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Interest on unpaid invoices in Missouri: 9% a year if no rate was agreed; the most you can set depends on the deal

By Yossi Grunwald, founder of Workeey · Updated

In Missouri, 9% a year if no rate was agreed; the most you can set depends on the deal. Read from Missouri's own statutes, agencies and courts, checked November 6, 2026, with every answer quoted below, and a late fee calculator.

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Missouri's rate when no rate was agreed

9% a year. RSMo 408.020: 9% a year when no other rate is agreed — on written contracts once due, and on accounts once due AND payment has been demanded.

  • “Creditors shall be allowed to receive interest at the rate of nine percent 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” — RSMo 408.020, read November 6, 2026

The most you can set in Missouri

For a homeowner: It depends: see RSMo 408.030. Up to 10% a year agreed in writing on money due under any contract, or the quarterly 'market rate' (long-term U.S. government bond index + 3 points) when that is higher; consumer loans under RSMo 408.100 at rates agreed by the parties.

For a business customer: Any rate agreed in writing for an extension of credit primarily for business or commercial purposes, or a loan to a corporation, partnership or LLC.

How the most you can set moves: Max written rate: higher of 10% or the quarterly market rate = long-term U.S. government bond index (second month before the quarter) + 3 points, posted by the Division of Finance (RSMo 408.030.3).

  • “Parties may agree, in writing, to a rate of interest not exceeding ten percent per annum on money due or to become due upon any contract, including a contract for commitment; except that, when the "market rate" exceeds ten percent per annum, parties may agree, in writing, to a rate of interest not exceeding the "market rate".” — RSMo 408.030.1, read November 6, 2026
  • “The "market rate" for any calendar quarter shall be equal to the monthly index of long term United States government bond yields for the second preceding calendar month prior to the beginning of the calendar quarter plus an additional three percentage points rounded off to the nearest tenth of one percent.” — RSMo 408.030.3, read November 6, 2026
  • “This section shall apply to all loans which are not made as permitted by other laws of this state except that it shall not apply to loans which are secured by a lien on real estate.” — RSMo 408.100, read November 6, 2026
  • “Notwithstanding the provisions of any other law to the contrary, it is lawful for the parties to agree in writing to any rate of interest, fees, and other terms and conditions in connection with any: (1) Loan to a corporation, general partnership, limited partnership or limited liability company; (2) Extension of credit primarily for agricultural, business, or commercial purposes;” — RSMo 408.035, read November 6, 2026

Late fees in Missouri

It depends: see RSMo 408.140.1(3). Extensions of credit governed by RSMo 408.100 (loans not made under other Missouri laws, not secured by real estate). It depends: see RSMo 408.140 and 408.100.

  • “If the contract so provides, a charge for late payment on each installment or minimum payment in default for a period of not less than fifteen days in an amount not to exceed five percent of each installment due or the minimum payment due or fifteen dollars, whichever is greater, not to exceed fifty dollars.” — RSMo 408.140.1(3), read November 6, 2026
  • “No further or other charge or amount whatsoever shall be directly or indirectly charged, contracted for or received for interest, service charges or other fees as an incident to any such extension of credit except as provided and regulated by sections 367.100 to 367.200 and except:” — RSMo 408.140.1, read November 6, 2026

Does Missouri want it agreed in advance?

Agreed in advance: yes, in the cases below. The consumer late charge only 'if the contract so provides' (408.140). Without an agreed rate, 9% runs on an account only after it is due and payment has been demanded (408.020).

  • “Parties may agree, in writing, to a rate of interest not exceeding ten percent per annum” — RSMo 408.030.1, read November 6, 2026
  • “If the contract so provides, a charge for late payment” — RSMo 408.140.1(3), read November 6, 2026

Homeowners and businesses in Missouri

Homeowner: 10% (or market rate) written cap and, for consumer credit, the 408.140 late-charge limits; owner-occupied homes of 4 units or less are outside the prompt-pay statute. Business customer: any written rate (408.035). See RSMo 408.030, 408.035, 408.140, 431.180.3.

  • “Extension of credit primarily for agricultural, business, or commercial purposes;” — RSMo 408.035(2), read November 6, 2026

Prompt payment on private construction in Missouri

What the text says: Court may award interest of up to 1.5% per month from the date payment was due under the contract, plus attorney fees to the prevailing party. Contracts for private design or construction work (including repair); does NOT apply to building, improvement, repair or remodeling of owner-occupied residential property of four units or less. RSMo 431.180.

  • “interest at the rate of up to one and one-half percent per month from the date payment was due pursuant to the terms of the contract, and reasonable attorney fees, to the prevailing party.” — RSMo 431.180.2, read November 6, 2026
  • “The provisions of this section shall not apply to contracts for private construction work for the building, improvement, repair or remodeling of owner-occupied residential property of four units or less.” — RSMo 431.180.3, read November 6, 2026

Work out a late charge in Missouri

Starts at Missouri's 9%, the rate when none was agreed, not a maximum.

Days since the due date
The rate or fee your terms set

$8.88 late charge

Days late
30
New total
$1,208.88

$1,200.00 × 9% a year × 30 days ÷ 365 = $8.88

What was not checked for Missouri

  • Missouri's current quarterly "market rate" was not found on the Division of Finance site.
  • Missouri's retail charge and retail installment sale laws (chapter 365) were not read.

Check Missouri's own text

Before you charge: read RSMo 408.020 and the other Missouri texts quoted on this page, or ask a lawyer. As of November 6, 2026.

This is a plain-words summary of each state's own laws as of November 6, 2026, not legal advice. Rules have exceptions. Check the state's own text, linked on every state's page, or a lawyer before you charge a late fee or interest.

Compare Missouri with every state's answer, or with its neighbours just below.

Next door to Missouri

  • Arkansas: depends if none agreed, 17% by agreement (not fully confirmed)
  • Illinois: 5% if none agreed, 9% for homes
  • Iowa: 5% if none agreed, depends by agreement
  • Kansas: 10% if none agreed, depends by agreement
  • Kentucky: 8% if none agreed, depends by agreement
  • Nebraska: 12% if none agreed, 16% for homes (two answers)
  • Oklahoma: 6% if none agreed, depends by agreement
  • Tennessee: up to 10% if none agreed (not fully confirmed)

Official sources for Missouri

Every state in one file: Excel and CSV downloads

Where our data comes from

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