A Microsoft Visual Basic program, WinTcac, has been developed to calculate structural formulae of tourmaline analyses based on the Subcommittee on Tourmaline Nomenclature (STN) of the International Mineralogical Association's Commission on New Minerals, Nomenclature and Classification (IMA-CNMCN) scheme. WinTcac calculates and classifies tourmaline-supergroup minerals based on 31 O atoms for complete tourmaline analyses. For electron-microprobe-derived tourmaline analyses site occupancy can be estimated by using the stoichiometric H2O (wt%) and B2O3 (wt%) contents. This program also allows the user to process tourmaline analyses using 15 cations and 6 silicons normalization schemes. WinTcac provides the user to display tourmaline analyses in a various classification, environmental, substitution, and miscellaneous plots by using the Golden Software's Grapher program. The program is developed to predict cation site-allocations at the different structural positions, including the T, Z, Y, and X sites, as well as to estimate the OH1-, F1-, Cl1-, and O2- contents. WinTcac provides editing and loading Microsoft Excel files to calculate multiple tourmaline analyses. This software generates and stores all the calculated results in the output of Microsoft Excel file, which can be displayed and processed by any other software for verification, general data manipulation, and graphing purposes. The compiled program code is distributed as a self-extracting setup file, including a help file, test data files and graphic files, which are designed to produce a high-quality printout of the related plotting software. © 2013 Elsevier Ltd.