15 U.S. Code § 1615 - Prohibition on use of “Rule of 78’s” in connection with mortgage refinancings and other consumer loans
(a) Prompt refund of unearned interest required
(1) In general
If a consumer prepays in full the financed amount under any consumer credit transaction, the creditor shall promptly refund any unearned portion of the interest charge to the consumer.
(2) Exception for refund of de minimus 1 amount
No refund shall be required under paragraph (1) with respect to the prepayment of any consumer credit transaction if the total amount of the refund would be less than $1.
(3) Applicability to refinanced transactions and acceleration by the creditor
This subsection shall apply with respect to any prepayment of a consumer credit transaction described in paragraph (1) without regard to the manner or the reason for the prepayment, including—
(A) any prepayment made in connection with the refinancing, consolidation, or restructuring of the transaction; and
(b) Use of “Rule of 78’s” prohibited
For the purpose of calculating any refund of interest required under subsection (a) of this section for any precomputed consumer credit transaction of a term exceeding 61 months which is consummated after September 30, 1993, the creditor shall compute the refund based on a method which is at least as favorable to the consumer as the actuarial method.
(c) Statement of prepayment amount
(1) In general
Before the end of the 5-day period beginning on the date an oral or written request is received by a creditor from a consumer for the disclosure of the amount due on any precomputed consumer credit account, the creditor or assignee shall provide the consumer with a statement of—
(2) Written statement required if request is in writing
If the customer’s request is in writing, the statement under paragraph (1) shall be in writing.
(3) 1 free annual statement
A consumer shall be entitled to obtain 1 statement under paragraph (1) each year without charge.
(4) Additional statements subject to reasonable fees
Any creditor may impose a reasonable fee to cover the cost of providing any statement under paragraph (1) to any consumer in addition to the 1 free annual statement required under paragraph (3) if the amount of the charge for such additional statement is disclosed to the consumer before furnishing such statement.
For the purpose of this section—
(1) Actuarial method
The term “actuarial method” means the method of allocating payments made on a debt between the amount financed and the finance charge pursuant to which a payment is applied first to the accumulated finance charge and any remainder is subtracted from, or any deficiency is added to, the unpaid balance of the amount financed.
(2) Consumer, credit
The terms “consumer” and “creditor” have the meanings given to such terms in section 1602 of this title.
The term “creditor”—
(A) has the meaning given to such term in section 1602 of this title; and
 So in original. Probably should be “de minimis”.