Texas late fee law

6%per year

Attaches to the debt by operation of law when you agreed no rate, so it accrues before any lawsuit and can be stated on a demand letter.

When a creditor has not agreed with the obligor to charge any interest, the creditor may charge legal interest at 6% per year on the principal, beginning on the 30th day after the date the amount is due. Statute text verified on two independent statute mirrors (texas.public.law and FindLaw); the official statutes.capitol.texas.gov site could not be fetched programmatically.

Parties may contract for interest; usury ceilings come from Tex. Fin. Code ch. 303's optional rate ceilings, which float with market rates but have an 18% floor and a 24% cap for most contracts, raised to 28% for contracts made for a business, commercial, investment, or similar purpose (§ 303.009). Fin. Code ch. 306 separately governs commercial loans (including special rules for qualified commercial loans); details of ch. 306 not independently verified here - verify with counsel.

public+private-construction

Government: Tex. Gov't Code ch. 2251 (Prompt Payment Act) - overdue payments by governmental entities accrue interest from the day they become overdue at 1% plus the Wall Street Journal prime rate published the first business day of the preceding July (§ 2251.025); payment is generally due in 30 days. Private construction: Tex. Prop. Code ch. 28 - unpaid amounts bear interest at 1.5% per month, accruing the day after payment is due (§ 28.004).

Agreed flat late fees on commercial invoices are generally enforceable if reasonable, subject to the liquidated-damages/penalty doctrine. Because Texas defines interest broadly and enforces usury ceilings with significant penalties (Fin. Code chs. 302-305), late charges that function as compensation for the use or forbearance of money can be scrutinized as interest for usury purposes - structure charges carefully and verify with counsel; this recharacterization risk was not independently researched here.