26 CFR § 1.1402(a)-5 - Dividends and interest.
(b) Interest on any bond, debenture, note, or certificate, or other evidence of indebtedness, issued with interest coupons or in registered form by any corporation (including one issued by a government or political subdivision thereof) is excluded unless such interest is received in the course of a trade or business as a dealer in stocks or securities. However, interest with respect to which a credit against tax is allowable as provided in section 35, that is, interest on certain obligations of the United States and its instrumentalities, is not included in net earnings from self-employment even though received in the course of a trade or business as a dealer in stocks or securities. Only interest on bonds, debentures, notes, or certificates, or other evidence of indebtedness, issued with interest coupons or in registered form by a corporation, is excluded in the case of all persons other than dealers in stocks or securities; other interest received in the course of any trade or business (such as interest received by a pawnbroker on his loans or interest received by a merchant on his accounts or notes receivable) is not excluded.
(c) Dividends and interest of the character excludable under paragraphs (a) and (b) of this section received by an individual on stocks or securities held for speculation or investment are excluded whether or not the individual is a dealer in stocks or securities.
(d) A dealer in stocks or securities is a merchant of stocks or securities with an established place of business, regularly engaged in the business of purchasing stocks or securities and reselling them to customers; that is, he is one who as a merchant buys stocks or securities and sells them to customers with a view to the gains and profits that may be derived therefrom. Persons who buy and sell or hold stocks or securities for investment or speculation, irrespective of whether such buying or selling constitutes the carrying on of a trade or business, are not dealers in stocks or securities.