Section 1.861-1 - Income from sources within the United States(a)Categories of income. Part I (section 861 and following), subchapter N, chapter 1 of the Code, and the regulations thereunder determine the sources of income for purposes of the income tax. These sections explicitly allocate certain important sources of income to the United States or to areas outside the United States, as the case may be; and, with respect to the remaining income (particularly that derived partly from sources within and partly from sources without the United States), authorize the Secretary or his delegate to determine the income derived from sources within the United States, either by rules of separate allocation or by processes or formulas of general apportionment. The statute provides for the following three categories of income:(1)Within the United States. The gross income from sources within the United States, consisting of the items of gross income specified in section 861(a) plus the items of gross income allocated or apportioned to such sources in accordance with section 863(a). See §§ 1.861-2 to 1.861-7 , inclusive, and § 1.863-1 . The taxable income from sources within the United States, in the case of such income, shall be determined by deducting therefrom, in accordance with sections 861(b) and 863(a), the expenses, losses, and other deductions properly apportioned or allocated thereto and a ratable part of any other expenses, losses, or deductions which cannot definitely be allocated to some item or class of gross income. See §§ 1.861-8 and 1.863-1 .(2)Without the United States. The gross income from sources without the United States, consisting of the items of gross income specified in section 862(a) plus the items of gross income allocated or apportioned to such sources in accordance with section 863(a). See §§ 1.862-1 and 1.863-1 . The taxable income from sources without the United States, in the case of such income, shall be determined by deducting therefrom, in accordance with sections 862(b) and 863(a), the expenses, losses, and other deductions properly apportioned or allocated thereto and a ratable part of any other expenses, losses, or deductions which cannot definitely be allocated to some item or class of gross income. See §§ 1.862-1 and 1.863-1 .(3)Partly within and partly without the United States. The gross income derived from sources partly within and partly without the United States, consisting of the items specified in section 863(b)(1), (2), and (3). The taxable income allocated or apportioned to sources within the United States, in the case of such income, shall be determined in accordance with section 863 (a) or (b). See §§ 1.863-2 to 1.863-5 , inclusive.(4)Exceptions. An owner of certain aircraft or vessels first leased on or before December 28, 1980, may elect to treat income in respect of these aircraft or vessels as income from sources within the United States for purposes of sections 861(a) and 862(a). See § 1.861-9 . An owner of certain aircraft, vessels, or spacecraft first leased after December 28, 1980, must treat income in respect of these craft as income from sources within the United States for purposes of sections 861(a) and 862(a). See § 1.861-9A .(b)Taxable income from sources within the United States. The taxable income from sources within the United States shall consist of the taxable income described in paragraph (a)(1) of this section plus the taxable income allocated or apportioned to such sources, as indicated in paragraph (a)(3) of this section.(c)Computation of income. If a taxpayer has gross income from sources within or without the United States, together with gross income derived partly from sources within and partly from sources without the United States, the amounts thereof, together with the expenses and investment applicable thereto, shall be segregated; and the taxable income from sources within the United States shall be separately computed therefrom.T.D. 6500, 25 FR 11910, Nov. 26, 1960, as amended by T.D. 7928, 48 FR 55845, Dec. 16, 1983