26 CFR § 1.668(a)-1A - Amounts treated as received in prior taxable years; inclusion in gross income.
(a) Section 668(a) provides that the total of the amounts treated under sections 666 and 669 as having been distributed by the trust on the last day of a preceding taxable year of the trust shall be included in the income of the beneficiary or beneficiaries receiving them. The total of such amounts is includable in the income of each beneficiary to the extent the amounts would have been included under section 662 (a)(2) and (b) as if the total had actually been an amount properly paid by the trust under section 661 (a)(2) on the last day of such preceding taxable year. The total is included in the income of the beneficiary for the taxable year of the beneficiary in which such amounts are in fact paid, credited, or required to be distributed unless the taxable year of the beneficiary differs from the taxable year of the trust (see section 662(c) and the regulations thereunder). The character of the amounts treated as received by a beneficiary in prior taxable years, including taxes deemed distributed, in the hands of the beneficiary is determined by the rules set forth in section 662(b) and the regulations thereunder.
(b) Any deduction allowed to the trust in computing distributable net income for a preceding taxable year (such as depreciation, depletion, etc.) is not deemed allocable to a beneficiary because of amounts included in a beneficiary's gross income under this section since the deduction has already been utilized in reducing the amount included in the beneficiary's income.
(c) For purposes of applying section 668(a)(3), a trust shall be considered to be other than a “trust which is not required to distribute all of its income currently” for each taxable year prior to the first taxable year beginning after December 31, 1968, and ending after November 30, 1969, in which income is accumulated. Income will not be deemed to have been accumulated for purposes of applying section 668(a)(3) in a year if the trustee makes a determination, as evidenced by a statement on the return, to distribute all of the trust's income for such year and also makes a good faith determination as to the amount of such income and actually distributed for such year the entire amount so determined. The term “income,” as used in the preceding two sentences, is defined in §§ 1.643(b)-1 and 1.643(b)-2. Since, under such definitions, certain items may be included in distributable net income but are not, under applicable local law, “income” (as, for example, certain extraordinary dividends), a trust that has undistributed net income from such sources might still qualify as a trust that has not accumulated income. Also, for example, if a trust establishes a reserve for depreciation or depletion and applicable local law permits the deduction for such reserve in the computation of “income,” amounts so added to the reserve do not constitute an accumulation of income. If a trust has separate shares, and any share accumulates income, all shares of the trust will be considered to have accumulated income for purposes of section 668(a)(3). Amounts retained by a trust or a portion of a trust that is subject to subpart E (sections 671-678) shall not be considered accumulated income.