42 C.F.R. § 600.605
(a) General calculation. The Federal payment for an eligible individual in a given Federal fiscal year is the sum of the premium tax credit component, as described in paragraph (a)(1) of this section, and the cost-sharing reduction component, as described in paragraph (a)(2) of this section.
(b) Relevant factors in the payment methodology. In determining the premium tax credit and cost-sharing reduction components described in paragraph (a) of this section, the Secretary will consider the following factors to determine applicable adjustments: