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4 individuals, PACE programs under section 1894, any “fallback” prescription drug plans, and plans established through reasonable cost reimbursement contracts under section 1876(h) of the Act (“Cost Plans”). The reference month for the CY 2026 calculation was June 2025. The national average monthly bid amount for CY 2026 is $239.27.

Part D Base Beneficiary Premium Section 1860D-13(a) of the Act, as amended by section 11201 of the Inflation Reduction Act of 2022 (IRA), specifies the methodology for calculating the base beneficiary premium (BBP). Specifically, the BBP for 2024 through 2029 is equal to the lesser of the following calculations:

A. The prior year’s BBP increased by 6 percent.

B. The product of the beneficiary premium percentage and the national average monthly bid amount. The beneficiary premium percentage (“applicable percentage”) is a fraction, with a numerator of 25.5 percent and a denominator equal to 100 percent minus a percentage equal to (i) the total reinsurance payments that CMS estimates will be paid for the coverage year, divided by (ii) that amount plus the total payments that CMS estimates will be paid to Part D plans based on the standardized bid amount during the year, taking into account amounts paid by both CMS and plan enrollees.

The result of calculation A is $38.99. 2025 BBP x 1.06 or $36.78 x 1.06 = $38.99 The result of calculation B is $75.38. Therefore, the Part D BBP for CY 2025 is $38.99.0F1 In accordance with section 1860D-13(a) of the Act, codified in 42 CFR § 423.286, Part D beneficiary premiums are calculated as the BBP adjusted by the following factors: (i) the difference between the plan’s standardized bid amount and the national average monthly bid amount; (ii) adjusted by any supplemental premium; (iii) an increase for any late enrollment penalty; (iv) a decrease for MA-PDs that apply MA A/B rebates to buy down the Part D premium; and (v) elimination or decrease with the application of the low-income premium subsidy.

Part D Regional Low-Income Premium Subsidy Amounts In accordance with 42 CFR § 423.780, low-income subsidy (LIS) individuals are entitled to a premium subsidy equal to 100 percent of the premium subsidy amount. A Part D plan’s premium subsidy amount is the lesser of the plan’s premium for basic coverage or the regional low-income

1 As noted above, the actual Part D premiums paid by individual beneficiaries equal the BBP adjusted by several factors. In practice, premiums vary significantly from one Part D plan to another and seldom equal the base beneficiary premium.