42 CFR §430.20

1. (a)New plans. The effective date of a new plan—
   1. (1)May not be earlier than the first day of the quarter in which an approvable plan is submitted to the regional office; and
   2. (2)With respect to expenditures for medical assistance, may not be earlier than the first day on which the plan is in operation on a statewide basis.
2. (b)Plan amendment.
   1. (1)For a plan amendment that provides additional services to individuals eligible under the approved plan, increases the payment amounts for services already included in the plan, or makes additional groups eligible for services provided under the approved plan, the effective date is determined in accordance with paragraph (a) of this section.
   2. (2)For a plan amendment that changes the State's payment method and standards, the rules of § 447.256 of this chapter apply.
   3. (3)For other plan amendments, the effective date may be a date requested by the State if CMS approves it.