If any tax or penalty imposed by this Chapter is not paid on or before the date prescribed for such payment, in addition to such tax and penalties, interest on the unpaid balance of the tax and penalties at an annual rate established under this Section, shall be collected for the period from its due date until the date it is paid.

(a) Determination of Rate of Interest. The annual rate established under this Section shall be such adjusted rate as established by the Tax Commissioner.

(b) Establishment of Adjusted Rate. If the adjusted prime rate charged by banks, rounded to the nearest full percent, during the six-month period ending September 30 of any calendar year, or during the six-month period ending on March 31 of any calendar year, differs from the interest rate in effect under this Section on either such date, respectively, then the Tax Commissioner shall establish, within fifteen (15) days after the close of the applicable six-month period, an adjusted rate of interest equal to such adjusted prime rate.

(c) Effective date of Adjustment. Any adjusted rate of interest established under Subsection (b) of this Section shall be effective on January 1 of the succeeding year in the case of an adjustment attributable to the six-month period ending on September 30 and on July 1 of the same year in the case of an adjustment attributable to the six-month period ending on March 31.

(d) Definition of Prime Rate. For purposes of this Section, the term adjusted prime rate charged by banks means the average predominant prime rate quoted by commercial banks to large business, as determined by the Board of Governors of the Federal Reserve System.

SOURCE: GC § 19515, as amended by P.L. 13-082 and R/R by P.L. 18-
015:X:39.