Montana Late Fee Calculator
Work out interest on an overdue B2B invoice under Montana law. The legal default rate — what applies when the contract is silent — is 10%, and the statute is quoted verbatim below. All math runs locally in your browser.
Legal rate after the money becomes due (instruments, accounts stated, settled accounts) when no written rate is fixed.
Late fee breakdown
- Interest owed
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- Daily rate
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- Total (invoice + interest)
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Still unpaid? Generate a formal demand letter — it computes the interest and cites Montana's statute (MCA 31-1-106, 31-1-107) for you.
What Montana law actually says
Parties may agree in writing to the payment of any rate of interest that does not exceed the greater of 15% or an amount that is 6 percentage points per year above the prime rate published by the federal reserve system in its statistical release H.15 [...] dated 3 business days prior to the execution of the agreement.
Quoted verbatim from the linked official source — not our paraphrase. How we source and re-check every row is documented in the data methodology.
Maximum late fee in Montana — written B2B contracts
Hard cap 15% (floor).
Cap = greater of 15% or Fed H.15 prime +6 pts; no broad business exemption (only regulated lenders escape). Prime+6 is below 15% now, so 15%/yr binds ordinary B2B.
Basis: Mont. Code Ann. § 31-1-107. Compare all 51 jurisdictions on the full state table and the cap-regime map.
B2B invoices only — not rent, not consumer debt
Everything on this page is about business-to-business invoices. Residential rent late fees live in Montana's landlord-tenant law and consumer credit has separate, stricter rules — two different bodies of law. The distinction is explained in B2B invoice late fees vs. residential rent.
Use this data
Montana's row — rate, cap, citation, verbatim quote, verification date — is part of our open 51-jurisdiction dataset: CSV · JSON (CC BY 4.0, cite myinvoicetemplate.com). Set late-fee terms on your next invoice with the free invoice generator, or state them clearly using the wording guidance in the payment terms guide.
Montana late fee FAQ
Can I charge late fees on overdue invoices in Montana?
Yes — on business-to-business invoices. If your contract or invoice states a late-fee rate, that rate governs (subject to the cap rules below). If nothing was agreed: 10%. Legal rate after the money becomes due (instruments, accounts stated, settled accounts) when no written rate is fixed. Statute: MCA 31-1-106, 31-1-107, verified 2026-08-19. Consumer and rent debts follow separate laws.
What is the maximum late fee I can charge in Montana?
For a written B2B contract: Greater of 15% or Fed H.15 prime +6 pts (dated 3 business days before signing) — prime +6 is currently below the 15% floor, so 15% governs. Basis: Mont. Code Ann. § 31-1-107. The full cap analysis is in the section above; this covers business-to-business deals only — consumer credit has stricter separate caps.
What interest applies if my contract doesn't mention late fees in Montana?
The statutory default rate of 10%. Legal rate after the money becomes due (instruments, accounts stated, settled accounts) when no written rate is fixed. Statute: MCA 31-1-106, 31-1-107 (verbatim quote on this page, verified 2026-08-19).
Does this cover rent, apartment, or consumer late fees in Montana?
No. This page covers business-to-business invoices only. Residential rent late fees are governed by Montana's landlord-tenant law, and consumer credit for personal, family, or household purposes has its own stricter caps and disclosure rules. Those are different statutes than the commercial-interest law cited here.
Where does this data come from, and when was it verified?
Every figure on this page comes from our 51-jurisdiction dataset: each row researched against the controlling statute or the state's official current-rate page, independently re-checked, and stamped with its own verification date — Montana's row was last verified 2026-08-19. The operative legal text is quoted verbatim on this page with a link to the official source, the methodology is public, every verification pass is logged in the changelog, and the full dataset is downloadable (CC BY 4.0).
Not legal advice. This page summarizes Montana's commercial-interest statute for general information, with the verification date shown above — it tells you when we last confirmed the figures, not that they are still current today. Statutes change and courts interpret them; verify the cited statute at the official source, or ask a licensed attorney in your state, before charging or demanding interest.