Illinois Late Fee Calculator
Work out interest on an overdue B2B invoice under Illinois law. The legal default rate — what applies when the contract is silent — is 5%, and the statute is quoted verbatim below. All math runs locally in your browser.
Statutory legal rate on written instruments and money wrongfully withheld when no rate is agreed.
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 Illinois's statute (815 ILCS 205/2, 205/4) for you.
What Illinois law actually says
Creditors shall be allowed to receive at the rate of five (5) per centum per annum for all moneys after they become due on any bond, bill, promissory note, or other instrument of writing; on money lent or advanced for the use of another; [...] and on money withheld by an unreasonable and vexatious delay of payment.
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 Illinois — written B2B contracts
No statutory cap
9% nominal cap, but any loan to a corporation and any business-purpose loan may bear any agreed rate. Ordinary B2B credit is effectively uncapped.
Basis: 815 ILCS 205/4(1)(a),(c). 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 Illinois'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
Illinois'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.
Illinois late fee FAQ
Can I charge late fees on overdue invoices in Illinois?
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: 5%. Statutory legal rate on written instruments and money wrongfully withheld when no rate is agreed. Statute: 815 ILCS 205/2, 205/4, verified 2026-08-19. Consumer and rent debts follow separate laws.
What is the maximum late fee I can charge in Illinois?
For a written B2B contract: 9% nominal written-contract ceiling — but business/commercial credit is broadly exempt (any agreed rate). Basis: 815 ILCS 205/4(1)(a),(c). 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 Illinois?
The statutory default rate of 5%. Statutory legal rate on written instruments and money wrongfully withheld when no rate is agreed. Statute: 815 ILCS 205/2, 205/4 (verbatim quote on this page, verified 2026-08-19).
Does this cover rent, apartment, or consumer late fees in Illinois?
No. This page covers business-to-business invoices only. Residential rent late fees are governed by Illinois'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 — Illinois'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 Illinois'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.