(a) A secondary mortgage loan that is a regular transaction may provide for an interest charge on the cash advance that is precomputed and that does not exceed a rate or amount that would produce the same effective return as allowed under Subchapter A, Chapter 303.
(b) For the purpose of Subsection (a):
(1) when the loan is made an interest charge may be computed for the full term of the loan contract;
(2) if the period before the first installment due date includes a part of a month that is longer than 15 days, that portion of a month may be considered a full month; and
(3) if a loan contract provides for precomputed interest, the amount of the loan is the total of:
(A) the cash advance; and
(B) the amount of precomputed interest.

(c) A secondary mortgage loan may provide for a rate or amount of interest calculated using the true daily earnings method or the scheduled installment earnings method that does not exceed the alternative rate ceiling in Subchapter A, Chapter 303. Interest may accrue on the principal balance and amounts added to principal after the date of the loan contract from time to time unpaid at the rate provided for by the contract until the date of payment in full or demand for payment in full. An interest charge under this subsection may not be precomputed.