Idaho is quietly one of the best states in this series to send an invoice from. Its default interest rate is 12% a year — higher than any neighbor — there's no general cap on a rate you write into a contract, and a fee-shifting statute can make a client who refuses to pay cover your lawyer. Here's what Idaho freelancers and small businesses need to know.
Idaho Late Fee Calculator
Quick estimate at the standard 1.5%/month rate — Idaho has no general cap on a written rate. For grace periods, flat fees, and a PDF invoice, use the full late fee calculator.
No Late Fee Clause? Idaho Still Gives You 12% a Year
Under Idaho Code § 28-22-104, interest is allowed at 12% per annum on money due by express contract and on money after it becomes due. That's one of the most generous statutory default rates anywhere — Utah and Arizona use 10%, Oregon 9%. If your contract says nothing about late fees, an overdue invoice still carries 12% a year from the due date.
The open-account catch. The same statute treats open accounts — ongoing work billed as you go, without a fixed contract for the job — differently: interest runs only after three months from the date of the last item. A signed contract or accepted proposal with a due date avoids the wait. One more reason to get the engagement in writing.
Is There a Cap on a Written Late Fee in Idaho?
Idaho has no general statutory ceiling on an interest rate agreed in writing. So the national-standard 1.5% a month (18% a year) is on solid ground for a written freelance contract — and that's what the calculator above defaults to.
That nearly changed. House Bill 649 (2026) would have capped agreed rates at the greater of 30% or 10 points above prime. It cleared committee in early March, was sent back to committee on March 25, 2026, and did not become law. Even if a cap like that returns, it would sit far above any normal invoice late fee. The practical limit is the same as everywhere: a charge large enough to look like punishment rather than compensation — particularly one stated per day — can be struck as a penalty. See is a daily late fee legal on an invoice.
Idaho Can Make the Client Pay Your Attorney
This is the Idaho rule that changes the economics of collecting. Under Idaho Code § 12-120(3), the prevailing party in a civil action on an open account, an account stated, a contract relating to the purchase or sale of services, or any commercial transaction is awarded reasonable attorney's fees. "Commercial transaction" covers everything except personal or household purchases — so an invoice to a business client is squarely in.
- It cuts both ways. If the client wins, they recover their fees from you. File when your contract, invoices and delivery records are clean.
- Smaller claims have a second route. § 12-120(1) awards fees on claims of $35,000 or less if you made a written demand at least 10 days before filing — but not if the client had already offered at least 95% of what the court awards.
- Say so in your demand letter. A client who realizes that refusing to pay could mean paying two lawyers often settles before anyone files.
Idaho Small Claims: $5,000, No Lawyers
Small claims in Idaho is a department of the magistrate division of district court, with a ceiling of $5,000 (Idaho Code § 1-2301). Lawyers can't represent either side, so it's built for you to file yourself. Above $5,000 you'd file a regular civil case — which is where § 12-120 makes hiring a lawyer far easier to justify. Is it worth suing a client over an unpaid invoice runs that trade-off against your own time.
How Idaho Compares to Its Neighbors
Scroll sideways to see all columns
| State | Rate rule | Small claims limit |
|---|---|---|
| Idaho | 12%/yr default; no general cap on a written rate | $5,000 |
| Utah | 10%/yr default; any agreed rate allowed | $20,000 (to $25,000 in 2030) |
| Oregon | 9%/yr default; no commercial ceiling once written | $10,000 |
| Washington | No cap on commercial late fees once written | $10,000 |
| Nevada | Prime + 2% default (floating); no commercial ceiling once written | $10,000 |
Idaho has the highest no-contract default of its neighbors and a fee-shifting statute most of them lack, but the lowest small claims ceiling. Boise-area freelancers often bill clients in Washington, Oregon or Utah — see the Washington, Oregon and Utah guides for the other side of the line.
Setting Up Enforceable Late Fees in Idaho
- Write the rate into the contract — 1.5% a month is standard and uncapped in Idaho.
- Use a signed contract or accepted proposal with a due date, so interest isn't delayed by the open-account rule.
- Keep a clean paper trail. Under § 12-120 the winner's lawyer gets paid — make sure that's you.
- Send a written demand at least 10 days before filing on any claim of $35,000 or less.
Collecting in Idaho
- Small claims (magistrate division): up to $5,000; attorneys not permitted (§ 1-2301)
- Attorney's fees to the prevailing party on services contracts and commercial transactions (§ 12-120(3)); on claims of $35,000 or less after a 10-day written demand (§ 12-120(1))
- Default interest: 12% a year on money due by contract (§ 28-22-104); on open accounts, after three months from the last item
- Statute of limitations: 5 years for written contracts (§ 5-216), 4 years for oral contracts (§ 5-217)
Need to calculate exactly what your Idaho client owes with late fees included? Get the updated total instantly.
Calculate Late Fees →Idaho is one of the stronger states to invoice from: 12% a year even without a clause, no cap on a written rate, and a statute that puts the attorney's fees on whoever loses a commercial dispute. Write your rate and due date into a signed agreement, keep your records clean, and lead your demand letter with § 12-120.
Frequently Asked Questions
Is there a free Idaho late fee calculator? +
Yes. The quick calculator above estimates the fee at the common 1.5% a month. For grace periods, flat fees and a downloadable PDF, use GetSoloTools' full late fee calculator.
What interest can I charge in Idaho if my contract doesn't mention a late fee? +
12% a year. Idaho Code § 28-22-104 allows interest at 12% per annum on money due by express contract and on money after it becomes due. That is one of the highest statutory default rates in the country. One catch: on an open account (ongoing work billed without a fixed contract), interest runs only after three months from the date of the last item.
Is there a cap on late fees in Idaho? +
Idaho has no general statutory ceiling on a rate agreed in a written contract, so the common 1.5% a month is on solid ground. A 2026 bill (House Bill 649) proposed capping agreed rates at the greater of 30% or prime plus 10 points, but it was sent back to committee in March 2026 and did not become law. A very aggressive fee can still fail as an unenforceable penalty.
Can I recover attorney's fees for an unpaid invoice in Idaho? +
Often, yes. Idaho Code § 12-120(3) awards reasonable attorney's fees to the prevailing party in a civil action on an open account, an account stated, a contract for services, or any commercial transaction, meaning any transaction that is not for personal or household purposes. It works both ways: if the client wins, the client gets fees, so file only when your paperwork is solid. Section 12-120(1) separately allows fees on claims of $35,000 or less if you made a written demand at least 10 days before suing.
What is the small claims limit in Idaho? +
$5,000, heard by a magistrate in the small claims department of the district court (Idaho Code § 1-2301). Attorneys may not represent parties in Idaho small claims. Statute of limitations is 5 years for a written contract (§ 5-216) and 4 years for an oral one (§ 5-217).