Washington late fee and interest rules for invoices

Here is what Washington law says about late fees and interest on unpaid invoices, for business clients and consumers, with the statute and a link to the official source.

This is general information, not legal advice. Laws change and can apply differently to your situation, so check your state's current law or ask a lawyer before you charge a late fee, interest or a deposit. Last reviewed October 21, 2026.

Washington late fee and interest limits

Rule	Washington
Business-to-business late fee or interest cap	No set limit for business transactions; charge the rate agreed in writing.
Consumer cap	Interest is capped at the higher of 12% a year or 4 points above the 26-week Treasury bill rate. Interest on medical bills is capped at 9%.
Legal interest rate when no rate was agreed	12% a year unless a different rate was agreed in writing.
Statute	RCW 19.52.010, 19.52.020, 19.52.080
Last reviewed	October 21, 2026

Late fee wording to copy

Agree on the fee before the work starts and show it on every invoice.

Payment is due within 30 days of the invoice date. Balances unpaid after the due date are charged interest of [rate]% per month.
A late fee of $[amount] applies to any balance not paid by the due date.
Past due balances accrue interest at [rate]% per year, or the highest rate allowed by law, whichever is lower.

Keep going

Late fee calculatorWork out the fee or interest on an overdue invoice.How to charge late feesHow to set a late fee and put it on your invoices.Late fee laws by stateEvery state in one table.