72-16-909. When and where tax payable -- interest. (1) The estate tax is payable to the department of revenue.

(2) If the tax is not paid within 18 months of the death of the decedent, interest must be charged and collected at the rate of 10% a year from the time that the tax accrued, unless because of claims made upon the estate, necessary litigation, or other unavoidable cause of delay, the tax is not determined and paid on time. Interest at the rate of 6% must be charged upon the amount of tax due from the time of accrual until the cause of the delay is removed, and after that time, interest at the rate of 10% must be charged.

(3) Litigation to defeat the payment of the tax is not necessary litigation.

(4) When permission has been granted to defer payment of tax under 72-16-910, interest must be charged at the rate of 6% after 1 year from the date of death until the date of payment.