Background 

During the Medicare Open Enrollment Period, which runs from October 15 to December 7, Medicare beneficiaries can choose their Part D or Medicare Advantage (MA) plans. Medicare beneficiaries decide whether to enroll in fee-for-service (FFS) with a standalone Prescription Drug Plan (PDP) or in an MA plan. Enrollment decisions take effect at the start of the plan year on January 1.  

There are several types of PDP and MA plan options. Although some MA plans only cover Part A and B benefits, most MA plans include drug coverage. These plans are known as Medicare Advantage Prescription Drug Plans (MA-PDs). While many plans allow general enrollment by all Medicare beneficiaries, some limit coverage to specific types of beneficiaries. For example, MA-PD Special Needs Plans (SNPs) limit enrollment to beneficiaries with certain chronic conditions (C-SNPs), those who are dually eligible for both Medicare and Medicaid (D-SNPs), or beneficiaries who need long-term or other institutional care (I-SNPs). Other PDP and MA plans, known as Employer Group Waiver Plans (EGWPs), are offered to retirees by certain employers or associations.    

In late February, the Centers for Medicare and Medicaid Services (CMS) released the February 2025 MA and Part D Enrollment data. These data provide insight into enrollment decisions by beneficiaries in 2025 and indicate how MA and Part D enrollment is shifting in the first year of Part D benefit redesign implementation under the Inflation Reduction Act (IRA). 

Part D Enrollment by Plan Type 

The share of enrollees in both PDPs and MA-PDs has remained relatively stable from 2024 (Figure 1).  

Figure 1. Part D Enrollment by Plan Type, in Millions, 2021–2025 

From 2024 to 2025, enrollment in PDPs grew by 1.5% and enrollment in MA-PDs grew by about 4% (Figure 2). While PDP enrollment continues to reflect a trend of slower growth in recent years, the MA-PD enrollment growth in 2025 was more moderate compared to previous years (7% from 2023 to 2024 and over 9% from 2021 to 2022 and 2022 to 2023).  

Total enrollment in Medicare, encompassing both FFS and MA, has been steadily increasing at roughly 2% annually since 2020 according to the 2024 Medicare Trustees’ Report. While MA-PD enrollment slowed considerably in 2025, MA-PD enrollment continues to outpace the growth in overall Medicare enrollment.  

Figure 2. Annual Change in MA-PD and PDP Enrollment, 2022–2025 

Enrollment in PDPs varies by geography (Figure 3). Rural states continue to have a higher proportion of enrollment in PDPs, potentially due to provider networking constraints that impact MA-PD availability. PDPs are also more prevalent in areas where there is a significant population of retirees who receive medical coverage through programs such as Federal Employee Health Benefits. 

Figure 3. Proportion PDP Enrollment by State, as a Percentage of Total Part D Enrollment, 2025 

Part D Enrollment by Plan Sponsor 

Part D enrollment continues to be concentrated among national health plans. In 2025, 73% of Part D enrollment is in one of the five largest Part D plans. Among these plans, Centene had the largest increase in enrollment, growing by 19% across both PDP and MA-PD, while CVS had the largest decrease in enrollment, declining by 9% across both PDP and MA-PD. 

Medicare Advantage Enrollment by Plan Type 

In 2025, 62% of MA enrollees are in a general enrollment MA plan, 21% are in a SNP, and 17% are in an EGWP. While enrollment in general and employer MA plans grew modestly from 2024 to 2025 (by 1% and 3%, respectively), enrollment in SNPs continues to grow by double digits, fueled primarily by growth in C-SNP enrollment. Enrollment in C-SNPs grew by 67% from 2024 to 2025. C-SNPs now comprise 15% of all SNP enrollees, a five percentage point increase from 2024 (Figure 4). C-SNP offerings increased by 22% from 2024 to 2025. This broader availability of C-SNPs offerings may have influenced enrollment.  

Figure 4. Enrollment by SNP Type, 2021-2025 

Medicare Advantage Enrollment by Parent Organization 

Enrollment in MA is concentrated among several national health plans. In 2025, 70% of MA enrollment is in one of the five largest MA plans. Among these plans, Elevance had the largest increase in enrollment, growing by 14% across all MA plan types (including MA-PDs), while Humana had the largest decrease in enrollment, declining by 4% across all MA plan types. 

Enrollment Shifts Under the IRA 

In the first year of IRA implementation, enrollment shifts from PDPs into MA-PDs were moderate, despite a 26% reduction in the number of PDPs offered in 2025 relative to 2024. While many factors influence beneficiary enrollment decisions, the Part D premium stabilization demonstration, which limited enrollee PDP monthly premium increases to no more than $35, may have contributed to more moderate enrollment shifts into MA-PDs. 

To learn more about how MA and Part D enrollment shifts under the IRA may impact your organization, connect with us.  

Methodology 

Avalere used MA and Part D enrollment data released in February 2025 by CMS to conduct this analysis. The analysis includes territories and employer plans.