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 Arizona, interest rates on judgments are governed by state statutes. Prejudgment interest refers to the interest that accrues from the time the money is owed until a judgment is entered, while post-judgment interest accrues from the time the judgment is entered until the amount is paid. As of the knowledge cutoff in 2023, Arizona law sets the legal rate of interest at 10% per annum unless a different rate is contracted for in writing. For judgments arising out of written contracts that specify an interest rate, that rate will apply until the judgment is paid. Post-judgment interest rates are typically the same as the prejudgment rate unless specified otherwise by the court or by statute. It is important to note that these rates are subject to change through legislative action, and an attorney can provide the most current information and assist in the calculation of interest on judgments.