A simple analytical model is presented to describe the variation in the yield of excited hydrogen atoms formed by charge exchange as a function of gas target thickness. The model enables the existence of a maximum in the yield and the size of the maximum to be predicted from a minimum of cross-section information. A prediction can also be made for the amount by which the gas target thickness can be reduced in going from the value required for optimum total atom yield to that required for optimum excited atom yield. Both the ratio m of the yield at the maximum to the yield under thick target conditions and the reduction in target thickness r can be expressed in terms of only two independent variables by neglecting certain small cross-sections. Values for m and r are presented as sets of curves on one diagram.From available cross-section data, values for m between 1.0 and 1.5 are predicted for H2, He, Ne, Ar and Xe gases for energies between 25 and 75 keV. The only experimental values of m available are those for Ne, Na and Mg reported by Il'in et al. For Ne the model predicts a value of m of 1.0 at 25 keV which is in agreement with the experiment. Although values of m up to 10 were observed by Il'in et al. for Na and Mg, there is insufficient cross-section data available as yet for these materials for predictions to be made from the model.