Washington late fee law

12%per year

Attaches to the debt by operation of law when you agreed no rate, so it accrues before any lawsuit and can be stated on a demand letter.

IMPORTANT SCOPE LIMIT: RCW 19.52.010(1) reaches only a "loan or forbearance of money, goods, or thing in action". An unpaid trade invoice is ordinarily neither, so do not assume this 12% accrues on it. RCW 19.52.010(2)(a) separately caps prejudgment interest on medical debt at 9%. Verify with counsel.

SCOPE-QUALIFIED. RCW 19.52.010(1) sets 12% per annum, but only for "every loan or forbearance of money, goods, or thing in action" where no different rate is agreed to in writing. An unpaid trade invoice is ordinarily neither a loan nor a forbearance, so this 12% should NOT be assumed to accrue on an overdue B2B invoice; whether ordinary trade credit is a "forbearance" is unresolved. Carve-out: RCW 19.52.010(2)(a) provides that prejudgment interest on MEDICAL DEBT must not exceed 9% per annum. Verified on the official Washington Legislature site (app.leg.wa.gov). Verify with counsel before charging 12% on an invoice.

Parties may agree in writing to a rate. The usury ceiling is at RCW 19.52.020 (reported as the higher of 12% per annum or 4 percentage points above the average 26-week Treasury bill coupon-issue yield) - NOT re-verified against the primary source in this pass, so treat the ceiling figure as unconfirmed. The ceiling is in any event largely inapplicable to B2B credit: under RCW 19.52.080 corporations, partnerships, trusts, associations, joint ventures and governments may not plead usury, and no one may assert usury where the transaction was primarily for agricultural, commercial, investment or business purposes (consumer transactions retain protection). Verify with counsel.

public+private-construction

PUBLIC (RCW ch. 39.76): state agencies and all local public bodies must pay within 30 days of receipt of a proper invoice or of the goods/services, whichever is later; overdue amounts accrue interest at 1% per month (minimum $1 per month) (RCW 39.76.011). Exceptions include good-faith disputes and interagency transactions. PRIVATE CONSTRUCTION (RCW ch. 60.30, enacted 2023 c 373 (SB 5528) and AMENDED BY 2024 c 101 - the history note reads [2024 c 101 s 1; 2023 c 373 s 1], so citing SB 5528 alone is incomplete): applies expressly to private construction contracts (RCW 60.30.030), with a carve-out for single-family residential projects of fewer than 12 units. RCW 60.30.010(1) caps retainage at 5% of the contract price. RCW 60.30.010(2) provides 1% per month interest on FINAL PAYMENT, commencing 30 days after the owner accepts the work, alongside a 15-day accept-or-identify mechanism and a pay-when-paid limiter for subcontractors. Verified at app.leg.wa.gov.

No distinctive Washington statute on flat late fees for ordinary commercial invoices was found; default principles apply - an agreed late fee is enforceable if reasonable under the liquidated-damages/penalty doctrine, and the business-purpose bar on usury claims (RCW 19.52.080) removes most usury-recharacterisation risk for B2B late charges. On PRIVATE CONSTRUCTION contracts, RCW ch. 60.30 supplies a statutory 1%/month baseline on final payment and caps retainage at 5%. Verify with counsel.