Tex. Finance Code § 353.107: CHARGE FOR DEFAULT IN PAYMENT OF INSTALLMENT.

(a) A retail installment contract may provide that if an installment remains unpaid after the 10th day after the maturity of the installment for a heavy commercial vehicle or after the 15th day after the maturity of the installment for any other commercial vehicle the holder may collect:

(1) a delinquency charge that does not exceed five percent of the amount of the installment; or

(2) interest on the amount of the installment accruing after the maturity of the installment and until the installment is paid in full at a rate that does not exceed the maximum rate authorized for the contract.

(b) A retail installment contract that provides for the true daily earnings method or the scheduled installment earnings method may provide for the delinquency charge authorized by Subsection (a)(1), the interest authorized by Subsection (a)(2), or both.

(c) Only one delinquency charge under Subsection (a)(1) may be collected on an installment under this section regardless of the duration of the default.

Added by Acts 2011, 82nd Leg., R.S., Ch. 117 (H.B. 2559), Sec. 17, eff. September 1, 2011.