Evaporation time and solvent balance are important properties of solvent blends used in coatings systems. Linear mixing rules allow accurate calculation of many solution properties for solvent blends; however, such rules cannot be applied to the determination of evaporation time and solvent balance since these properties are particularly sensitive to non-ideal behavior in mixtures. A mathematical model of solvent blend evaporation is proposed which accounts for mixture non-idealities in terms of component activity coefficients. The model allows accurate prediction of blend evaporation time, and solvent composition during evaporation may be followed. The model has been incorporated into a general computer program for calculation of solvent blend properties. -- AATA