2 CFR § 200.403 - Factors affecting allowability of costs.
Except where otherwise authorized by statute, costs must meet the following general criteria in order to be allowable under Federal awards:
(a) Be necessary and reasonable for the performance of the Federal award and be allocable thereto under these principles.
(b) Conform to any limitations or exclusions set forth in these principles or in the Federal award as to types or amount of cost items.
(c) Be consistent with policies and procedures that apply uniformly to both federally-financed and other activities of the non-Federal entity.
(d) Be accorded consistent treatment. A cost may not be assigned to a Federal award as a direct cost if any other cost incurred for the same purpose in like circumstances has been allocated to the Federal award as an indirect cost.
(h) Cost must be incurred during the approved budget period. The Federal awarding agency is authorized, at its discretion, to waive prior written approvals to carry forward unobligated balances to subsequent budget periods pursuant to § 200.308(e)(3).