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 South Dakota, interest rates on judgments are governed by state law, which sets forth the rates for both prejudgment and post-judgment interest. Prejudgment interest is the interest accrued from the time the money is owed until a judgment is entered. South Dakota Codified Laws (SDCL) 21-1-13.1 specifies that unless there is a written agreement specifying a different rate, prejudgment interest is calculated at the Category B rate, which is determined by the state treasurer and can change annually. Post-judgment interest, on the other hand, is interest that accrues after a judgment has been entered by the court. According to SDCL 21-1-13, the post-judgment interest rate is also set at the Category B rate as determined by the state treasurer. It is important to note that these rates are subject to change and may vary depending on the specific circumstances of the case, so consulting with an attorney for the most current rates and calculations is advisable.