Oxygen fugacity (fO2) is a fundamental thermodynamic property governing redox potential in solid Earth systems. Analysis of magmatic fO2 aids our understanding of the valence state and solubility of multivalent elements during magma evolution. Specialized software, Geo‐fO2, was developed for calculating magmatic fO2 on the basis of oxybarometers and thermobarometers for common minerals (amphibole, zircon, and biotite) in intermediate‐silicic magmas. With user‐friendly interfaces, it is easy to input files (.csv or Excel files), output data in Excel files, and plot results as binary diagrams that can be saved as vector graphics and modified using image‐processing software.