26 C.F.R. § 20.2015-1
The allowance of credit, however, is subject to the other limitations contained in sections 2011 and 2014 and, in the case of the estate of a decedent who was a nonresident not a citizen of the United States, in section 2102(b).
Example (1). One-third of the Federal estate tax was attributable to a remainder interest in real property located in State Y, and two-thirds of the Federal estate tax was attributable to other property located in State X. The payment of the tax attributable to the remainder interest was postponed under the provisions of section 6163(a). The maximum credit allowable for State death taxes under the provisions of section 2011 is $12,000. Therefore, of the maximum credit allowable, $4,000 is attributable to the remainder interest and $8,000 is attributable to the other property. Within the 4-year period provided for in section 2011, inheritance tax in the amount of $9,000 was paid to State X in connection with the other property. With respect to this $9,000, $8,000 (the maximum amount allowable) is allowed as a credit against the Federal estate tax attributable to the other property, and $1,000 is allowed as a credit against the postponed tax. The life estate or other precedent interest expired after July 4, 1958. After the expiration of the 4-year period but before the expiration of the period of postponment elected under section 6163(a) and of the period of extension granted under section 6163(b) for payment of the tax, inheritance tax in the amount of $5,000 was paid to State Y in connection with the remainder interest. As the maximum credit allowable with respect to the remainder interest is $4,000 and $1,000 has already been allowed as a credit, an additional $3,000 will be credited against the Federal estate tax attributable to the remainder interest. It should be noted that if the life estate or other precedent interest had expired after the expiration of the 4-year period but before July 5, 1958, the same result would be reached only if the inheritance tax had been paid to State Y before the expiration of 60 days after the termination of the life estate or other precedent interest.
Example (2). The facts are the same as in example (1), except that within the 4-year period inheritance tax in the amount of $2,500 was paid to State Y with respect to the remainder interest and inheritance tax in the amount of $7,500 was paid to State X with respect to the other property. The amount of $8,000 is allowed as a credit against the Federal estate tax attributable to the other property and the amount of $2,000 is allowed as a credit against the postponed tax. The life estate or other precedent interest expired after July 4, 1958. After the expiration of the 4-year period but before the expiration of the period of postponement elected under section 6163(a) and of the period of extension granted under section 6163(b) for payment of the tax, inheritance tax in the amount of $5,000 was paid to State Y in connection with the remainder interest. As the maximum credit allowable with respect to the remainder interest is $4,000 and $2,000 already has been allowed as a credit, an additional $2,000 will be credited against the Federal estate tax attributable to the remainder interest. It should be noted that if the life estate or other precedent interest had expired after the expiration of the 4-year period but before July 5, 1958, the same result would be reached only if the inheritance tax had been paid to State Y before the expiration of 60 days after the termination of the life estate or other precedent interest.
Example (3). The facts are the same as in example (2), except that no payment was made to State Y within the 4-year period. The amount of $7,500 is allowed as a credit against the Federal estate tax attributable to the other property. After termination of the life interest additional credit will be allowed in the amount of $4,000 against the Federal estate tax attributable to the remainder interest. Since the payment of $5,000 was made to State Y following the expiration of the 4-year period, no part of the payment may be allowed as a credit against the Federal estate tax attributable to the other property.
26 C.F.R. §20.2015-1