The mortgage market has experienced significant shifts over the past few decades, driven by changing economic conditions, market dynamics, and regulatory responses. One key area of focus has been mortgage default rates, which serve as a crucial indicator of the health and stability of the housing market. Fannie Mae’s mortgage default rates, spanning from 1999 to 2023, offer a valuable lens through which we can examine these changes. This analysis explores how lending practices, borrower characteristics, and macroeconomic factors have evolved, particularly during two critical periods: the 2007-2009 financial crisis and the post-crisis period in 2019. By examining key factors such as credit scores, loan-to-value (LTV) ratios, debt-to-income (DTI) ratios, and first-time home buyer trends, we can gain insights into the underlying drivers of mortgage default rates and the effectiveness of policy reforms aimed at improving market stability.