The Certificate of Deposit Index (CODI) is the 12 month average of the monthly average yields on the nationally published 3-Month Certificate of Deposit rates. Lenders calculate the average by adding the 12 most recently published monthly yields published by the Federal Reserve together and dividing the result by 12.

Because this index is an annual average, it is more steady than CMT and CD indexes which are very volatile and generally considered to react quickly to change in the market. The CODI and MTA indices generally fluctuate slightly more than the 11th District COFI, although their movements track each other very closely, the MTA, COFI and CODI-indexed ARMs work much the same way. Also available are the Libor and Prime Rate indexes.