User-friendly graphic user interface software named IAST++, which was developed, can fit the adsorption data to various isotherm models and use the ideal adsorbed solution theory (IAST) to obtain mixture isotherm data. In the Modeler module of the IAST++, automatic model suggestion functionality exists, and users can readily visualize the fitting data via the built-in visualization module. In the IAST module of the IAST++, users can import an arbitrary number of pure isotherm data and have the option of selecting desired system variables (e.g., system pressure and gas composition or total uptake and adsorbed phase composition) to obtain the mixture isotherm data. The results of the IAST calculations are shown in both raw data form and visualization module, making IAST++ attractive software for both experimental and computational researchers.