Oklahoma 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.

'The legal rate of interest shall be six percent (6%) in the absence of any contract as to the rate of interest, and by contract parties may agree to any rate as may be authorized by law.' Text verified via secondary sources reproducing the statute (official OSCN/legislature sites were unreachable during research).

15 O.S. § 266 expressly allows parties to contract for any rate authorized by law. Rate caps in Oklahoma come mainly from the Uniform Consumer Credit Code (Title 14A), which governs consumer (personal/family/household/agricultural-purpose) credit; non-consumer/B2B credit is not subject to the UCCC consumer rate ceilings and the parties' agreed rate generally controls (see 14A O.S. § 3-605 for non-consumer loans). Verify specific transaction types with counsel.

public

State agencies must pay proper invoices within 45 days of receipt (interest calculated from the 30th day if payment not made by the 45th); late-payment interest is set at an annualized rate based on the average rate for 30-day time deposits of state funds during the last calendar quarter of the preceding fiscal year, as reported by the State Treasurer (e.g., 5.00% for FY2024). No Oklahoma prompt-payment statute was found covering private commercial or private construction invoices.

No Oklahoma statute specifically regulating flat late fees on B2B invoices was found; agreed late fees are generally enforceable subject to liquidated-damages/penalty doctrine (15 O.S. §§ 213–215 govern penalties/liquidated damages generally - verify with counsel).