26 U.S.C. § 2010: Unified credit against estate tax

A credit of the applicable credit amount shall be allowed to the estate of every decedent against the tax imposed by section 2001. The amount of the credit allowable under subsection (a) shall be reduced by an amount equal to 20 percent of the aggregate amount allowed as a specific exemption under section 2521 (as in effect before its repeal by the Tax Reform Act of 1976) with respect to gifts made by the decedent after September 8, 1976 . For purposes of this section, the applicable credit amount is the amount of the tentative tax which would be determined under section 2001(c) if the amount with respect to which such tentative tax is to be computed were equal to the applicable exclusion amount. the basic exclusion amount, and in the case of a surviving spouse, the deceased spousal unused exclusion amount. For purposes of this subsection, the basic exclusion amount is $15,000,000. such dollar amount, multiplied by the cost-of-living adjustment determined under section 1(f)(3) for such calendar year by substituting “calendar year 2025” for “calendar year 2016” in subparagraph (A)(ii) thereof. the basic exclusion amount, or the applicable exclusion amount of the last such deceased spouse of such surviving spouse, over the amount with respect to which the tentative tax is determined under section 2001(b)(1) on the estate of such deceased spouse. A deceased spousal unused exclusion amount may not be taken into account by a surviving spouse under paragraph (2) unless the executor of the estate of the deceased spouse files an estate tax return on which such amount is computed and makes an election on such return that such amount may be so taken into account. Such election, once made, shall be irrevocable. No election may be made under this subparagraph if such return is filed after the time prescribed by law (including extensions) for filing such return. Notwithstanding any period of limitation in section 6501, after the time has expired under section 6501 within which a tax may be assessed under chapter 11 or 12 with respect to a deceased spousal unused exclusion amount, the Secretary may examine a return of the deceased spouse to make determinations with respect to such amount for purposes of carrying out this subsection. The Secretary shall prescribe such regulations as may be necessary or appropriate to carry out this subsection. The amount of the credit allowed by subsection (a) shall not exceed the amount of the tax imposed by section 2001. Except as provided in paragraph (2), the amendments made by this section [amending this section and sections 2505, 2631, and 6018 of this title] shall apply to estates of decedents dying and gifts made after December 31, 2010 . The amendment made by subsection (b)(2) [amending section 2631 of this title ] shall apply to generation-skipping transfers after December 31, 2010 .” Except as provided in paragraphs (2) and (3), the amendments made by this section [amending this section and sections 2057, 2505, and 2631 of this title] shall apply to estates of decedents dying, and gifts made, after December 31, 2001 . The amendments made by subsection (b)(2) [amending section 2505 of this title ] shall apply to gifts made after December 31, 2009 . The amendments made by subsections (c) and (d) [amending sections 2057 and 2631 of this title] shall apply to estates of decedents dying, and generation-skipping transfers, after December 31, 2003 .”