48 CFR § 9905.506-40 - Fundamental requirement.
(2) An annual period other than the fiscal year may, as provided in 9905.506-50(d), be used as the cost accounting period if its use is an established practice of the institution.
(3) A transitional cost accounting period other than a year shall be used whenever a change of fiscal year occurs.
(b) An institution shall follow consistent practices in the selection of the cost accounting period or periods in which any types of expense and any types of adjustment to expense (including prior-period adjustments) are accumulated and allocated.
(c) The same cost accounting period shall be used for accumulating costs in an indirect cost pool as for establishing its allocation base, except that the contracting parties may agree to use a different period for establishing an allocation base as provided in 9905.506-50(e).