The Monthly Treasury Average is a relatively new ARM index. This index is the 12 month average of the monthly average yields of U.S. Treasury securities adjusted to a constant maturity of one year. It is calculated by averaging the previous 12 monthly values of the 1-Year Constant Maturity Treasury (CMT) . Because this index is an annual average, it is more steady than the 1-Year CMT index. The MTA index generally fluctuates slightly more than the 11th District 11th District Cost of Funds Index (COFI) , although its movements track each other very closely. The MTA and COFI-indexed ARMs work much the same way. ARMs tied to the MTA index may have the potential for Neg-Am Loan