48 C.F.R. § 31.201-2 : Federal Acquisition Regulations System — FEDERAL ACQUISITION REGULATION — GENERAL CONTRACTING REQUIREMENTS — CONTRACT COST PRINCIPLES AND PROCEDURES — CONTRACTS WITH COMMERCIAL ORGANIZATIONS —2 - Determining allowability

(a) A cost is allowable only when the cost complies with all of the following requirements:
(1) Reasonableness.
(2) Allocability.
(3) Standards promulgated by the CAS Board, if applicable, otherwise, generally accepted accounting principles and practices appropriate to the circumstances.
(4) Terms of the contract.
(5) Any limitations set forth in this subpart.
(b) Certain cost principles in this subpart incorporate the measurement, assignment, and allocability rules of selected CAS and limit the allowability of costs to the amounts determined using the criteria in those selected standards. Only those CAS or portions of standards specifically made applicable by the cost principles in this subpart are mandatory unless the contract is CAS-covered (see 48 CFR 9903 ). Business units that are not otherwise subject to these standards under a CAS clause are subject to the selected standards only for the purpose of determining allowability of costs on Government contracts. Including the selected standards in the cost principles does not subject the business unit to any other CAS rules and regulations. The applicability of the CAS rules and regulations is determined by the CAS clause, if any, in the contract and the requirements of the standards themselves.
(c) When contractor accounting practices are inconsistent with this subpart 31.2, costs resulting from such inconsistent practices in excess of the amount that would have resulted from using practices consistent with this subpart are unallowable.
(d) A contractor is responsible for accounting for costs appropriately and for maintaining records, including supporting documentation, adequate to demonstrate that costs claimed have been incurred, are allocable to the contract, and comply with applicable cost principles in this subpart and agency supplements. The contracting officer may disallow all or part of a claimed cost that is inadequately supported.

48 C.F.R. §31.201-2

48 FR 42301, 9/19/1983, as amended at 57 FR 39590, 8/31/1992; 61 FR 31656, 6/20/1996; 69 FR 17767, 4/5/2004