This document proposes a methodology for dynamically diffusing stress across a credit rating scale when performing stress tests on credit portfolios. It recognizes that existing stress testing practices often do not accurately reflect portfolio behavior under stress. The proposed approach considers how credit score performance impacts default rates across rating classes under stress conditions. It involves using a beta distribution to model default rates pre-and post-stress, then establishing a relationship between credit score metrics like the Gini index and the level of stress applied to each rating class. The approach is demonstrated on a real SME loan portfolio to show how it can more accurately reflect portfolio risks under stress compared to uniform stress diffusion methods typically used.