This paper presents the ion optical calculations for the deflection magnets of the JET neutral injection system. The large amount of ion power to be handled (26MW) requires more accurate calculations than before. These include 3D magnetic field computations, raytracing and emittance calculations, the latter applied to a multiple aperture ion beam. The resulting power deposition profiles for the full energy ions (80keV hydrogen, 160keV deuterium) and for the fractional energy ions are reported.