Stacked complexes made of phenol and substituted benzenes are studied via MP2 calculations in order to investigate the influence of the stacking interaction on the acidity of phenol. Aqueous-phase proton affinities have been computed and converted to pK a values using a calibration procedure involving a set of substituted phenols. Both T-shaped and parallel-displaced conformations lead to an appreciable decrease in the pK a , with the largest effect found for T-shaped arrangements. Local and global DFT based reactivity descriptors are used to analyze the effect of the stacking partner as well as the interaction between the aromatic rings.