Solvent effects on protonation equilibria of various aliphatic, alicyclic, and aromatic amines were estimated by means of a self-consistent isodensity-polarized electrostatic continuum model in combination with the B3LYP/6-31G* and B3LYP/aug-cc-pVDZ//B3LYP/6-31G* calculation schemes. Our results suggest that the found relationship between calculated relative and experimental basicities in water can be used for interpolation or extrapolation in order to calculate pK a values of organic bases with variable structural properties. The found standard deviation of calculated pK a values amounts to 0.7 pK a units. In this paper, we note successful use of this strategy as well as its limits.