The results obtained in an interlaboratory evaluation of theoretical modelling methods for single-mode optical fibres, developed in the framework of the COST 217 project, are presented. Values of transmission parameters computed from four different fibre designs are compared with the experimental values obtained in a previous interlaboratory measurement campaign. The consistency of the results obtained with different calculation methods and the accuracy of theoretical predictions are analysed for every one of the usual characterisation parameters of the fibres. The accuracy of the refractive index profile data appears to be the main factor affecting the agreement between theoretically predicted and measured values of the transmission parameters.