Medicare Advantage markets highly concentrated, KFF finds

Medicare Advantage markets are very concentrated across the U.S., with 79% of counties considered “high concentrated” and 18% considered “very highly concentrated” in a new analysis from KFF.

Fewer than 1% were moderately concentrated, and no counties were unconcentrated. Two percent of counties had low or no Medicare Advantage enrollment. 

Medicare Advantage markets were more concentrated in rural counties than in urban counties: 39% of the most rural counties were very highly concentrated in 2024, compared with 15% of rural counties that were near urban areas and 6% of urban counties.

Nine in 10 Medicare beneficiaries lived in a county where at least half of all Medicare Advantage enrollees were in plans sponsored by one or two insurers in 2024.

UnitedHealthcare (41%) or Humana (25%) had the highest enrollment in two-thirds of counties, which comprised 59% of all Medicare Advantage enrollment, in 2024. Among all Medicare Advantage insurers, UnitedHealthcare was the dominant insurer in the largest share of highly concentrated markets (41%) and very highly concentrated markets (50%).

In more than four in 10 counties, comprising 22% of all Medicare Advantage enrollment, a single Medicare Advantage insurer had at least 50% of enrollment in 2024, including 22% of counties where UnitedHealthcare had at least 50% of enrollment and 10% of counties where Humana had at least 50% of enrollment. Some large counties where one insurer had at least 50% of enrollment include Dallas County, Texas (55%), Salt Lake County, Utah (52%) and Milwaukee County, Wisconsin (64%).

WHAT’S THE IMPACT

According to the analysis, higher market concentration in Medicare Advantage insurance markets may lower the incentive for insurers to compete for potential enrollees by making plans more appealing through more comprehensive benefits or lower costs.

Yet the lack of competitiveness in MA markets hasn’t been addressed by lawmakers in recent years. The most recent activity at the federal level occurred in 2017 when the Department of Justice blocked a merger between insurers Aetna and Humana, arguing if it went through it would significantly raise market concentration in the Medicare Advantage market. 

More recently, the conversation regarding competition in healthcare has revolved around increased consolidation in provider markets, especially hospitals and health systems, said KFF.

THE LARGER TREND

The annual 2025 Medicare Advantage competitive enrollment report by healthcare advisory firm Chartis and consulting firm HealthScape Advisors said the Medicare Advantage market is undergoing a period of correction, with growth decelerating following rapid growth in the early 2020s.

Despite the numbers, the market remains strong, the report said. Health plan leaders are optimistic and generally more positive than when they were surveyed last year, and the MA market has continued growth and favorable economics compared to other market segments, it said. Also, the Trump administration has signaled support for the program, and less administrative burden is expected for plans.

Ninety-one percent expect the same or better performance in 2026, compared to 74% the year prior.