would be included in the estate of the taxpayer if the taxpayer died shall be treated as property of the taxpayer. (2) Inclusion of certain gifts Any property transferred by the taxpayer after the date of the enactment of this chapter, to an individual who is a member of the family of the taxpayer (as determined under section 267(c)(4)) and has not attained the age of 18 shall be treated as property of the taxpayer for any calendar year before the year in which such individual attains the age of 18. (d) Establishment of valuation rules Not later than 12 months after the date of the enactment of this section, the Secretary shall establish rules and methods for determining the value of any asset for purposes of this subtitle, including rules for the valuation of assets that are not publicly traded or that do not have a readily ascertainable value. Such rules and methods— (1) may utilize retrospective and prospective formulaic valuation methods not currently in use by the Secretary, (2) may require the use of formulaic valuation approaches for designated assets, including formulaic approaches based on proxies for determining presumptive valuations, formulaic approaches based on prospective adjustments from purchase prices or other prior events, or formulaic approaches based on retrospectively adding deferral charges based on eventual sale prices or other specified later events indicative of valuation, and (3) may address the use of valuation discounts. 2903. Special rules (a) Deceased individuals (1) In general In the case of any individual who dies during a calendar year and who is not married on the date of such individual's death— (A) section 2901 shall be applied by substituting the date of the applicable taxpayer's death for the last day of any calendar year , and (B) the amount of the tax imposed under such section shall be reduced by an amount which bears the same ratio to such amount (determined without regard to this subsection) as— (i) the number of days in the calendar year after the date of the