If the property was acquired by gift after December 31, 1920, the basis shall be the same as it would be in the hands of the donor or the last preceding owner by whom it was not acquired by gift, except that if such basis (adjusted for the period before the date of the gift as provided in section 1016) is greater than the fair market value of the property at the time of the gift, then for the purpose of determining loss the basis shall be such fair market value. If the facts necessary to determine the basis in the hands of the donor or the last preceding owner are unknown to the donee, the Secretary shall, if possible, obtain such facts from such donor or last preceding owner, or any other person cognizant thereof. If the Secretary finds it impossible to obtain such facts, the basis in the hands of such donor or last preceding owner shall be the fair market value of such property as found by the Secretary as of the date or approximate date at which, according to the best information that the Secretary is able to obtain, such property was acquired by such donor or last preceding owner.
If the property was acquired after December 31, 1920, by a transfer in trust (other than by a transfer in trust by a gift, bequest, or devise), the basis shall be the same as it would be in the hands of the grantor increased in the amount of gain or decreased in the amount of loss recognized to the grantor on such transfer under the law applicable to the year in which the transfer was made.
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).
For purposes of paragraph (1), where the donor and his spouse elected, under section 2513 to have the gift considered as made one-half by each, the amount of gift tax paid with respect to such gift under chapter 12 shall be the sum of the amounts of tax paid with respect to each half of such gift (computed in the manner provided in paragraph (2)).
For purposes of section 1016(b), an increase in basis under paragraph (1) shall be treated as an adjustment under section 1016(a).