Glucose dehydrogenase (GDH) is frequently used for the reduction of NAD+ and NADP+ in bench- and industrial-scale syntheses because the coenzyme regenerating system GDH is easy to apply, robust and relatively inexpensive. To optimize the application of this long known coenzyme regeneration system we investigated the commonly applied Bacillus GDH and characterized this enzyme by its kinetic features in the presence of substrates and products at pH 6.4 and 8.0. Three substrates/products were found to inhibit GDH considerably: (i) the reaction product glucono-1,5-lactone, (ii) the reduced coenzyme NAD(P)H and (iii) the oxidized coenzyme NAD(P)+. The inhibition of GDH under several process conditions was modeled using the determined kinetic constants. It was found that the GDH regeneration system is strongly inhibited by the usually applied conditions. This study provides the rate equation of the GDH reaction and simulations of this coenzyme regenerating system leading to an improved prediction and, thus, to a faster scale-up and increased efficiency of NAD(P)H-dependent synthetic processes.