After edging up in December, the Cost of Funds Index reversed course and fell to a new all-time low.
The index came in at 0.768 percent in January, the Federal Home Bank of San Francisco reported Friday.
COFIÂ broke the record set in November and reached the lowest level ever based on FHLB data back to July 1981.
In December, the 11th District index was 0.784 percent.
A year earlier, COFIÂ came in at 0.962 percent — a record-low at the time.
The index is calculated based on interest expenses at FHLB members based in Arizona, California and Nevada.
In January, average total funds used in the calculation were $32.9 billion.
While COFI is used to determine rate and payment changes on some adjustable-rate mortgages, a far more popular ARMÂ index is the yield on the one-year Treasury note.
Data from the Department of the Treasury indicate that the one-year Treasury yield fell to 0.10 percent as of Jan. 31 from 0.13 percent at the end of 2013.
The one-year Treasury yield closed at 0.12 percent as of Feb. 28.
ARMs accounted for 13.7 percent of all activity in the U.S. Mortgage Market Index from LoanSifter and Mortgage Daily for the week ended Feb. 28.
