42 CFR §457.611

The amount of a final allotment for a fiscal year after FY 2008, as determined under § 457.609 and reduced to reflect certain Medicaid expenditures in accordance with § 457.616, remains available until expended for Federal payments based on expenditures claimed during a 2-year period of availability, beginning with the fiscal year of the final allotment and ending with the end of the succeeding fiscal year following the fiscal year.