(a) Determination of taxable income. Section 863(b) provides an alternate method for determining taxable income from sources within the United States in the case of gross income derived from sources partly within and partly without the United States. Under this method, taxable income is determined by deducting from such gross income the expenses, losses, or other deductions properly apportioned or allocated thereto and a ratable part of any other expenses, losses, or deductions that cannot definitely be allocated to some item or class of gross income. The income to which this section applies will consist of gains, profits, and income:

(1) From certain transportation or other services rendered partly within and partly without the United States to the extent not within the scope of section 863(c) or other specific provisions of this title;

(2) From the sale of inventory property (within the meaning of section 865(i)) produced (in whole or in part) by the taxpayer in the United States and sold outside the United States or produced (in whole or in part) by the taxpayer outside the United States and sold in the United States; or

(3) Derived from the purchase of personal property within a possession of the United States and its sale within the United States, to the extent not excluded from the scope of these regulations under § 1.936-6(a)(5), Q&A 7.

(b) Determination of source of taxable income. Income treated as derived from sources partly within and partly without the United States under paragraph (a) of this section may be allocated or apportioned to sources within and without the United States pursuant to §§ 1.863-1, 1.863-3, 1.863-4, 1.863-8, and 1.863-9. To determine the source of certain types of income described in paragraph (a)(1) of this section, see § 1.863-4. To determine the source of gross income described in paragraph (a)(2) of this section, see § 1.863-1 for natural resources, § 1.863-3 for other sales of inventory property, and § 1.863-8 for source of gross income from space and ocean activity. Section 1.865-3 may apply instead of the provisions in this section to source gross income from sales of personal property (including inventory property) by nonresidents attributable to an office or other fixed place of business in the United States. To determine the source of income partly from sources within a possession of the United States, including income described in paragraph (a)(3) of this section, see § 1.863-3(e).

(c) Applicability date. Except as provided in this paragraph (c), this section applies to taxable years beginning after December 30, 1996. Paragraph (b) of this section applies to taxable years ending on or after December 23, 2019. However, a taxpayer may apply paragraph (b) of this section in its entirety for taxable years beginning after December 31, 2017, and ending before December 23, 2019, provided that the taxpayer and all persons related to the taxpayer (within the meaning of section 267 or 707) apply paragraph (b) of this section and §§ 1.863-1(b), 1.863-3, 1.863-8(b)(3)(ii), 1.864-5(a) and (b), 1.864-6(c)(2), and 1.865-3 in their entirety for the taxable year, and once applied, the taxpayer and all persons related to the taxpayer (within the meaning of section 267 or 707) continue to apply these regulations in their entirety for all subsequent taxable years. For regulations generally applicable to taxable years ending before December 23, 2019, see § 1.863-2 as contained in 26 CFR part 1 revised as of April 1, 2020.