Interest rates are compensation for the time-value of money, and are calculated on judgments (the amount of money one party to a lawsuit is ordered to pay another party) based on the applicable state or federal statutes. There are often different interest rates set by law for prejudgment interest (the interest on the amount owed before the judgment) and post-judgment interest (the interest on the amount owed after the judgment). The calculation of prejudgment and post-judgment interest rates vary from state to state (and in federal court), and require a careful analysis of the statutes.

In Idaho, interest rates on judgments are governed by state statutes. Prejudgment interest is the interest accrued from the time the money is owed until a judgment is entered, and its rate can be either agreed upon by the parties as stipulated in a contract or, if there is no agreement, the rate is set by statute. Idaho Code § 28-22-104(1) provides that the legal rate of interest when there is no express contract in writing fixing a different rate is 12% per annum. Post-judgment interest refers to the interest that accrues on the amount of the judgment from the date the judgment is entered until it is paid. According to Idaho Code § 28-22-104(2), the rate of post-judgment interest is 5% per annum above the average rate of interest earned on investments in the state's pooled investment fund during the previous fiscal year, unless the judgment is based on a contract specifying a different rate. It's important to note that these rates are subject to change, and one should review the current statutes or consult with an attorney for the most up-to-date information.