Washington Post-Judgment Interest Rate and How to Calculate It

Every day a Washington judgment goes unpaid, the balance grows. Post-judgment interest accrues automatically from the date of entry, and it's the creditor's job to calculate it correctly when filing garnishments, demanding payment, or recording satisfaction.

The Statutory Rate

RCW 4.56.110 sets the rate by judgment type; 12% is not universal. Consumer-debt judgments bear 9%, private student-loan judgments bear two percentage points above prime, tort judgments use statutory Treasury-bill or prime-rate formulas, and other judgments bear the maximum rate under RCW 19.52.020. Interest accrues from entry until satisfaction.

Common rate categories include:

Contract-based judgments — A judgment founded on a written contract that provides for interest until paid bears the specified contract rate only if that rate is set forth in the judgment.

Tort judgments — Judgments for tortious conduct by a public agency use the Treasury-bill formula in RCW 4.56.110; other tort judgments use two percentage points above prime.

Consumer debt and private student loans — Consumer-debt judgments bear 9%. Private student-loan judgments use two percentage points above prime under RCW 4.56.110.

How to Calculate Daily Interest

The formula is straightforward:

Annual interest at 12% = Principal judgment × 0.12

Daily interest at 12% = Annual interest ÷ 365

For a $5,000 judgment bearing a 12% rate:

• Annual interest: $5,000 × 0.12 = $600
• Daily interest: $600 ÷ 365 = $1.64 per day

After 90 days: $5,000 + ($600 × 90 ÷ 365) = $5,147.95 After one year: $5,000 + $600 = $5,600 After three years: $5,000 + $1,800 = $6,800

Interest on the Full Balance, Not Just Principal

Interest accrues on the original judgment amount. Enforcement costs added to the judgment under RCW 12.40.105 — certification fees, garnishment filing fees, process service costs — are recoverable but typically tracked separately. The statutory interest applies to the principal judgment as entered by the court.

When you file a garnishment writ or payment demand, itemize the balance clearly: principal judgment, accrued interest calculated to the date, and recoverable enforcement costs. Courts and employers expect this breakdown.

Partial Payments

When the debtor makes partial payments, apply them in this order: first to accrued enforcement costs, then to accrued interest, and finally to the principal balance. Interest continues accruing on the remaining principal after each partial payment is credited.

Example: On a $5,000 judgment with $300 in accrued interest and $40 in filing fees, a $500 partial payment covers the $40 in fees, then $300 in interest, then reduces the principal to $4,840. Going forward, daily interest is calculated on $4,840.

Why This Matters for Collection

At a 12% simple interest rate, a judgment grows meaningfully over time. A $10,000 judgment becomes $12,000 after one year and $22,000 after ten years. Combined with Washington's 10-year judgment lifespan (extendable to 20 years under RCW 6.17.020), the interest creates a financial incentive for debtors to settle sooner rather than later — and a real recovery for creditors who are patient.

When you file for garnishment, the writ application includes the total amount owed. Calculate interest to the date you file, not to the date of the original judgment. When satisfaction is eventually filed, calculate interest through the actual date of final payment.

The Washington judgment collection guide includes an interest calculation worksheet and enforcement cost tracker that handles partial payments and running balances automatically.

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