Washington Late Fee Calculator
Calculate late fees and interest on overdue invoices in Washington — pre-set to the state's 12% statutory default rate.
Late fee rules in Washington
Statutory interest rate
12% per year where no different rate is agreed in writing. The default judgment rate floats at the statutory maximum (the higher of 12% or 4 points above the 26-week T-bill yield, updated monthly), with the contract rate applying to written-contract judgments.
RCW 19.52.010 (default rate); RCW 4.56.110 (judgments); RCW 19.52.020 (maximum)
Can you charge more? (contract & caps)
Washington's usury ceiling nominally caps interest at the higher of 12% or T-bill + 4 points, but corporations, LLCs, and partnerships cannot raise usury on business-purpose transactions (RCW 19.52.080) — so for B2B invoices the written contract effectively controls.
Prompt payment rules
Public bodies must pay 1% per month (minimum $1/month) on late payments under written contracts for public works, goods, services, and equipment (RCW 39.76.011, 30-day clock). Washington has no general private-construction prompt-payment act.
Worth knowing
The default judgment rate is pegged to the statutory maximum as of the date of entry — in high-rate environments Washington judgments can bear more than 12%.
This page is general information, not legal advice. Statutory rates change — some reset annually or quarterly — and how they apply depends on your contract and situation. Verify current rates against the cited statutes or consult a lawyer before charging interest.
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