(a) When a grantor or another person is treated under subpart E (section 671 and following) as the owner of any portion of a trust, there are included in computing his tax liability those items of income, deduction, and credit against tax attributable to or included in that portion. For example:

(1) If a grantor or another person is treated as the owner of an entire trust (corpus as well as ordinary income), he takes into account in computing his income tax liability all items of income, deduction, and credit (including capital gains and losses) to which he would have been entitled had the trust not been in existence during the period he is treated as owner.

(2) If the portion treated as owned consists of specific trust property and its income, all items directly related to that property are attributable to the portion. Items directly related to trust property not included in the portion treated as owned by the grantor or other person are governed by the provisions of subparts A through D (section 641 and following), part I, subchapter J, chapter 1 of the Code. Items that relate both to the portion treated as owned by the grantor and to the balance of the trust must be apportioned in a manner that is reasonable in the light of all the circumstances of each case, including the terms of the governing instrument, local law, and the practice of the trustee if it is reasonable and consistent.

(3) If the portion of a trust treated as owned by a grantor or another person consists of an undivided fractional interest in the trust, or of an interest represented by a dollar amount, a pro rata share of each item of income, deduction, and credit is normally allocated to the portion. Thus, where the portion owned consists of an interest in or a right to an amount of corpus only, a fraction of each item (including items allocated to corpus, such as capital gains) is attributed to the portion. The numerator of this fraction is the amount which is subject to the control of the grantor or other person and the denominator is normally the fair market value of the trust corpus at the beginning of the taxable year in question. The share not treated as owned by the grantor or other person is governed by the provisions of subparts A through D. See the last three sentences of paragraph (c) of this section for the principles applicable if the portion treated as owned consists of an interest in part of the ordinary income in contrast to an interest in corpus alone.

(b) If a grantor or another person is treated as the owner of a portion of a trust, that portion may or may not include both ordinary income and other income allocable to corpus. For example:

(1) Only ordinary income is included by reason of an interest in or a power over ordinary income alone. Thus, if a grantor is treated under section 673 as an owner by reason of a reversionary interest in ordinary income only, items of income allocable to corpus will not be included in the portion he is treated as owning. Similarly, if a grantor or another person is treated under sections 674-678 as an owner of a portion by reason of a power over ordinary income only, items of income allocable to corpus are not included in that portion. (See paragraph (c) of this section to determine the treatment of deductions and credits when only ordinary income is included in the portion.)

(2) Only income allocable to corpus is included by reason of an interest in or a power over corpus alone, if satisfaction of the interest or an exercise of the power will not result in an interest in or the exercise of a power over ordinary income which would itself cause that income to be included. For example, if a grantor has a reversionary interest in a trust which is not such as to require that he be treated as an owner under section 673, he may nevertheless be treated as an owner under section 677(a)(2) since any income allocable to corpus is accumulated for future distribution to him, but items of income included in determining ordinary income are not included in the portion he is treated as owning. Similarly, he may have a power over corpus which is such that he is treated as an owner under section 674 or 676 (a), but ordinary income will not be included in the portion he owns, if his power can only affect income received after a period of time such that he would not be treated as an owner of the income if the power were a reversionary interest. (See paragraph (c) of this section to determine the treatment of deductions and credits when only income allocated to corpus is included in the portion.)

(3) Both ordinary income and other income allocable to corpus are included by reason of an interest in or a power over both ordinary income and corpus, or an interest in or a power over corpus alone which does not come within the provisions of subparagraph (2) of this paragraph. For example, if a grantor is treated under section 673 as the owner of a portion of a trust by reason of a reversionary interest in corpus, both ordinary income and other income allocable to corpus are included in the portion. Further, a grantor includes both ordinary income and other income allocable to corpus in the portion he is treated as owning if he is treated under section 674 or 676 as an owner because of a power over corpus which can affect income received within a period such that he would be treated as an owner under section 673 if the power were a reversionary interest. Similarly, a grantor or another person includes both ordinary income and other income allocable to corpus in the portion he is treated as owning if he is treated as an owner under section 675 or 678 because of a power over corpus.

(c) If only income allocable to corpus is included in computing a grantor's tax liability, he will take into account in that computation only those items of income, deductions, and credit which would not be included under subparts A through D in the computation of the tax liability of the current income beneficiaries if all distributable net income had actually been distributed to those beneficiaries. On the other hand, if the grantor or another person is treated as an owner solely because of his interest in or power over ordinary income alone, he will take into account in computing his tax liability those items which would be included in computing the tax liability of a current income beneficiary, including expenses allocable to corpus which enter into the computation of distributable net income. If the grantor or other person is treated as an owner because of his power over or right to a dollar amount of ordinary income, he will first take into account a portion of those items of income and expense entering into the computation of ordinary income under the trust instrument or local law sufficient to produce income of the dollar amount required. There will then be attributable to him a pro rata portion of other items entering into the computation of distributable net income under subparts A through D, such as expenses allocable to corpus, and a pro rata portion of credits of the trust. For examples of computations under this paragraph, see paragraph (g) of § 1.677(a)-1.