Reference · Montana · 2026
Montana late payment interest rate
When your contract sets no rate, the Montana figure for interest on an overdue B2B invoice is 10%, under Mont. Code § 31-1-106.
On instruments of writing, accounts stated, and settlements of account from the date the balance is ascertained.
- Rate
- 10%
- Statute
- Mont. Code § 31-1-106
- Type
- Fixed by statute.
- Source
- archive.legmt.gov · verified July 9, 2026
What 10% comes to on an unpaid invoice
Simple interest at 10% a year on a 365-day year. Count the days from when interest starts to run in Montana, which is not always the due date.
| Invoice | 30 days | 60 days | 90 days |
|---|---|---|---|
| $5,000 | $41.10 | $82.19 | $123.29 |
| $10,000 | $82.19 | $164.38 | $246.58 |
| $50,000 | $410.96 | $821.92 | $1,232.88 |
Work out the interest on your invoice
Prefilled with Montana's legal rate of 10%. If your contract sets a rate, use that instead.
Interest you can claim
$164.38
$10,164.38 with the invoice · $2.74 a day
The ceiling
How high can a late fee go in Montana?
Your contract decides. The rate above only applies when your terms are silent. Between businesses, an agreed late-interest rate or late fee replaces it, within two limits: the state's ceiling on agreed rates, and the rule that a late fee must compensate you rather than punish the customer.
Montana's ceiling on an agreed rate wasn't part of our verified research, so check the state's usury law, or ask a lawyer licensed in Montana, before writing the common 1.5%-a-month (18%) rate into your terms.
Late payment wording for a Montana invoice
On your invoice
Payment is due by the date shown on this invoice. Late payments are subject to interest at 10% a year, the legal rate under Mont. Code § 31-1-106.
This restates what Montana law applies when your contract is silent. If your contract sets a rate, quote that instead. The wording doesn't say when interest starts, because that differs by state; the note at the top of this page covers it where Montana law sets it.
How Montana compares
Of the 46 states with a rate that applies on its own, 7 set a higher one and 33 a lower one. The middle of the range is 8%.
Same 10% figure: Arizona, California, Hawaii, Kansas and Utah.
Interest is the fallback. Getting paid on time is the plan.
DueTrail turns overdue invoices into managed cases with reviewable reminders and recorded promises to pay, so invoices get settled before anyone reaches for Mont. Code § 31-1-106.