For purposes of paragraph (1), the amount of gift tax paid with respect to any gift is an amount which bears the same ratio to the amount of gift tax paid under chapter 12 with respect to all gifts made by the donor for the calendar year (or preceding calendar period) in which such gift is made as the amount of such gift bears to the taxable gifts (as defined in section
2503
(a) but computed without the deduction allowed by section
2521) made by the donor during such calendar year or period. For purposes of the preceding sentence, the amount of any gift shall be the amount included with respect to such gift in determining (for the purposes of section
2503
(a)) the total amount of gifts made during the calendar year or period, reduced by the amount of any deduction allowed with respect to such gift under section
2522 (relating to charitable deduction) or under section
2523 (relating to marital deduction).