Interest on unpaid invoices in Washington: 12% a year if no rate was agreed; the most you can set depends on the deal

Washington's rate when no rate was agreed

12% a year. The 12 percent per annum is for a loan or forbearance of money, goods, or thing in action where no different rate is agreed to in writing between the parties (RCW 19.52.010(1)). It depends: see RCW 19.52.010.

• “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” — RCW 19.52.010(1), read November 6, 2026

The most you can set in Washington

For a homeowner: The higher of 12% a year or 4 percentage points above the 26-week Treasury bill yield (published monthly; 12.00% for November 2026). General usury cap, RCW 19.52.020. Consumer installment sales of goods/services under the Retail Installment Sales Act (chapter 63.14) carry their own agreed-and-disclosed service charge rules (RCW 63.14.130). It depends: see RCW 19.52.020, 63.14.130.

For a business customer: Effectively no usury limit: businesses/entities and transactions primarily for business, commercial, investment or agricultural purposes cannot plead usury. RCW 19.52.080 — corporations, partnerships, etc. may not plead usury, nor may persons in transactions primarily for business purposes.

• “any rate of interest shall be legal so long as the rate of interest does not exceed the higher of: (a) Twelve percent per annum; or (b) four percentage points above the equivalent coupon issue yield (as published by the Board of Governors of the Federal Reserve System) of the average bill rate for twenty-six week treasury bills” — RCW 19.52.020(1), read November 6, 2026
• “The maximum allowable interest rate applicable for the month of November 2026 pursuant to RCW 19.52.020 is twelve point zero percent (12.00%) per annum.” — Washington State Register — State Maximum Interest Rate (computed and filed by the State Treasurer under RCW 19.52.025), read November 6, 2026
• “The service charge, in a retail installment contract, shall not exceed the dollar amount or rate agreed to by contract and disclosed under RCW 63.14.040 (1)(h).” — RCW 63.14.130(1), read November 6, 2026
• “persons may not plead the defense of usury nor maintain any action thereon or therefor if the transaction was primarily for agricultural, commercial, investment, or business purposes: PROVIDED, HOWEVER, That this section shall not apply to a consumer transaction of any amount.” — RCW 19.52.080, read November 6, 2026
• “Profit and nonprofit corporations, Massachusetts trusts, associations, trusts, general partnerships, joint ventures, limited partnerships, and governments and governmental subdivisions, agencies, or instrumentalities may not plead the defense of usury” — RCW 19.52.080, read November 6, 2026

Late fees in Washington

What the text says: Under the Retail Installment Sales Act: delinquency charges only if the contract/charge agreement provides for them and they are reasonable; on a retail charge account under $100 average balance, paid within 10 days after due, the charge is capped at 10% of the average balance (minimum up to $2). Consumer retail installment contracts, retail charge agreements and lender credit cards (RCW 63.14).

• “The holder of any retail installment contract, retail charge agreement, or lender credit card agreement may not collect any delinquency or collection charges, including any attorney's fee and court costs and disbursements, unless the contract, charge agreement, or lender credit card agreement so provides. In such cases, the charges shall be reasonable” — RCW 63.14.090(1), read November 6, 2026
• “where the minimum payment is received within the ten days following the payment due date, delinquency charges for the late payment of a retail charge agreement or lender credit card agreement may not be more than ten percent of the average balance of the delinquent account for the prior thirty-day period when the average balance of the account for the prior thirty-day period is less than one hundred dollars, except that a minimum charge of up to two dollars shall be allowed.” — RCW 63.14.090(3), read November 6, 2026
• “"Services" means work, labor, or services of any kind when purchased primarily for personal, family, or household use and not for commercial or business use whether or not furnished in connection with the delivery, installation, servicing, repair, or improvement of goods and includes repairs, alterations, or improvements upon or in connection with real property” — RCW 63.14.010(16), read November 6, 2026

Does Washington want it agreed in advance?

Agreed in advance: yes, in the cases below. Under RISA, delinquency or collection charges cannot be collected unless the contract or charge agreement so provides (RCW 63.14.090).

• “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” — RCW 19.52.010(1), read November 6, 2026
• “The holder of any retail installment contract, retail charge agreement, or lender credit card agreement may not collect any delinquency or collection charges, including any attorney's fee and court costs and disbursements, unless the contract, charge agreement, or lender credit card agreement so provides. In such cases, the charges shall be reasonable” — RCW 63.14.090(1), read November 6, 2026

Homeowners and businesses in Washington

A consumer transaction (primarily personal, family, or household) keeps the usury cap of RCW 19.52.020; business-purpose transactions and business entities cannot plead usury. Under RCW 63.14.010(16), services means work, labor, or services purchased primarily for personal, family, or household use and not for commercial or business use.

• “persons may not plead the defense of usury nor maintain any action thereon or therefor if the transaction was primarily for agricultural, commercial, investment, or business purposes: PROVIDED, HOWEVER, That this section shall not apply to a consumer transaction of any amount.” — RCW 19.52.080, read November 6, 2026
• “Consumer transactions, as used in this section, shall mean transactions primarily for personal, family, or household purposes.” — RCW 19.52.080, read November 6, 2026
• “"Services" means work, labor, or services of any kind when purchased primarily for personal, family, or household use and not for commercial or business use whether or not furnished in connection with the delivery, installation, servicing, repair, or improvement of goods and includes repairs, alterations, or improvements upon or in connection with real property” — RCW 63.14.010(16), read November 6, 2026

Prompt payment on private construction in Washington

Not found in our check for Washington.

Work out a late charge in Washington

Starts at Washington's 12%, the rate when none was agreed, not a maximum.

What was not checked for Washington

• No Washington prompt-payment law for private construction was found, only public-works ones (RCW 39.04.250, chapter 39.76); no text read confirms there is none.

Check Washington's own text

Before you charge: read RCW 19.52.010(1) and the other Washington texts quoted on this page, or ask a lawyer. As of November 6, 2026.

This is a plain-words summary of each state's own laws as of November 6, 2026, not legal advice. Rules have exceptions. Check the state's own text, linked on every state's page, or a lawyer before you charge a late fee or interest.

Compare Washington with every state's answer, or with its neighbours just below.

Next door to Washington

• Idaho: 12% if none agreed, no general cap found
• Oregon: 9% if none agreed, depends by agreement

Official sources for Washington

• RCW 19.52.010(1) — read November 6, 2026
• RCW 19.52.020(1) — read November 6, 2026
• Washington State Register — State Maximum Interest Rate (computed and filed by the State Treasurer under RCW 19.52.025) — read November 6, 2026
• RCW 63.14.130(1) — read November 6, 2026
• RCW 19.52.080 — read November 6, 2026
• RCW 63.14.090(1) — read November 6, 2026
• RCW 63.14.010(16) — read November 6, 2026

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