(f) For the purposes of this subsection a delinquent tax consists of the balance of unpaid tax on January 1, 2018, including any accrued and unpaid interest the taxpayer owes on that date. An overpayment of tax consists of the balance of the tax overpaid on January 1, 2018, including any accrued interest owed to the taxpayer on that date. Except as otherwise provided in AS 43.55.020(g) and (h), and 15 AAC 55.830, the interest rate applicable to a delinquent tax or overpayment of a tax under this title, on or after January 1, 2018 is the interest rate under AS 43.05.225(1)(C) as of the first day of each calendar quarter in a calendar year calculated on an annualized basis by
(1) adding five and one-quarter percentage points to the annual rate charged by members banks for advances by the 12th Federal Reserve District as of the first day of each calendar quarter, compounded quarterly as of the last day of that quarter;(2) dividing the sum determined under (1) of this subsection by the total number of days in the calendar year; and(3) multiplying the quotient determined under (2) of this subsection by the total number of days in the quarter in which there is a delinquent tax or overpayment of tax.