A methodology for the prediction of chemocapacitor responses due to the sorption of vapor analytes is introduced. The approach developed, is based on experimental evaluation of the swelling ability of polymeric sensing materials due to sorption of analytes, consequent calculation of the dielectric constant of the swollen film on the basis of an appropriate mixing rule, in conjunction with electromagnetic modeling for the InterDigitated Electrode (IDE) capacitors. The polymeric film swelling is measured through optical reflectance measurements while the mixing rule applied is the Clausius-Mossotti that is known to be valid for small volume fractions of sorbed analytes in polymeric films. The methodology was successfully applied in various non-polar polymer-analyte systems at low vapor concentrations.