This paper presents a study aimed at validating the ability of the presently available models to predict the Cotton–Mouton (C–M) effect. The Faraday rotation and the C–M phase shift angle can be calculated by means of a rigorous numerical solution of Stokes equations. Numerical and approximated solutions are presented and compared with experimental data. A detailed comparison is done with the time traces of measurements, inside a limited dataset representative of JET regimes. A statistical analysis is then carried out on a dataset including data from 300 discharges. In general the C–M measurements are in agreement with the numerical model, and the line integral of plasma density deduced by the C–M measurements is in agreement with that measured by LIDAR Thomson scattering (well inside the experimental error, which is close to two fringes for the polarimetry measurements, 1 fringe = 1.14 × 1019 m−2).