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
(1)(A)#
the amount of the taxable estate, and
(1)(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 December 31, 1976 , if the modifications described in subsection (g) had been applicable at the time of such gifts.
For purposes of paragraph (1)(B), the term “adjusted taxable gifts” means the total amount of the taxable gifts (within the meaning of section 2503) made by the decedent after December 31, 1976 , other than gifts which are includible in the gross estate of the decedent.