Medicare Advantage markets remain highly concentrated across the U.S., according to the American Medical Association’s new report, “Competition in Health Insurance: A Comprehensive Study of U.S. Markets.”
AMA researchers analyzed data from 2024 across 384 metropolitan areas, all 50 states and the District of Columbia for the study, and found that the vast majority of health insurance markets are highly concentrated.
Here are five takeaways from the report:
- In 2025, 54% of eligible Medicare beneficiaries were enrolled in Medicare Advantage, up sharply from 19% in 2007, making MA an increasingly critical market to monitor.
- The average MA Herfindahl-Hirschman Index, a measurement of a firm’s market size, was 3,056 in 2024, down from 3,923 in 2017, but still well above federal thresholds for a highly concentrated market.
- While average HHI declined in 2023 and 2024, the year-to-year decreases were much smaller than those seen earlier in the seven-year study period.
- At the metropolitan level, MA markets saw more insurers and lower average market shares over time. Nationally, however, UnitedHealth Group’s MA share rose from 25% in 2017 to 30% in 2024.
- In 2024, 97% of Medicare Advantage markets met the definition of highly concentrated — only a marginal improvement from 99% in 2017.
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