31 CFR 205.19 - How is interest calculated?
(b) The interest rate for all interest liabilities for each Federal assistance program subject to this subpart A is the annualized rate equal to the average equivalent yields of 13-week Treasury Bills auctioned during a State's fiscal year. We provide this rate to each State.
(e) A State may use actual data, a clearance pattern, or statistical sampling to calculate interest. A clearance pattern used to calculate interest must meet the standards of § 205.20. If a State uses statistical sampling to calculate interest, the State must sample transactions separately for each Federal assistance program subject to this subpart A. Each sample must be representative of the pool of transactions and be of sufficient size to accurately represent the flow of Federal funds under the Federal assistance program, including seasonal or other periodic variations.
(f) For the first year in which a Federal assistance program is covered in a Treasury-State agreement, funds transfers that occur prior to the first day of the State's fiscal year must not be included in interest calculations and are not subject to the interest liability provisions of this part.