The contracting officer may negotiate expenditure-based or fixed-support award terms for either types of TIA subject to the requirements in this subpart. The fundamental difference between an expenditure-based and a fixed-support TIA is:

(a) For an expenditure-based TIA, the amounts of interim payments or the total amount ultimately paid to the recipient are based on the amounts the recipient expends on project costs. If a recipient completes the project specified at the time of award before it expends all of the agreed-upon Federal funding and recipient cost sharing, the Federal Government may recover its share of the unexpended balance of funds or, by mutual agreement with the recipient, amend the agreement to expand the scope of the RD&D project. An expenditure-based TIA, therefore, is analogous to a cost-type procurement contract or grant.

(b) For a fixed-support TIA, the amount of assistance is established at the time of award and is not meant to be adjusted later. In that sense, a fixed-support TIA is somewhat analogous to a fixed-price procurement contract.