TPgui is a graphical user interface and calibration tool for the thermoplastic (TP) model for polymers. TPgui attempts to calculate model parameters that minimize the difference between experimental stress-strain data and the stress-strain curve predicted by the TP model. TPgui is built entirely using MATLAB and runs on Linux or Windows workstations or laptops. TPgui exploits the multi-processing capabilities of the computational environment, if available, during parameter optimization.