The Federal Home Loan Bank of San Francisco said the monthly weighted average cost of funds for the 11th district was 4.904% in August, up from 4.887% in July.
The cost of funds index, or Cofi, is the benchmark against which many adjustable rate mortgages are set. It is based on the interest paid by savings institutions in Arizona, California, and Nevada to fund their mortgage products.
Traders at eight firms surveyed by Bloomberg News had expected a rate of 4.892%.
The Federal Home Loan Bank announces the rate at 3 p.m. the final business day of each month.