A numerically efficient model for the evaluation of InGaAsP ridge waveguide laser operation at threshold is presented. It includes the treatment of the electrical behaviour of the junction and an `hybrid¿ optical waveguide analysis that approximately takes into account the coupling between TE and TM modes at the ridge interfaces. The adopted optical model is slightly more complex than the effective refractive index method and the electrical model gives an almost analytical solution; this allows the use of optimisation routines in designing structures which present minimum threshold current. Numerical results that highlight the advantages of this method in the optical modal analysis are reported and three widely used laser structures are numerically analysed and compared.