2 CFR § 200.504 - Frequency of audits.
Except for the provisions for biennial audits provided in paragraphs (a) and (b) of this section, audits required by this part must be performed annually. Any biennial audit must cover both years within the biennial period.
(a) A state, local government, or Indian tribe that is required by constitution or statute, in effect on January 1, 1987, to undergo its audits less frequently than annually, is permitted to undergo its audits pursuant to this part biennially. This requirement must still be in effect for the biennial period.
(b) Any nonprofit organization that had biennial audits for all biennial periods ending between July 1, 1992, and January 1, 1995, is permitted to undergo its audits pursuant to this part biennially.