39 CFR § 3060.10 - Costing.
(a) The assumed taxable income from competitive products for the Postal Service's theoretical competitive products enterprise for a fiscal year shall be based on total revenues generated by competitive products during that year less the costs identified in paragraph (b) of this section calculated using the methodology most recently approved by the Commission.
(b) The net income for the Postal Service's theoretical competitive products enterprise shall reflect the following costs:
(1) Attributable costs, including volume-variable costs, product-specific costs, and those inframarginal costs calculated as part of a competitive product's incremental costs; and
(2) The appropriate share of institutional costs assigned to competitive products by the Commission pursuant to 39 U.S.C. 3633(a)(3).