GRIP (Generic data Reduction for nulling Interferometry Package) reduces nulling data with enhanced statistical self-calibration methods from any nulling interferometric instrument within a single and consistent framework. The toolbox self-calibrates null depth measurements by fitting a model of the instrumental perturbations to histograms of data. The model is generated using a simulator of the instrument built into the package for the main operating nullers or provided by the user. GRIP handles baseline discrimination and spectral dispersion and features several optimizing strategy, including least squares, maximum likelihood, and MCMC with emcee (ascl:1303.002), and works on GPU using the cupy library.