26 U.S.C. § 2013: Credit for tax on prior transfers

80 percent, if within the third or fourth years preceding the decedent’s death; 60 percent, if within the fifth or sixth years preceding the decedent’s death; 40 percent, if within the seventh or eighth years preceding the decedent’s death; and 20 percent, if within the ninth or tenth years preceding the decedent’s death. Subject to the limitation prescribed in subsection (c), the credit provided by this section shall be an amount which bears the same ratio to the estate tax paid (adjusted as indicated hereinafter) with respect to the estate of the transferor as the value of the property transferred bears to the taxable estate of the transferor (determined for purposes of the estate tax) decreased by any death taxes paid with respect to such estate. For purposes of the preceding sentence, the estate tax paid shall be the Federal estate tax paid increased by any credits allowed against such estate tax under section 2012, or corresponding provisions of prior laws, on account of gift tax, and for any credits allowed against such estate tax under this section on account of prior transfers where the transferor acquired property from a person who died within 10 years before the death of the decedent. the estate tax imposed by section 2001 or section 2101 (after deducting the credits provided for in sections 2010, 2012, and 2014) computed without regard to this section, exceeds such tax computed by excluding from the decedent’s gross estate the value of such property transferred and, if applicable, by making the adjustment hereinafter indicated. If the credit provided in this section relates to property received from 2 or more transferors, the limitation provided in paragraph (1) of this subsection shall be computed by aggregating the value of the property so transferred to the decedent. The aggregate limitation so determined shall be apportioned in accordance with the value of the property transferred to the decedent by each transferor. there shall be taken into account the effect of the tax imposed by section 2001 or 2101, or any estate, succession, legacy, or inheritance tax, on the net value to the decedent of such property; where such property is encumbered in any manner, or where the decedent incurs any obligation imposed by the transferor with respect to such property, such encumbrance or obligation shall be taken into account in the same manner as if the amount of a gift to the decedent of such property was being determined; and if the decedent was the spouse of the transferor at the time of the transferor’s death, the net value of the property transferred to the decedent shall be reduced by the amount allowed under section 2056 (relating to marital deductions), as a deduction from the gross estate of the transferor. For purposes of this section, the term “property” includes any beneficial interest in property, including a general power of appointment (as defined in section 2041). the additional tax imposed by section 2032A(c) shall be treated as a Federal estate tax payable with respect to the estate of the transferor; and the value of such property and the amount of the taxable estate of the transferor shall be determined as if section 2032A did not apply with respect to such property.