26 CFR § 1.652(b)-3 - Allocation of deductions.
(a) All deductible items directly attributable to one class of income (except dividends excluded under section 116) are allocated thereto. For example, repairs to, taxes on, and other expenses directly attributable to the maintenance of rental property or the collection of rental income are allocated to rental income. See § 1.642(e)-1 for treatment of depreciation of rental property. Similarly, all expenditures directly attributable to a business carried on by a trust are allocated to the income from such business. If the deductions directly attributable to a particular class of income exceed that income, the excess is applied against other classes of income in the manner provided in paragraph (d) of this section.
(b) The deductions which are not directly attributable to a specific class of income may be allocated to any item of income (including capital gains) included in computing distributable net income, but a portion must be allocated to nontaxable income (except dividends excluded under section 116) pursuant to section 265 and the regulations thereunder. For example, if the income of a trust is $30,000 (after direct expenses), consisting equally of $10,000 of dividends, tax-exempt interest, and rents, and income commissions amount to $3,000, one-third ($1,000) of such commissions should be allocated to tax-exempt interest, but the balance of $2,000 may be allocated to the rents or dividends in such proportions as the trustee may elect. The fact that the governing instrument or applicable local law treats certain items of deduction as attributable to corpus or to income not included in distributable net income does not affect allocation under this paragraph. For instance, if in the example set forth in this paragraph the trust also had capital gains which are allocable to corpus under the terms of the trust instrument, no part of the deductions would be allocable thereto since the capital gains are excluded from the computation of distributable net income under section 643(a)(3).
(c) Examples of expenses which are considered as not directly attributable to a specific class of income are trustee's commissions, the rental of safe deposit boxes, and State income and personal property taxes.
(d) To the extent that any items of deduction which are directly attributable to a class of income exceed that class of income, they may be allocated to any other class of income (including capital gains) included in distributable net income in the manner provided in paragraph (b) of this section, except that any excess deductions attributable to tax-exempt income (other than dividends excluded under section 116) may not be offset against any other class of income. See section 265 and the regulations thereunder. Thus, if the trust has rents, taxable interest, dividends, and tax-exempt interest, and the deductions directly attributable to the rents exceed the rental income, the excess may be allocated to the taxable interest or dividends in such proportions as the fiduciary may elect. However, if the excess deductions are attributable to the tax-exempt interest, they may not be allocated to either the rents, taxable interest, or dividends.