General rules
(a) Except as otherwise provided in sections 3103–3109 of this title, all appropriations or funds available for obligation for a definite period of time shall be so apportioned as to prevent obligation or expenditure thereof in a manner which would indicate a necessity for deficiency or supplemental appropriations for such period; and all appropriations or funds not limited to a definite period of time, and all authorizations to create obligations by contract in advance of appropriations, shall be so apportioned as to achieve the most effective and economical use thereof. As used in sections 3103–3109 of this title, the term “appropriation” means appropriations, funds and authorizations to create obligations by contract in advance of appropriations.
Reserves
(b) In apportioning any appropriations, reserves may be established to provide for contingencies, or to effect savings whenever savings are made possible by or through changes in requirements, greater efficiency of operations, or other developments subsequent to the date on which such appropriation was made available. Whenever it is determined by an officer designated in section 3104 of this title to make apportionments and reapportionments that any amount so reserved will not be required to carry out the purposes of the appropriation concerned, he shall recommend the rescission of such amount in the usual manner for submitting requests with respect to appropriations.
Distribution
(c) Any appropriation subject to apportionment shall be distributed by months, calendar quarters, operating seasons, or other time periods, or by activities, functions, projects, or objects, or by a combination thereof, as may be deemed appropriate by the officer designated in section 3104 of this title to make apportionments and reapportionments. Except as otherwise specified by the officer making the apportionment, amounts so apportioned shall remain available for obligation, in accordance with the terms of the appropriation, on a cumulative basis unless reapportioned.
Review
(d) Apportionments shall be reviewed at least four times each year by the officer designated in section 3104 of this title to make apportionments and reapportionments, and such reapportionments made or such reserves established, modified, or released as may be necessary to further the effective use of the appropriation concerned, in accordance with the purposes stated in subsection (a) of this section.