Medicare Advantage Markets Remain Highly Concentrated, Limiting Competition Despite Enrollment Growth

Nearly all Medicare Advantage (MA) markets across the US were classified as highly or very highly concentrated in 2024, raising questions about the competitive dynamics of this rapidly growing insurance sector. A new analysis found that 79% of counties were highly concentrated, and another 18% were very highly concentrated. Less than 1% of counties were moderately concentrated, and none were considered unconcentrated.

Despite an increase in the number of available plans and insurers since 2018, most Medicare Advantage enrollees—89%—reside in highly concentrated markets, with another 4% in very highly concentrated areas. This suggests that the apparent variety in plan options may not reflect true competition at the local level.

The analysis found that many of the most rural counties were the most concentrated, with 39% of the most rural areas classified as very highly concentrated, compared to 6% of urban counties. In total, 90% of all Medicare beneficiaries lived in a county where at least half of MA enrollees were in plans offered by just one or two insurers.

UnitedHealthcare and Humana held a dominant share of the MA market in 2024, comprising 41% and 25% of total enrollment, respectively. In 44% of all counties, a single insurer held more than 50% enrollment. UnitedHealthcare was the single insurer with at least 50% enrollment in 22% of counties, including major markets such as Dallas County, TX (55%) and Milwaukee County, WI (64%).

The analysis underscores a persistent concentration of power among a few large insurers, with implications for beneficiary choice and plan competition. The authors note that while plan availability has increased, “the growth in enrollment and plan availability has not occurred in the context of a competitive market.”

Reference 
Zhu N, Biniek JF, Sroczynski N, Neuman T. Most Medicare Advantage markets are dominated by one or two insurers. KFF. Published July 14, 2025. Accessed August 4, 2025. https://www.kff.org/medicare/issue-brief/most-medicare-advantage-markets-are-dominated-by-one-or-two-insurers/