Interest on unpaid invoices in Wisconsin: 5% a year if no rate was agreed; the most you can set depends on the deal

Wisconsin's rate when no rate was agreed

5% a year. 5% a year on the loan or forbearance of money, goods or things in action; any higher contract rate allowed by other sections must be 'clearly expressed in writing'. (Official annotation: interest on a liquidated claim runs from when payment was due under the contract, or if no time is set, from demand or suit.)

• “The rate of interest upon the loan or forbearance of any money, goods or things in action shall be $5 upon the $100 for one year and according to that rate for a greater or less sum or for a longer or a shorter time; but parties may contract for the payment and receipt of a rate of interest not exceeding the rate allowed in ss. 138.041 to 138.056 , 138.09 to 138.14 , 218.0101 to 218.0163 , or 422.201 , in which case such rate shall be clearly expressed in writing.” — Wis. Stat. § 138.04, read November 6, 2026
• “A creditor is entitled to interest on a liquidated claim from the time payment was due by the terms of the contract and, if no time is specified, then from the time demand was made or from commencement of the action.” — Wis. Stat. § 138.04, annotation (Estreen v. Bluhm), read November 6, 2026

The most you can set in Wisconsin

For a homeowner: No maximum for consumer credit transactions under the Wisconsin Consumer Act entered into after Oct 31, 1984 (finance charge must be agreed). § 138.05 does not apply to transactions governed by chs. 421–427 (the Wisconsin Consumer Act) — a consumer credit transaction is credit to a non-organization customer for personal, family or household purposes, payable in installments or with a finance charge. It depends: see Wis. Stat. §§ 138.04, 138.05, 422.201.

For a business customer: The cap does not apply to loans to corporations or LLCs, or to loans/forbearances of $150,000 or more (unless secured by the borrower's 1–4 family home). Wis. Stat. § 138.05(5), (7). It depends: see § 138.05.

• “(bn) A consumer credit transaction entered into after October 31, 1984, is not subject to any maximum limit on finance charges.” — Wis. Stat. § 422.201(2)(bn), read November 6, 2026
• “Except as authorized by other statutes, no person shall, directly or indirectly, contract for, take or receive in money, goods or things in action, or in any other way, any greater sum or any greater value, for the loan or forbearance of money, goods or things in action, than: 138.05(1)(a) (a) At the rate of $12 upon $100 for one year computed upon the declining principal balance of the loan or forbearance;” — Wis. Stat. § 138.05(1)(a), read November 6, 2026
• “(5) This section shall not apply to loans to corporations or limited liability companies. 138.05(6) (6) This section does not apply to transactions governed by chs. 421 to 427 and 429 or to discounts described in s. 422.201 (8) .” — Wis. Stat. § 138.05(5)-(6), read November 6, 2026
• “"Consumer credit transaction" means a consumer transaction between a merchant and a customer in which real or personal property, services or money is acquired on credit and the customer’s obligation is payable in installments or for which credit a finance charge is or may be imposed” — Wis. Stat. § 421.301(10), read November 6, 2026
• “"Customer" means a person other than an organization (s. 421.301 (28) ) who seeks or acquires real or personal property, services, money or credit for personal, family or household purposes” — Wis. Stat. § 421.301(17), read November 6, 2026
• “(7) This section does not apply to any loan or forbearance in the amount of $150,000 or more made after May 26, 1978 unless secured by an encumbrance on a one- to four-family dwelling which the borrower uses as his or her principal place of residence.” — Wis. Stat. § 138.05(7), read November 6, 2026

Late fees in Wisconsin

What the text says: Consumer credit transactions (not open-end): if agreed, a delinquency charge of the lesser of $10 or 5% of the unpaid installment, only on an installment not paid in full by the 10th day after due, collected once per installment. Consumer credit transactions other than open-end credit plans (Wisconsin Consumer Act, chs. 421–427).

• “With respect to a consumer credit transaction other than one pursuant to an open-end credit plan, the parties may agree to a delinquency charge on any installment not paid in full on or before the 10th day after its scheduled or deferred due date in an amount not to exceed $10 or 5 percent of the unpaid amount of the installment, whichever is less.” — Wis. Stat. § 422.203(1), read November 6, 2026
• “A delinquency charge under sub. (1) may be collected only once on an installment however long it remains in default.” — Wis. Stat. § 422.203(3), read November 6, 2026
• “"Consumer credit transaction" means a consumer transaction between a merchant and a customer in which real or personal property, services or money is acquired on credit and the customer’s obligation is payable in installments or for which credit a finance charge is or may be imposed” — Wis. Stat. § 421.301(10), read November 6, 2026

Does Wisconsin want it agreed in advance?

