For the third month in a row, the Monthly Treasury Average has made a move higher, though it still sits in historically low territory.
MTA is used to determine the degree to which interest rates and payment amounts change on a small share of adjustable-rate mortgages.
In January, the index came in at 0.12750 percent, according to a Mortgage Daily analysis of Federal Reserve Board data..
MTA ascended from a month earlier, when it was computed at 0.12083 percent.
The index has risen each month since October 2014, when it registered a record-low 0.11333 percent.
MTA has retreated compared to January 2014, when it stood at 0.12833 percent.
MTA is determined based on the daily average for the one-year Treasury yield for each of the past 12 months. In January, the daily average was 0.20 percent.
The one-year Treasury yield, a far more widely used ARM index than MTA, tumbled to 0.18 percent at the end of January from 0.25 percent one month prior, according to Treasury Department data.
ARMs accounted for 8.9 percent of all product-and-pricing inquiries in the U.S. Mortgage Market Index report from LoanSifter/Optimal Blue and Mortgage Daily for the week ended Jan. 30.
ARM share fell from 9.4 percent a week earlier and sank from 12.7 percent a year earlier.