An analytical procedure is presented which enables a fast estimate of collision energy dependent cross-section effects on thermal charge exchange spectra. The model is based both on experimental evidence and also on numerical simulations showing that the observed ex spectra are essentially Gaussian in their shape. The collision energy dependent emission rate leads effectively to a line-shift (apparent velocity), usually to a reduction in line-width (apparent temperature), and also to a change in the effective emission rate averaged over the entire thermal velocity distribution function. The cross-section effect is described by an operator which retains the characteristics of a Maxwellian velocity distribution function, and which can be approximated by an exponential expression with only linear and quadratic velocity dependent terms in its exponent. This is the equivalent of a Taylor expansion of the emission rate expressed by its local value Q0(vcol) = eff (vcol)vcol, its gradient dQ/dvcol and its curvature d2Q/dv2col. As a result of this approximation, the integration in velocity space, which is required for the calculation of the observed spectral shape, is reduced to an algebraic expression. The predictions of the model are compared to full numerical calculations which solve a 3- dimensional integral in velocity space. It is shown, that the analytical model is applicable up to thermal velocities approximately one third of the beam velocity. This limit corresponds to ion temperatures below 40keV for the CVI spectrum, and ion temperatures below 10keV for the Hell (atomic mass units 3). Beyond this limit significant deviations from a Gaussian- like spectrum must be expected. A deconvolution procedure is described, which enables the reconstruction of true temperature, velocity and intensities from measured CX spectra, using the algebraic expressions for the cross-section effects. Examples taken from the previous JET experimental campaign are used to illustrate the cross-section effects on low-Z impurity CX spectra for a comprehensive variety of neutral beams (deuterium, tritium or helium), target densities, temperatures and toroidal rotation speeds. An overview is given of representative correction factors established for high-power, high-temperature plasmas, as well as for plasmas with combined neutral beam and radio frequency heating, and also for the case of locked modes where CX velocity corrections play a role in the assessment of toroidal velocities close to zero.