32 C.F.R. § 34.42
(b) Financial records, supporting documents, statistical records, and all other records pertinent to an award shall be retained for a period of three years from the date of submission of the final expenditure report. The only exceptions are the following:
(g) Indirect cost proposals, cost allocation plans, and other cost accounting documents (such as documents related to computer usage chargeback rates), along with their supporting records, shall be retained for a 3-year period, as follows: