(a) On a loan contract that includes precomputed interest or uses the scheduled installment earnings method and that is a regular transaction, an authorized lender may charge additional interest for the deferment of an installment if:
(1) the entire amount of the installment is unpaid;
(2) no interest for default has been collected on the installment; and
(3) payment of the installment is deferred for one or more full months and the maturity of the contract is extended for a corresponding period.
(b) The interest for deferment under Subsection (a) may not exceed the amount computed by:
(1) taking the difference between the refund that would be required for prepayment in full as of the date of deferment and the refund that would be required for prepayment in full one month before the date of deferment; and
(2) multiplying the results under Subdivision (1) by the number of months in the deferment period.

(c) The amount of interest applicable to each deferred balance or installment period occurring after a deferment period remains the amount applicable to that balance or period under the original loan contract.
(d) If a loan is prepaid in full during the deferment period, the borrower shall receive, in addition to the refund required under Subchapter H, a pro rata refund of that part of the interest for deferment applicable to the number of full months remaining in the deferment period on the payment date.
(e) For the purposes of this section, a deferment period is the period during which a payment is not required or made because of the deferment and begins on the day after the due date of the scheduled installment that precedes the first installment being deferred.