An index used to establish interest rates for adjustable rate mortgages. It is based on the yields of actively traded 1-year, 3-year, or 5-year Treasury Securities adjusted to constant maturities. The Treasury Security indices are calculated by the U.S. Treasury and reported by the Federal Reserve Board. These indices have either a weekly or a monthly value. The weekly indices are released on Monday afternoon for the previous week. Monthly values for these indices are generally available on the first Monday of the following month.