Del. Code tit. 5 § 964
If the agreement governing, or the bond, note or other evidence of, the loan so provides, the periodic percentage rate or rates of interest charged and collected in respect of the loan may, if the interest is not precomputed and taken in advance, vary in accordance with a schedule or formula. Such periodic percentage rate or rates may vary from time to time as the rate determined in accordance with such schedule or formula varies and such periodic percentage rate or rates, as so varied, may be made applicable to all or any part of outstanding unpaid amounts of such loan on and after the effective date of such variation. This section shall not be construed to limit the authority of a bank to charge and collect interest in respect of a loan in the manner and at the rate or rates authorized in any other section of this subchapter. Without limitation, a permissible schedule or formula hereunder may include provision in the agreement governing the loan for a change in the periodic percentage rate or rates of interest applicable to all or any part of outstanding unpaid amounts, whether by variation of the then applicable periodic percentage rate or rates of interest, variation of an index or margin or otherwise, contingent upon the happening of any event or circumstance specified in the loan agreement, which event or circumstance may include the failure of the borrower to perform in accordance with the terms of the loan agreement.
5 Del. C. § 964