Idaho Post-Judgment Interest Rate: How to Calculate What You're Owed

Your Idaho judgment doesn't just sit at the same dollar amount while you chase the debtor. Post-judgment interest starts accruing the day the judgment is entered, and it keeps running until every cent is paid. Over a multi-year collection, the interest alone can add hundreds or even thousands of dollars to what you're owed.

Understanding how the rate is set and how to calculate the running total is essential — the court clerk won't do this math for you, and every writ application requires you to state the current balance including accrued interest.

How the Rate Is Set

Idaho's post-judgment interest rate is governed by Idaho Code § 28-22-104. The rate isn't fixed permanently — it's recalculated annually by the Idaho State Treasurer based on the average yield on U.S. Treasury securities. The Treasurer adds 5 percentage points to the weekly average yield on one-year constant maturity U.S. Treasury securities during the second week of June, rounded up to the nearest one-eighth percentage point.

The rate is published each July 1 and applies to judgments entered during the following 12-month period, from July 1 through June 30. For judgments entered from July 1, 2026, through June 30, 2027, the rate is 8.875% per year. A judgment keeps the rate that applied when it was entered.

Judgments entered in prior years continue accruing at the rate that was in effect when the judgment was entered — it doesn't retroactively change.

Calculating Accrued Interest

Post-judgment interest in Idaho accrues as simple interest — not compound. The formula:

Daily accrual = (Unpaid judgment principal × Annual rate) ÷ 365

For example, on a $5,000 judgment at the FY 2027 rate of 8.875%:

• Daily accrual: ($5,000 × 0.08875) ÷ 365 = $1.22 per day
• After 90 days: $109.42 in accrued interest
• After 365 days: $443.75
• After 1,095 days: $1,331.25

When partial payments come in, apply them first to recoverable costs, then accrued interest, and then principal. Recalculate interest on the remaining unpaid principal after the payment.

A proper payment ledger tracks each transaction:

1. Starting balance (original judgment amount)
2. Add any court-approved costs (filing fees, sheriff fees) to the enforceable balance
3. Calculate interest from the last computation date to the payment date
4. Apply the payment — costs first, then interest, then principal
5. Record the new remaining balance
6. Continue interest accrual on the reduced balance

Why It Matters for Enforcement

Every time you file a writ of execution or garnishment, the Application and Affidavit form (SC 9-1 or SC 9-2) requires you to state the exact amount owed. That amount includes:

• Original judgment principal
• Accrued post-judgment interest to date
• Recoverable collection costs (court fees, sheriff fees, recording fees you've paid)
• Minus any payments received

If you overstate the amount, the debtor has grounds to challenge the writ. If you understate it, you're leaving money on the table — the sheriff will stop collecting once the stated amount is reached, even if more interest has accrued since filing.

Interest on Multi-Year Collections

Many Idaho judgments take years to fully collect, especially when the debtor is partially judgment-proof or making installment payments. The interest keeps accruing the entire time — including during a 10-year renewal period for judgments entered on or after July 1, 2015 (or a 5-year period for earlier judgments).

Some practical scenarios:

The judgment-proof debtor who gets a job two years later. Interest has been accruing the entire time. When you finally file a wage garnishment, the balance is the original judgment plus two years of interest plus your enforcement costs.

Voluntary installment payments. If the debtor agrees to pay $200/month, the interest accrual often means the balance decreases more slowly than the debtor expects. Without a proper ledger, disputes about the remaining balance are almost inevitable.

Partial payment from a bank levy. The sheriff sends you $2,400 from a bank levy. That payment reduces the accruing balance, but interest on the remaining amount continues until full satisfaction.

Recording the Final Number

When the judgment is fully satisfied — principal, interest, and all costs — you must file a Satisfaction of Judgment (Form SC 10-1) with the court. The satisfaction should state the total amount collected, including the interest component. Idaho law requires creditors to file this document after full payment; if you do not, the debtor may ask the court to enter a satisfaction.

The Idaho judgment collection guide includes a payment tracking worksheet with the interest calculation formula pre-built, so you can maintain an accurate running balance throughout the collection process.

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