LATE FEE TOOL
Illinois late fee calculator
5 percent if the writing states no rate. 9 percent unless the debt is a business loan.
By Abass Gass, Founder of Incusia.
October 4, 2026 · 6 min read
Last updated October 4, 2026
Leave this blank and keep the box checked if the invoice is still unpaid. The day count then runs through today.
1.5% a month is the national standard for a written commercial term. It is 18% a year of simple interest. Use it only if your contract already says so.
Days after the due date before interest starts. Use 0 if your terms have no grace period.
- Days overdue
- Add dates
- Interest accrued
- $0.00
- Daily rate and arithmetic
- Daily rate: 0.0493% of the invoice. Enter an amount and a due date to see the arithmetic.
- Total now owed
- $0.00
18% a year is above the 9% written contract rate in 815 ILCS 205/4. A business loan is exempt from that cap. A late fee on an invoice to a business can fit the exemption. If the debtor is not operating a business, stay at 9%.
Illinois invoice interest rate and the business loan exemption
Illinois looks strict until you read the exception that freelancers actually live in. 815 ILCS 205/4 says parties to a written contract may agree to 9 percent a year. The same section then says it is lawful to contract for interest on a business loan to a business association, a partnership, a sole proprietor operating a business, or a similar venture. A loan secured only by someone's wages or household goods is carved back out. A late fee on an invoice to a client who is running a business is the fact pattern that exemption was written for. 1.5 percent a month is 18 percent a year, which is over 9 percent, so you are relying on that exemption. If the debtor is not operating a business, stay at 9 percent. I would not describe a personal favor as a business loan to get a higher rate.
When the paper states no rate, section 205/2 allows 5 percent a year on a bond, bill, promissory note, or other instrument of writing, and on money due on the settlement of an account from the day the balance is settled. That is the silent invoice, not 1.5 percent. You have a long time to sue, and that is the Illinois fact people underuse. A written contract action is 10 years under 735 ILCS 5/13-206. Small claims is a contract or tort claim for money not over $10,000, exclusive of interest and costs, under Supreme Court Rule 281. The State Prompt Payment Act, 30 ILCS 540, binds state agencies. The Contractor Prompt Payment Act, 815 ILCS 603, is about construction contracts. Neither one sets the fee on a branding invoice. Write the business rate into the terms, keep the debtor inside the exemption, and do not wait nine years just because the statute lets you.
Illinois invoice late fee figures
- Default legal rate
- 5% a year on a written instrument or a settled account (815 ILCS 205/2)
- Statutory cap
- 9% in a written contract, but a business loan is exempt (815 ILCS 205/4). There is no separate cap for that exempt business loan.
- Small claims limit
- $10,000, not counting interest and costs (Ill. Sup. Ct. R. 281)
- Statute of limitations
- 10 years on a written contract (735 ILCS 5/13-206)
Frequently asked questions
Not when the business loan exemption applies. 815 ILCS 205/4 allows 9 percent in a written contract and then exempts a business loan to a corporation, partnership, sole proprietor operating a business, or similar venture. A late fee on an invoice to that kind of client can be above 9 percent, which is how 1.5 percent a month gets used. The exemption does not cover a loan secured only by an individual's wages or household goods. If you cannot describe the debtor as a business, charge no more than 9 percent.
Five percent a year. Section 205/2 says creditors may receive 5 percent on money after it becomes due on a bond, bill, promissory note, or other instrument of writing, and on a settled account from the day the balance is ascertained. An invoice can be that instrument. It is not an invitation to charge 9 percent, and it is not 1.5 percent a month. The 9 percent figure is what you may agree to. The 5 percent figure is what you get for agreeing to nothing.
Ten years. 735 ILCS 5/13-206 says actions on written contracts and other written evidence of indebtedness shall be started within 10 years after the cause of action accrued. A written payment or a new written promise can extend the time, on the statute's terms. Ten years is long enough to lose every email. It is also long enough that a client may have changed banks, names, and states. File while the people who approved the work still work there. The statute is a backstop, not a collection strategy. Interest at 5 percent for a decade is a sad judgment.
Ten thousand dollars, exclusive of interest and costs. Supreme Court Rule 281 defines a small claim as a civil action based on tort or contract for money not in excess of that amount. The $10,000 figure has been in the rule since cases filed after the 2006 change, and later amendments did not lower it. Interest you add does not, by itself, push a $9,000 invoice out of small claims, because interest is excluded. Costs are excluded too. If the principal is over $10,000, you are in a regular civil action, still with the 10 year written contract statute.
I would not, unless a lawyer reads your clause against the Interest Act and says the business exemption carries it. Compounding is how a stated 1.5 percent becomes a higher annual rate than the client thinks they agreed to. The exemption in section 205/4 is about contracting for interest on a business loan. It is not a suggestion to stack fees on fees until the number looks like punishment. This calculator uses simple interest and shows the formula. If you cannot explain the formula in one line in the reminder, do not send it.
No. 815 ILCS 603 is the Contractor Prompt Payment Act, and it is about construction contracts. The State Prompt Payment Act, 30 ILCS 540, is about bills to the state. A designer invoicing a private company is in neither statute. Your rate is section 205/2 if the paper is silent, or the written rate if the business loan exemption fits. Do not cite 815 ILCS 603 in a demand for a brand project. If you actually performed construction contracting, read 603 before you use the generic calculator note on this page. The title 'prompt payment' is not enough.
Yes. Section 205/2 is what writing gets you when it states no rate: 5 percent. Section 205/4 is about a rate stipulated in a written contract, including the business loan language. A rate above 5 percent that appears for the first time in a collection email was not stipulated. Write it on the invoice or the master terms the client already has. If you are relying on the business exemption to exceed 9 percent, the writing should make clear this is a charge on a business account.
You can add the 5 percent that section 205/2 already allows, and you should show the math. You should not add 1.5 percent a month that the invoice did not contain. The client received an instrument of writing. That instrument is what the statute prices when it is silent. Send a revised balance at 5 percent, with the days and the daily rate, and a date you will still take the original amount. Then amend your template. Chasing a fee you invented is slower than chasing the principal, because you gave them a real objection.
Stay inside the non exempt rates. The business loan exemption in section 205/4 is for a commercial, agricultural, or industrial enterprise carried on for profit. It is not for a person buying something for their household. A wedding photographer's client, or anyone paying personally, is a bad place to test 1.5 percent a month. Use 9 percent only if a written contract allows it, and 5 percent if the writing states no rate. Consumer debts also have their own judgment interest rules under 735 ILCS 5/2-1303. Do not borrow a B2B rate for a household bill.
This is general information, not legal advice. Statutes change and the correct treatment depends on your contract and circumstances. Consult a qualified professional for your situation.
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