Washington Late Fee Calculator
Work out interest on an overdue B2B invoice under Washington law. The legal default rate — what applies when the contract is silent — is 12%, and the statute is quoted verbatim below. All math runs locally in your browser.
Legal rate where no different rate is agreed in writing; applied as prejudgment interest on liquidated claims.
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 Washington's statute (RCW 19.52.010, 19.52.020) for you.
What Washington law actually says
(1) Except as provided in subsection (2) of this section, every loan or forbearance of money, goods, or thing in action shall bear interest at the rate of twelve percent per annum where no different rate is agreed to in writing between the parties [...]
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 Washington — written B2B contracts
No statutory cap
Business entities can't plead usury, and no one may plead it for a commercial/business/investment/agricultural-purpose deal — so B2B may exceed the 12% floating cap freely.
Basis: RCW 19.52.080. 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 Washington'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
Washington'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.
Washington late fee FAQ
Can I charge late fees on overdue invoices in Washington?
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: 12%. Legal rate where no different rate is agreed in writing; applied as prejudgment interest on liquidated claims. Statute: RCW 19.52.010, 19.52.020, verified 2026-08-19. Consumer and rent debts follow separate laws.
What is the maximum late fee I can charge in Washington?
For a written B2B contract: Floating cap: higher of 12% or 26-week T-bill average +4 pts — business transactions are exempt (any agreed rate). Basis: RCW 19.52.080. 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 Washington?
The statutory default rate of 12%. Legal rate where no different rate is agreed in writing; applied as prejudgment interest on liquidated claims. Statute: RCW 19.52.010, 19.52.020 (verbatim quote on this page, verified 2026-08-19).
Does this cover rent, apartment, or consumer late fees in Washington?
No. This page covers business-to-business invoices only. Residential rent late fees are governed by Washington'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 — Washington'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 Washington'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.