SDCL § 54-3A-12: Imposition and collection of delinquency charge.

The holder of a contract authorized by this chapter may, if the contract so provides, collect a delinquency and collection charge on each installment in arrears for a period of not less than ten days in an amount not in excess of five percent of each installment or five dollars, whichever is greater.

Any delinquency or collection charge may be collected only once on any one installment however long the installment remains delinquent.