Indiana Code Title 6. Taxation § 6-4.1-9-1

Sec. 1. (a) Except as otherwise provided in IC 6-4.1-6-6(b), the inheritance tax imposed as a result of a decedent's death is due twelve (12) months after the person's date of death.  If a person liable for payment of inheritance tax does not pay the tax on or before the due date, the person shall, except as provided in subsection (b), pay interest on the delinquent portion of the tax at the rate of ten percent (10%) per year from the date of the decedent's death to the date payment is made.

(b) If an unavoidable delay, such as necessary litigation, prevents a determination of the amount of inheritance tax due, the department of state revenue may reduce the rate of interest imposed under this section, for the time period beginning on the date of the decedent's death and ending when the cause of delay is removed, to six percent (6%) per year.