This loan type has a stable payment factor and an interest rate
that changes during the loan’s life cycle. These changes come
from the 12 Month Treasury Average Index, which based on average
annual yields on U.S. Treasury securities adjusted to a constant
maturity of one year made available by the Federal Reserve. The
average is determined by taking the sum of yields from the past
12 months and dividing by 12. The lender then adds a specified number
on points, called a margin, to the index to establish the actual
ARM interest rate. The margin is always a fixed percentage and is
specified in loan documents.
The MTA index does not change as rapidly as other market interest
rates because it is an average of annual yields. The benefits of
this include: higher yields that are offset by lower yields monthly
throughout the year; an index that is far less volatile than other
pure rate indices; and a buffer against interest rate increases
which take longer to affect the MTA than the do other ARM indices.
Historically, home loans tied to the MTA index have not exhibited
sharp interest-rate increases such as those that occurred in the
late 1980’s. The MTA index also has never increased by more
than 0.26 percent from month to month in more than a decade.