(a) Nondeductibility of expenses allocable to exempt income.

(1) No amount shall be allowed as a deduction under any provision of the Code for any expense or amount which is otherwise allowable as a deduction and which is allocable to a class or classes of exempt income other than a class or classes of exempt interest income.

(2) No amount shall be allowed as a deduction under section 212 (relating to expenses for production of income) for any expense or amount which is otherwise allowable as a deduction and which is allocable to a class or classes of exempt interest income.

(b) Exempt income and nonexempt income.

(1) As used in this section, the term class of exempt income means any class of income (whether or not any amount of income of such class is received or accrued) wholly exempt from the taxes imposed by Subtitle A of the Code. For purposes of this section, a class of income which is considered as wholly exempt from the taxes imposed by subtitle A includes any class of income which is:

(i) Wholly excluded from gross income under any provision of Subtitle A, or

(ii) Wholly exempt from the taxes imposed by Subtitle A under the provisions of any other law.

(2) As used in this section the term nonexempt income means any income which is required to be included in gross income.

(c) Allocation of expenses to a class or classes of exempt income. Expenses and amounts otherwise allowable which are directly allocable to any class or classes of exempt income shall be allocated thereto; and expenses and amounts directly allocable to any class or classes of nonexempt income shall be allocated thereto. If an expense or amount otherwise allowable is indirectly allocable to both a class of nonexempt income and a class of exempt income, a reasonable proportion thereof determined in the light of all the facts and circumstances in each case shall be allocated to each.

(d) Statement of classes of exempt income; records.

(1) A taxpayer receiving any class of exempt income or holding any property or engaging in any activity the income from which is exempt shall submit with his return as a part thereof an itemized statement, in detail, showing (i) the amount of each class of exempt income, and (ii) the amount of expenses and amounts otherwise allowable allocated to each such class (the amount allocated by apportionment being shown separately) as required by paragraph (c) of this section. If an item is apportioned between a class of exempt income and a class of nonexempt income, the statement shall show the basis of the apportionment. Such statement shall also recite that each deduction claimed in the return is not in any way attributable to a class of exempt income.

(2) The taxpayer shall keep such records as will enable him to make the allocations required by this section. See section 6001 and the regulations thereunder.