IFRS 9 credit risk modelling is one of the most misunderstood areas in banking.Most professionals understand the theory : PD, LGD, EAD, staging, ECL  but struggle when it comes to practical implementation:• PIT vs TTC calibration• Lifetime PD construction• Macroeconomic overlays• Model governance and validationThis article explains how IFRS 9 credit risk models are built and used in real banks,based on hands-on implementation experience across SAS, Python, and Excel.