Definition: The mortgage default rate (MFR) refers to the annualized rate at which a borrower defaults on their home loan payments by failing to make timely and sufficient monthly principal and interest payments for 30 days. The MFR can be calculated using a formula that calculates the percentage of outstanding loans based on a range of values from 2% up to 15%. The mortgage default rate is typically reported as an annual percentage point (APY) or a percent change in value, depending on the reporting standard for the MFR. It's an important indicator for borrowers who may be facing financial hardships due to their inability to pay their mortgages on time and they may need to seek assistance from various government agencies. In summary, mortgage default rate refers to the annualized percentage point of a borrower's loan that defaults.