Minnesota 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.

Interest for any legal indebtedness is at the rate of $6 upon $100 for a year (6% per annum) unless a different rate is contracted for in writing. Verified on the official MN Revisor of Statutes site.

Written contracts may provide up to 8% per annum ($8 on $100) under § 334.01, subd. 1. Major B2B exemptions: § 334.01, subd. 2 exempts contracts of $100,000 or more from the rate limitations entirely; and § 334.022 (verified on revisor.mn.gov) removes ALL limits on rate, points, fees and charges for extensions of credit to an 'organization' (corporation, partnership, LLC, joint venture, cooperative, trust, estate, government entity, association) - i.e., no usury cap on credit extended to business organizations.

public+private-construction

Public: Minn. Stat. § 471.425 (municipalities - applies to purchases of goods and services generally, payment within 35 days) and § 16A.124 (state agencies) impose late-payment interest of 1.5% per month, with a $10 minimum monthly penalty on balances of $100+. Private construction: § 337.10 requires monthly progress payments owner→prime (unless contract says otherwise) and payment down the chain within 10 days of receipt, with unpaid/wrongfully withheld amounts bearing 1.5% per month. No general prompt-payment statute for ordinary private non-construction B2B invoices was found.

Agreed late fees on commercial invoices are generally enforceable subject to the liquidated-damages/penalty doctrine. Caution: on contracts under $100,000 between non-organizations, a late charge that functions as interest can run into the 8% written-contract cap; contracts of $100k+ and any credit to business organizations are exempt (§ 334.01 subd. 2; § 334.022).