Missouri late fee law

9%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.

Creditors are allowed interest at 9% per annum, when no other rate is agreed upon, for all moneys after they become due and payable on written contracts, and on accounts after they become due and demand of payment is made. Verified on the official Missouri Revisor of Statutes site. Note: on open accounts, interest runs from demand for payment.

Broad freedom for B2B credit: under § 408.035 (verified on revisor.mo.gov) parties may agree in writing to ANY rate of interest, fees and terms for (1) loans to corporations, general or limited partnerships, or LLCs; (2) extensions of credit primarily for agricultural, business or commercial purposes; (3) non-residential real estate loans; or (4) loans of $5,000+ secured by listed financial instruments. For credit not within these exemptions, § 408.030 caps the contract rate (market rate per published index or 10%) - most commercial/trade credit falls inside the § 408.035 exemptions.

public+private-construction

Public construction: § 34.057 (Missouri Prompt Payment Act) - owner must pay prime within 30 days of invoice; prime must pay subs within 15 days of receipt; late payments withheld in bad faith can bear a penalty of 1.5% per month (Missouri appellate courts hold this is simple interest). Private construction: § 431.180 - payments due per the contract; an unpaid party may sue and the court may award interest at up to 18% per annum plus reasonable attorney fees (rate per corroborated secondary sources). No general prompt-payment statute for ordinary private non-construction B2B invoices was found (they fall back on § 408.020's 9% after demand).

Because § 408.035 exempts business-purpose credit from usury limits, agreed late charges on B2B invoices are principally tested under the liquidated-damages/penalty doctrine (reasonable forecast of harm) rather than usury. Absent an agreed charge, the remedy is 9% interest from demand under § 408.020.