42 C.F.R. § 57.1508
The length of time for which interest subsidy payments will be made under the agreement, the amount of loan with respect to which such payments will be made, and the level of such payments shall be determined by the Secretary on the basis of the availability of funds and his determination of the applicant's need therefor taking into consideration his analysis of the present and reasonable projected future financial ability of the applicant to repay the principal and interest of the loan without jeopardizing the quality of its educational program: Provided however, That each such interest subsidy payment shall not exceed the amount necessary to reduce by 3 percent per annum the net effective interest rate otherwise payable on the loan or the portion thereof with respect to which such interest subsidy is paid.
42 C.F.R. §57.1508