Three or fewer health insurers held at least 80 percent of enrollment on the ACA individual exchanges in 49 of 51 states in 2024, the Government Accountability Office reported October 16. Concentration was generally higher in 2024 than in 2011 in all three private insurance markets GAO studied.
What counts as "concentrated"
GAO's test, stated in the report: "We considered states' overall markets or exchanges to be concentrated if three or fewer issuers held at least 80 percent of the market share of enrollment." It applied that test to each state's individual, small-group and large-group market using 2011 through 2024 data, and to the individual exchanges — which sit inside the individual market — using 2015 through 2024 data. The measure is a share of enrollment, counted as covered life-years: the average number of lives insured, dependents included, across the year rather than a head count on one day. Issuers sharing a parent company were counted as one, and "state" includes the District of Columbia, so each count runs to 51. Where a market had fewer than three issuers, GAO says it still calls the measure the three largest issuers and counted the one or two that existed.
The three markets, and the exchanges
Counting states where three or fewer issuers held at least 80 percent of enrollment:
- Large-group (coverage offered by large employers, the biggest of the three markets, an average of about 39.3 million enrollees in 2024): 40 states in 2011 to 45 in 2024.
- Small-group (coverage offered by small employers, an average of about 10 million): 36 to 47.
- Individual market overall (an average of 23.4 million): 33 to 36, after rising to 47 states in 2019.
- Individual exchanges, the marketplaces the Affordable Care Act required in each state (an average of 21.9 million, counted inside the individual-market figure above): 47 states in 2015 to 49 in 2024, after reaching all 51 in 2020.
Single-issuer concentration — one issuer alone above 80 percent — moved the other way in two markets: by 2024 it was down to one state each in the individual market and the exchanges, but up to 16 states in small-group and 13 in large-group.
What can affect concentration
GAO lists factors that can affect concentration rather than explaining this period's change. Increased concentration, it says, has often been the result of consolidation — mergers and acquisitions among existing issuers — and can also increase when issuers leave a market or when larger issuers gain share from smaller ones. It says concentration can persist because it can be difficult for new issuers to enter, and can decrease when new issuers do enter. Issuer counts fell: the median number of individual-market issuers per state went from 30 in 2011 to nine in 2024, and small-group issuers from 13 to five.
What it does not say
The individual, small-group and large-group figures come from Medical Loss Ratio data issuers report annually to CMS for 2011 through 2024; the exchange figures come from a CMS data warehouse, CMS's risk-adjustment program and data collected from states, for 2015 through 2024. GAO says the Medical Loss Ratio data do not include self-funded health plans — almost two-thirds of workers with employer coverage were enrolled in such plans in 2024 — and that for the two group markets they cover fully insured plans only. GAO says it did not otherwise independently verify the accuracy or completeness of the information with the issuers. Its counts are statewide except on the exchanges, where it averages across a state's rating areas; it notes a state may have multiple local markets with differing concentrations. GAO says research studies have found strong evidence that concentration is associated with higher consumer premiums, but the report does not measure premiums and makes no recommendations. It responds to a provision of the Affordable Care Act for GAO to periodically study health insurance market concentration; HHS provided technical comments on a draft.