Agreed in advance: yes, in the cases below. A rate above 5% must be 'clearly expressed in writing' (§ 138.04); the consumer delinquency charge requires that 'the parties may agree' to it (§ 422.203). Official annotation: a merchant who first disclosed 24% interest on an open account only in statements sent after the account was opened was entitled only to the § 138.04 legal rate.

• “The rate of interest upon the loan or forbearance of any money, goods or things in action shall be $5 upon the $100 for one year and according to that rate for a greater or less sum or for a longer or a shorter time; but parties may contract for the payment and receipt of a rate of interest not exceeding the rate allowed in ss. 138.041 to 138.056 , 138.09 to 138.14 , 218.0101 to 218.0163 , or 422.201 , in which case such rate shall be clearly expressed in writing.” — Wis. Stat. § 138.04, read November 6, 2026
• “With respect to a consumer credit transaction other than one pursuant to an open-end credit plan, the parties may agree to a delinquency charge on any installment not paid in full on or before the 10th day after its scheduled or deferred due date in an amount not to exceed $10 or 5 percent of the unpaid amount of the installment, whichever is less.” — Wis. Stat. § 422.203(1), read November 6, 2026
• “A merchant who first informed the customer of the 24 percent interest to be charged on an open account in statements of the account provided after the account was opened violated s. 422.302 (2). The merchant was only entitled to interest under this section.” — Wis. Stat. § 138.04, annotation (Severson Agri-Service, Inc. v. Lander, published with the official annotated statutes), read November 6, 2026

Homeowners and businesses in Wisconsin

For a consumer (non-organization customer, personal/family/household purpose) on credit, the Wisconsin Consumer Act governs: no finance-charge ceiling after 1984 but a $10/5% delinquency-charge cap. Wis. Stat. § 138.05 does not apply to loans to corporations or limited liability companies.

• “"Customer" means a person other than an organization (s. 421.301 (28) ) who seeks or acquires real or personal property, services, money or credit for personal, family or household purposes” — Wis. Stat. § 421.301(17), read November 6, 2026
• “(bn) A consumer credit transaction entered into after October 31, 1984, is not subject to any maximum limit on finance charges.” — Wis. Stat. § 422.201(2)(bn), read November 6, 2026
• “With respect to a consumer credit transaction other than one pursuant to an open-end credit plan, the parties may agree to a delinquency charge on any installment not paid in full on or before the 10th day after its scheduled or deferred due date in an amount not to exceed $10 or 5 percent of the unpaid amount of the installment, whichever is less.” — Wis. Stat. § 422.203(1), read November 6, 2026
• “(5) This section shall not apply to loans to corporations or limited liability companies. 138.05(6) (6) This section does not apply to transactions governed by chs. 421 to 427 and 429 or to discounts described in s. 422.201 (8) .” — Wis. Stat. § 138.05(5)-(6), read November 6, 2026

Prompt payment on private construction in Wisconsin

Not found in our check for Wisconsin.

Work out a late charge in Wisconsin

Starts at Wisconsin's 5%, the rate when none was agreed, not a maximum.

What was not checked for Wisconsin

• Wisconsin was not searched to the end for a prompt-payment law on private construction.

Check Wisconsin's own text

Before you charge: read Wis. Stat. § 138.04 and the other Wisconsin 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 Wisconsin with every state's answer, or with its neighbours just below.

Next door to Wisconsin

• Illinois: 5% if none agreed, 9% for homes
• Iowa: 5% if none agreed, depends by agreement
• Michigan: 5% if none agreed, depends by agreement
• Minnesota: 6% if none agreed, depends by agreement

Official sources for Wisconsin

• Wis. Stat. § 138.04 — read November 6, 2026
• Wis. Stat. § 422.201(2)(bn) — read November 6, 2026
• Wis. Stat. § 138.05(1)(a) — read November 6, 2026
• Wis. Stat. § 421.301(10) — read November 6, 2026
• Wis. Stat. § 422.203(1) — read November 6, 2026

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