34 C.F.R. § 681.13 – Interest.

(a) Rate. At the lender's option, the interest rate on the HEAL loan may be calculated on a fixed rate or on a variable rate basis. However, whichever method is selected must continue over the life of the loan, except where the loan is consolidated with another HEAL loan.
1. (1) For all loans made on or after October 22, 1985, for each calendar quarter, the Secretary determines the maximum annual HEAL interest rate by determining the average of the bond equivalent rates reported for the 91-day U.S. Treasury bills auctioned for the preceding calendar quarter, adding 3 percentage points, and rounding that amount to the next higher one-eighth of 1 percent.
2. (2) Interest that is calculated on a fixed rate basis is determined for the life of the loan during the calendar quarter in which the loan is executed. It may not exceed the rate determined for that quarter by the Secretary under paragraph (a)(1) of this section.
3. (3) Interest that is calculated on a variable rate basis varies every calendar quarter throughout the life of the loan as the market price of U.S. Treasury bills changes. For any quarter it may not exceed the rate determined by the Secretary under paragraph (a)(1) of this section.
4. (4) The Secretary announces the rate determined under paragraph (a)(1) of this section on a quarterly basis through a notice published on the Department's student aid Web site at www.ifap.ed.gov.
(b) Compounding of interest. Interest accrues from the date the loan is disbursed until the loan is paid in full. Unpaid accrued interest shall be compounded not more frequently than semiannually and added to principal. However, a lender or holder may postpone the compounding of interest before the beginning of the repayment period or during periods of deferment or forbearance and add interest to principal at the time repayment of principal begins or resumes.
(c) Payment. Repayment of principal and interest is due when the repayment period begins. A lender or holder must permit a borrower to postpone paying interest before the beginning of the repayment period or during a period of deferment or forbearance. In these cases, payment of interest begins or resumes on the date repayment of principal begins or resumes.
(d) Usury laws. No provision of any Federal or State law that limits the rate or amount of interest payable on loans shall apply to a HEAL loan.