((a)) ** Imposition** A tax is hereby imposed on the transfer of the taxable estate of every decedent who is a citizen or resident of the United States.

((b)) ** Computation of tax** The tax imposed by this section shall be the amount equal to the excess (if any) of—

((1)) a tentative tax computed under subsection (c) on the sum of—

((A)) the amount of the taxable estate, and

((B)) the amount of the adjusted taxable gifts, over

((2)) the aggregate amount of tax which would have been payable under chapter 12 with respect to gifts made by the decedent after , if the modifications described in subsection (g) had been applicable at the time of such gifts.

((c)) ** Rate schedule**

((d)) ** Adjustment for gift tax paid by spouse** For purposes of subsection (b)(2), if—

((1)) the decedent was the donor of any gift one-half of which was considered under section 2513 as made by the decedent’s spouse, and

((2)) the amount of such gift is includible in the gross estate of the decedent,

((e)) ** Coordination of sections 2513 and 2035** If—

((1)) the decedent’s spouse was the donor of any gift one-half of which was considered under section 2513 as made by the decedent, and

((2)) the amount of such gift is includible in the gross estate of the decedent’s spouse by reason of section 2035,

((f)) ** Valuation of gifts**

((1)) ** In general** If the time has expired under section 6501 within which a tax may be assessed under chapter 12 (or under corresponding provisions of prior laws) on—

((A)) the transfer of property by gift made during a preceding calendar period (as defined in section 2502(b)); or

((B)) an increase in taxable gifts required under section 2701(d),

((2)) ** Final determination** For purposes of paragraph (1), a value shall be treated as finally determined for purposes of chapter 12 if—

((A)) the value is shown on a return under such chapter and such value is not contested by the Secretary before the expiration of the time referred to in paragraph (1) with respect to such return;

((B)) in a case not described in subparagraph (A), the value is specified by the Secretary and such value is not timely contested by the taxpayer; or

((C)) the value is determined by a court or pursuant to a settlement agreement with the Secretary.

((g)) ** Modifications to tax payable**

((1)) ** Modifications to gift tax payable to reflect different tax rates** For purposes of applying subsection (b)(2) with respect to 1 or more gifts, the rates of tax under subsection (c) in effect at the decedent’s death shall, in lieu of the rates of tax in effect at the time of such gifts, be used both to compute—

((A)) the tax imposed by chapter 12 with respect to such gifts, and

((B)) the credit allowed against such tax under section 2505, including in computing—

((i)) the applicable credit amount under section 2505(a)(1), and

((ii)) the sum of the amounts allowed as a credit for all preceding periods under section 2505(a)(2).

((2)) ** Modifications to estate tax payable to reflect different basic exclusion amounts** The Secretary shall prescribe such regulations as may be necessary or appropriate to carry out this section with respect to any difference between—

((A)) the basic exclusion amount under section 2010(c)(3) applicable at the time of the decedent’s death, and

((B)) the basic exclusion amount under such section applicable with respect to any gifts made by the decedent.