Definition: The mortgage market index (MII) is a measure of the price levels of real estate assets in the U.S. residential mortgage market that are expected to be refinanced within one year. Definition: The Mortgage Market Index is a financial index that tracks the prices of real estate assets that are expected to be refinanced within one year, as determined by the average annual price change over a specified period (e.g., three months) for the primary mortgage loan and all subsequent mortgage loans. It measures the potential return on investment that would result from investing in these real estate assets. The MII is used by investors, policymakers, financial analysts, and other stakeholders to evaluate the attractiveness of residential mortgages as a source of income. It serves as a benchmark for assessing the economic health and risk of housing markets and can be used to inform investment decisions related to mortgage-backed securities or other housing-related investments.