42 CFR § 417.442 - Risk HMO's and CMP's: Conditions for provision of additional benefits.
(a) General rule. Except as provided in paragraph (b) of this section, a risk HMO or CMP must, during any contract period, provide to its Medicare enrollees the additional benefits described in § 417.440(b)(4) if its ACRs (calculated in accordance with § 417.594) are less than the average per capita rates that CMS pays for the Medicare enrollees during the contract period.
(b) Exceptions -
(1) Reduced payment election. An HMO or CMP is not obligated to furnish additional services under paragraph (a) of this section if it has requested a reduction in its monthly payment from CMS under § 417.592(e), and it -
(ii) Elects to receive partially reduced payment and furnish Medicare enrollees with additional benefits described in § 417.440 (b)(4) so that the combined value of benefits and reduced payment is equivalent to the difference between the average of its per capita rates of payment and its ACR.
(2) Benefit stabilization fund. An HMO or CMP may elect to have a part of the value of the additional benefits it must provide under paragraph (a) of this section withheld in a benefit stabilization fund as described in § 417.596.