Maryland Code, Tax-General § 7-220

(b)(1) If the tax rate applicable to the person invading the corpus exceeds the tax rate already paid on the property, additional inheritance tax shall be due on the property withdrawn.

(2) The amount of additional inheritance tax due under paragraph (1) of this subsection is the difference between the inheritance tax that was paid on the property and the inheritance tax that would have been due on the property if determined at the higher rate.