(a) General rule. The applicability of the separate share rule provided by section 663(c) to estates and qualified revocable trusts within the meaning of section 645(b)(1) will generally depend upon whether the governing instrument and applicable local law create separate economic interests in one beneficiary or class of beneficiaries of such estate or trust. Ordinarily, a separate share exists if the economic interests of the beneficiary or class of beneficiaries neither affect nor are affected by the economic interests accruing to another beneficiary or class of beneficiaries. Separate shares include, for example, the income on bequeathed property if the recipient of the specific bequest is entitled to such income and a surviving spouse's elective share that under local law is entitled to income and appreciation or depreciation. Furthermore, a qualified revocable trust for which an election is made under section 645 is always a separate share of the estate and may itself contain two or more separate shares. Conversely, a gift or bequest of a specific sum of money or of property as defined in section 663(a)(1) is not a separate share.

(b) Special rule for certain types of beneficial interests. Notwithstanding the provisions of paragraph (a) of this section, a surviving spouse's elective share that under local law is determined as of the date of the decedent's death and is not entitled to income or any appreciation or depreciation is a separate share. Similarly, notwithstanding the provisions of paragraph (a) of this section, a pecuniary formula bequest that, under the terms of the governing instrument or applicable local law, is not entitled to income or to share in appreciation or depreciation constitutes a separate share if the governing instrument does not provide that it is to be paid or credited in more than three installments.

(c) Shares with multiple beneficiaries and beneficiaries of multiple shares. A share may be considered as separate even though more than one beneficiary has an interest in it. For example, two beneficiaries may have equal, disproportionate, or indeterminate interests in one share which is economically separate and independent from another share in which one or more beneficiaries have an interest. Moreover, the same person may be a beneficiary of more than one separate share.