R.I. Gen. Laws § 44-19-11: Deficiency determinations — Interest.

If the tax administrator is not satisfied with the return or returns or the amount of tax paid to the tax administrator by any person, the administrator may compute and determine the amount required to be paid upon the basis of the facts contained in the return or returns or upon the basis of any information in his or her possession or that may come into his or her possession. One or more deficiency determinations may be made of the amount due for one or for more than one month. The amount of the determination, exclusive of penalties, bears interest at the annual rate provided by § 44-1-7 from the fifteenth day (15th) after the close of the month for which the amount, or any portion of it, should have been paid until the date of payment.