Del. Code tit. 5, § 2216

A licensee may charge and collect interest under a revolving credit plan on outstanding unpaid indebtedness in the borrower’s account under the plan at such daily, weekly, monthly, annual or other periodic percentage rate or rates as the agreement governing the plan provides or as established in the manner provided in the agreement governing the plan. Periodic interest may be calculated using an average daily balance, 2-cycle average daily balance, adjusted balance or previous balance method or using any other balance computation method provided for in the agreement governing the plan. Periodic billing cycles may be established in such manner and shall have such duration as may be specified in the agreement governing the plan.