The visible tunable filter is an imaging spectropolarimeter for solar observations in visible light. The instrument consists of several Fabry–Pérot interferometers (FPIs), a polarization modulator, and a prefilter. It will be one of the first light instruments for the Daniel K. Inouye Solar Telescope (DKIST) on Haleakaláa, Maui, Hawaii. We have developed simulation algorithms to describe the instrument and its impact on scientific observations. Our aim is to study the expected measurement accuracy and to test calibration algorithms. A well-known problem is the surface quality of the glass plates for each FPI. We developed algorithms to describe the influence of a surface microroughness, reflectivity, and figure errors of the individual FPI plates, and the expected total photon flux for scientific data acquisition. This tool is used to derive the limits for manufacturing processes to achieve the measurement accuracy required for science observations with DKIST.