12 CFR § 1030.7 - Payment of interest.
(a) Permissible methods—(1) Balance on which interest is calculated. Institutions shall calculate interest on the full amount of principal in an account for each day by use of either the daily balance method or the average daily balance method. Institutions shall calculate interest by use of a daily rate of at least 1/365 of the interest rate. In a leap year a daily rate of 1/366 of the interest rate may be used.
(2) Determination of minimum balance to earn interest. An institution shall use the same method to determine any minimum balance required to earn interest as it uses to determine the balance on which interest is calculated. An institution may use an additional method that is unequivocally beneficial to the consumer.
(b) Compounding and crediting policies. This section does not require institutions to compound or credit interest at any particular frequency.
(c) Date interest begins to accrue. Interest shall begin to accrue not later than the business day specified for interest-bearing accounts in section 606 of the Expedited Funds Availability Act (12 U.S.C. 4005) and in § 229.14 of that act's implementing Regulation CC (12 CFR part 229). Interest shall accrue until the day funds are withdrawn.