Montana late fee and interest rules for invoices

Here is what Montana law says about late fees and interest on unpaid invoices, for business clients and consumers, with the statute and a link to the official source.

This is general information, not legal advice. Laws change and can apply differently to your situation, so check your state's current law or ask a lawyer before you charge a late fee, interest or a deposit. Last reviewed October 21, 2026.

Montana late fee and interest limits

Rule	Montana
Business-to-business late fee or interest cap	An agreed written rate may not exceed the greater of 15% a year or 6 points above the prime rate.
Consumer cap	No specific limit found for invoices to individuals. Keep the fee reasonable and agreed in writing.
Legal interest rate when no rate was agreed	10% a year once money is due. Judgments carry the prime rate plus 3%.
Statute	Mont. Code Ann. §§ 31-1-106, 31-1-107, 25-9-205
Last reviewed	October 21, 2026

Late fee wording to copy

Agree on the fee before the work starts and show it on every invoice.

Payment is due within 30 days of the invoice date. Balances unpaid after the due date are charged interest of [rate]% per month.
A late fee of $[amount] applies to any balance not paid by the due date.
Past due balances accrue interest at [rate]% per year, or the highest rate allowed by law, whichever is lower.

Keep going

Late fee calculatorWork out the fee or interest on an overdue invoice.How to charge late feesHow to set a late fee and put it on your invoices.Late fee laws by stateEvery state in one table.