The certificate of deposit index, or CODI index, is an index based on the average interest rates of six-month certificates of deposits, or CDs. The CODI index is used by some lenders in order to extend credit by using adjustable rate loans, but the exact use of the CODI index is specific to the individual lender. The CODI index is based on data compiled by the federal government and shows the interest rates that banks are paying on CDs. This data is based on an average over the past 12 months. This index is usually available to the lending organizations around the first Monday of each month. The CODI index is used to determine adjustable rate mortgages in conjunction with the prime rate, treasury bills and the London Interbank Offered Rate, or LIBOR.