(a) A creditor may contract for, charge, and receive from an obligor interest or time price differential.
(b) The maximum rate or amount of interest is 10 percent a year except as otherwise provided by law. A greater rate of interest than 10 percent a year is usurious unless otherwise provided by law. All contracts for usurious interest are contrary to public policy and subject to the appropriate penalty prescribed by Chapter 305.
(c) To determine the interest rate of a loan under this subtitle, all interest at any time contracted for shall be aggregated and amortized using the actuarial method during the stated term of the loan.
(d) In addition to interest authorized by Subsection (b), a loan providing for a rate of interest that is 10 percent a year or less may provide for a delinquency charge on the amount of any payment in default for a period of not less than 10 days in an amount not to exceed the greater of five percent of the amount of the payment or $7.50. The charging of the delinquency charge does not make the loan subject to Chapter 342 or any other provision of Subtitle B.