The CMT indexes are volatile and move with the market. They reflect the state of the economy, and respond quickly to economic changes. These indexes react more slowly than the CD index, but more quickly than the COF index or the MTA index (see historical graph below).

1-, 3-, and 5-Year CMT, 1994-2004

1-Year Constant Maturity Treasury index (1 Yr CMT)
This is the most widely used index. Roughly half of all ARMs are based on this index. It's used on ARMs with annual rate adjustments.

It is also referred to as the 1-Year Treasury Bill (1Yr T-Bill) , the 1-Year Treasury Security (1Yr T-Sec), or the 1-Year Treasury Spot index.

3-Year Constant Maturity Treasury index (3 Yr CMT)
This index is less popular than the 1-Year CMT. ARMs based on the 3 Year CMT will adjust every three years (3Year ARMs).

It may be referred to as the 3-Year Treasury Security (3Yr T-Sec) index.

5-Year Constant Maturity Treasury index (5 Yr CMT)
Same as the 3 Year CMT, only ARM loans indexed to the 5 Year CMT will adjust once every five years. [The ARM's adjustment period is usually the same as the security's constant maturity.]