12 USC 4306 - Payment of interest

(a) Calculated on full amount of principal 
Interest on an interest-bearing account at any depository institution shall be calculated by such institution on the full amount of principal in the account for each day of the stated calculation period at the rate or rates of interest disclosed pursuant to this chapter.
(b) No particular method of compounding interest required 
Subsection (a) of this section shall not be construed as prohibiting or requiring the use of any particular method of compounding or crediting of interest.
(c) Date by which interest must accrue 
Interest on accounts that are subject to this chapter shall begin to accrue not later than the business day specified for interest-bearing accounts in section 4005 of this title, subject to subsections (b) and (c) of such section.