Reference · Idaho · 2026
Idaho late payment interest rate
When your contract sets no rate, the Idaho figure for interest on an overdue B2B invoice is 12%, under Idaho Code § 28-22-104.
"Twelve cents on the hundred by the year" absent an express written contract. Judgments use a treasury-based formula instead.
- Rate
- 12%
- Statute
- Idaho Code § 28-22-104
- Type
- Fixed by statute.
- Source
- legislature.idaho.gov · verified July 9, 2026
What 12% comes to on an unpaid invoice
Simple interest at 12% a year on a 365-day year. Count the days from when interest starts to run in Idaho, which is not always the due date.
| Invoice | 30 days | 60 days | 90 days |
|---|---|---|---|
| $5,000 | $49.32 | $98.63 | $147.95 |
| $10,000 | $98.63 | $197.26 | $295.89 |
| $50,000 | $493.15 | $986.30 | $1,479.45 |
Work out the interest on your invoice
Prefilled with Idaho's legal rate of 12%. If your contract sets a rate, use that instead.
Interest you can claim
$197.26
$10,197.26 with the invoice · $3.29 a day
The ceiling
How high can a late fee go in Idaho?
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.
Idaho'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 Idaho, before writing the common 1.5%-a-month (18%) rate into your terms.
Late payment wording for a Idaho invoice
On your invoice
Payment is due by the date shown on this invoice. Late payments are subject to interest at 12% a year, the legal rate under Idaho Code § 28-22-104.
This restates what Idaho 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 Idaho law sets it.
How Idaho compares
Of the 46 states with a rate that applies on its own, 0 set a higher one and 40 a lower one. The middle of the range is 8%.
Same 12% figure: Massachusetts, Nebraska, Rhode Island, Vermont and Washington.
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 Idaho Code § 28-22-104.