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 Montana, 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 is often set by law. In Montana, the prejudgment interest rate is typically based on the contract rate if one exists, or otherwise at a rate determined by statute, which can vary. Post-judgment interest is the interest that accrues after a judgment has been entered by the court. In Montana, the post-judgment interest rate is set by statute, which is 10% per annum unless the judgment is based on a contract that specifies a different rate. It's important to note that these rates are subject to change through legislative action, and the specific details of the judgment, such as the date of entry and the nature of the judgment, may affect the applicable interest rate. Attorneys in Montana would analyze the relevant statutes and case law to determine the correct application of interest rates to a particular judgment.