The Federal Cost of Funds Index (Fed COFI) is used as a benchmark for some types of mortgage loans and securities. It is calculated as the sum of the monthly average interest rates for marketable Treasury bills and for marketable Treasury notes, divided by two, and rounded to three decimal places.
Freddie Mac doesn't define exactly which "marketable Treasury bills and marketable Treasury notes" are included in its calculations, or whether or not they follow a calendar month, utilize weighted averages or other information.
The Federal COFI is made available by Freddie Mac on or about the 20th day of each month. Freddie Mac first began publicly providing the Federal COFI in March, 1991; values are calculated for earlier years to illustrate what the index values would have been for those periods and are provided for research purposes only. The Federal COFI is not adjusted to reflect subsequent changes in the underlying Treasury rates once the value has been posted.
According to the Office of the Comptoller of the Currency (OCC), the Federal Cost of Funds can be used as a replacement for the discontinued Monthly Median Annualized Cost of Funds formerly published by the Office of Thrift Supervision (OTS).