Section 1141.1 - Procedures to calculate interest rates(a) For purposes of complying with a Board decision in an investigation or complaint proceeding, interest rates to be computed shall be the most recent U.S. Prime Rate as published by The Wall Street Journal. The rate levels will be determined as follows:(1) For investigation proceedings, the interest rate shall be the U.S. Prime Rate as published by The Wall Street Journal in effect on the date the statement is filed accounting for all amounts received under the new rates.(2) For complaint proceedings, the interest rate shall be the U.S. Prime Rate as published by The Wall Street Journal in effect on the day when the unlawful charge is paid. The interest rate in complaint proceedings shall be updated whenever The Wall Street Journal publishes a change to its reported U.S. Prime Rate. Updating will continue until the required reparation payments are made.(b) For investigation proceedings, the reparations period shall begin on the date the investigation is started. For complaint proceedings, the reparations period shall begin on the date the unlawful charge is paid.(c) For both investigation and complaint proceedings, the annual percentage rate shall be the same as the annual nominal (or stated) rate. Thus, the nominal rate must be factored exponentially to the power representing the portion of the year covered by the interest rate. A simple multiplication of the nominal rate by the portion of the year covered by the interest rate would not be appropriate because it would result in an effective rate in excess of the nominal rate. Under this "exponential" approach, the total cumulative reparations payment (including interest) is calculated by multiplying the interest factor for each period by the principal amount for that period plus any accumulated interest from previous periods. The "interest factor" for each period is 1.0 plus the interest rate for that period to the power representing the portion of the year covered by the interest rate. 78 FR 44460 , July 24, 2013