Del. Code tit. 5 § 968
If the agreement governing a loan so provides, a bank may impose, as interest, a late or delinquency charge upon any outstanding unpaid installment payments or portions thereof under the loan agreement which are in default; provided, however, that in the case of a loan to an individual borrower, no such late or delinquency charge may be charged or imposed unless the agreement governing, or the bond, note or other evidence of, the loan so provides and that no more than 1 such late or delinquency charge may be imposed in respect of any single such installment payment or portion thereof regardless of the period during which it remains in default; and provided further, however, that for the purpose only of the preceding proviso all payments by the borrower shall be deemed to be applied to satisfaction of installment payments in the order in which they become due. Nothing contained in this section shall limit, restrict or otherwise affect the right of a bank under and pursuant to §§ 963 and 964 of this title to change the periodic percentage rate or rates of interest applicable to the loan agreement between the bank and a borrower upon the occurrence of a delinquency or default or other failure of the borrower to perform in accordance with the terms of the loan agreement.
5 Del. C. § 968