone‐center in‐plane mass and associated nonparabolicity factor, and it is applied to the system InxGa1−xAs/GaAs. The model allows the computation of valence‐band structure using no more than a pocket calculator. It is shown to give results in reasonable agreement with experiment.