The difference between the amount of tax computed under subdivision (i) of this subparagraph for each year and the amount computed under subdivision (ii) of this subparagraph for that year is the additional tax resulting from the inclusion in gross income for that year of the amount determined under subparagraph (2) of this paragraph. If the number of preceding taxable years of the trust, on the last day of which an amount is deemed under section 666(a) to have been distributed, is less than three, the taxable years of the beneficiary for which this recomputation is made shall equal the number of years in which an amount is deemed under section 666(a) to have been distributed, commencing with the taxable year of the beneficiary in which the accumulation distribution is paid, credited, or required to be distributed to him. If the beneficiary was not alive during one of the two taxable years immediately preceding the taxable year, the tax resulting from the inclusion of the amount determined in subparagraph (2) of this paragraph in the gross income of the beneficiary will be computed only for the taxable year in which the accumulation distribution was paid, credited, or required to be distributed to him and the preceding year during which the beneficiary was alive. In the event the beneficiary was not alive during either of the 2 years immediately preceding the taxable year in which the accumulation distribution was paid, credited, or required to be distributed, the tax shall be computed on the basis of the beneficiary's taxable year without regard to the inclusion in income required by section 668(a) of any amount other than pursuant to section 669(a)(1)(B). For example, assume that a foreign trust created by a U.S. person accumulates $3,000 of income in 1964 and $7,000 in 1963 and then distributes the accumulated income on January 1, 1965, to a beneficiary who is a U.S. person. The limitation on tax is determined by recomputing the beneficiary's gross income for 1964 and 1965 by adding $5,000 to his gross income for each year. If the same distribution were made to an infant who was born in 1965, the limitation on tax would be computed by adding $5,000 to his gross income for such year. In the case of the infant, the resulting increase in tax would be multiplied by two to arrive at the limitation on the increase in his tax for 1965 attributable to such distribution.
26 C.F.R. §1.669(a)-4