Updated November 2026 with the latest American Medical Association data (enrollment as of 2024). In most states, one health insurer controls a large share of the market. A Blue Cross Blue Shield company is the largest commercial health insurer in 43 of 50 states and the District of Columbia, and in 15 states a single insurer holds at least half of the commercial market, according to the American Medical Association’s (AMA) Competition in Health Insurance report.
This page shows, for every state, the two largest insurers and their market shares in three markets: commercial coverage (employer plans and individual coverage combined), the ACA Marketplace exchanges and Medicare Advantage. It also shows each market’s Herfindahl-Hirschman Index (HHI), the standard measure of market concentration used by antitrust regulators.
Key Findings
- The most concentrated states: Alabama (84%), Kentucky (76%), Hawaii (66%), Michigan (65%), Illinois (62%), measured by the largest insurer’s share of the commercial market.
- Highly concentrated almost everywhere: 47 of 51 statewide commercial markets have an HHI above 1,800, the level federal merger guidelines call highly concentrated. The AMA found 97% of metropolitan-area markets were highly concentrated.
- The most competitive states: Oregon (HHI 1,452), New York (HHI 1,536), Washington (HHI 1,609), Wisconsin (HHI 1,616).
- Medicare Advantage: UnitedHealth Group is the largest Medicare Advantage insurer in 30 states and Humana in 9.
- ACA exchanges: Centene (Ambetter) leads the Marketplace in 12 states, and one insurer has at least half of exchange enrollment in 21 states.
What the HHI Measures
The Herfindahl-Hirschman Index adds up the squares of every insurer’s market share. A market with one insurer scores 10,000; a market split evenly among ten insurers scores 1,000. The U.S. Department of Justice and Federal Trade Commission’s 2023 Merger Guidelines treat a market with an HHI above 1,800 as highly concentrated. In concentrated markets, insurers have more leverage over premiums and over the rates they pay doctors and hospitals.
Commercial Health Insurance Market Share by State
Combined PPO, HMO, POS and ACA exchange enrollment, as of January 1, 2024. States with a Health Plan News state guide are linked.
| State | Largest Insurer | Share | Second-Largest Insurer | Share | HHI |
|---|---|---|---|---|---|
| Alabama | Blue Cross and Blue Shield of Alabama | 84% | UnitedHealth Group | 6% | 7,193 |
| Alaska | Premera | 47% | CVS Health (Aetna) | 42% | 4,058 |
| Arizona | UnitedHealth Group | 30% | Blue Cross and Blue Shield of Arizona | 26% | 2,370 |
| Arkansas | Blue Cross and Blue Shield of Arkansas | 41% | Centene (Ambetter) | 22% | 2,711 |
| California | Kaiser Permanente | 36% | Elevance Health (Anthem) | 24% | 2,194 |
| Colorado | UnitedHealth Group | 27% | Elevance Health (Anthem) | 25% | 2,152 |
| Connecticut | Elevance Health (Anthem) | 38% | UnitedHealth Group | 21% | 2,492 |
| Delaware | Highmark (Blue Cross Blue Shield) | 58% | CVS Health (Aetna) | 23% | 4,021 |
| District of Columbia | CareFirst BlueCross BlueShield | 30% | CVS Health (Aetna) | 22% | 1,960 |
| Florida | Blue Cross and Blue Shield of Florida | 34% | UnitedHealth Group | 18% | 2,073 |
| Georgia | Elevance Health (Anthem) | 35% | CVS Health (Aetna) | 15% | 1,920 |
| Hawaii | HMSA (Blue Cross Blue Shield of Hawaii) | 66% | Kaiser Permanente | 21% | 4,890 |
| Idaho | Blue Cross of Idaho | 40% | Cambia (Regence) | 17% | 2,210 |
| Illinois | Health Care Service Corp. (Blue Cross and Blue Shield of Illinois) | 62% | UnitedHealth Group | 15% | 4,284 |
| Indiana | Elevance Health (Anthem) | 57% | UnitedHealth Group | 16% | 3,642 |
| Iowa | Wellmark Blue Cross Blue Shield | 46% | UnitedHealth Group | 28% | 3,061 |
| Kansas | Blue Cross and Blue Shield of Kansas | 42% | UnitedHealth Group | 17% | 2,520 |
| Kentucky | Elevance Health (Anthem) | 76% | UnitedHealth Group | 12% | 5,960 |
| Louisiana | Blue Cross and Blue Shield of Louisiana | 62% | UnitedHealth Group | 20% | 4,332 |
| Maine | Elevance Health (Anthem) | 44% | CVS Health (Aetna) | 15% | 2,642 |
| Maryland | CareFirst BlueCross BlueShield | 44% | UnitedHealth Group | 17% | 2,698 |
| Massachusetts | Blue Cross and Blue Shield of Massachusetts | 36% | Point32Health | 32% | 2,496 |
| Michigan | Blue Cross and Blue Shield of Michigan | 65% | Corewell Health (Priority Health) | 13% | 4,484 |
| Minnesota | Blue Cross and Blue Shield of Minnesota | 37% | HealthPartners | 21% | 2,346 |
| Mississippi | Blue Cross and Blue Shield of Mississippi | 45% | Centene (Ambetter) | 19% | 2,816 |
| Missouri | Elevance Health (Anthem) | 30% | UnitedHealth Group | 27% | 2,017 |
| Montana | Health Care Service Corp. (Blue Cross and Blue Shield of Montana) | 52% | Cigna | 16% | 3,260 |
| Nebraska | Blue Cross and Blue Shield of Nebraska | 44% | UnitedHealth Group | 27% | 2,872 |
| Nevada | UnitedHealth Group | 37% | Elevance Health (Anthem) | 26% | 2,427 |
| New Hampshire | Elevance Health (Anthem) | 51% | Cigna | 16% | 3,164 |
| New Jersey | Horizon Blue Cross Blue Shield of New Jersey | 38% | CVS Health (Aetna) | 28% | 2,634 |
| New Mexico | Health Care Service Corp. (Blue Cross and Blue Shield of New Mexico) | 43% | Presbyterian Health Plan | 21% | 2,669 |
| New York | UnitedHealth Group | 28% | Elevance Health (Anthem) | 17% | 1,536 |
| North Carolina | Blue Cross and Blue Shield of North Carolina | 47% | CVS Health (Aetna) | 19% | 2,982 |
| North Dakota | Blue Cross and Blue Shield of North Dakota | 50% | Sanford | 32% | 3,569 |
| Ohio | Elevance Health (Anthem) | 36% | Medical Mutual of Ohio | 19% | 2,157 |
| Oklahoma | Health Care Service Corp. (Blue Cross and Blue Shield of Oklahoma) | 57% | UnitedHealth Group | 15% | 3,663 |
| Oregon | Cambia (Regence) | 22% | Kaiser Permanente | 18% | 1,452 |
| Pennsylvania | Highmark (Blue Cross Blue Shield) | 32% | Independence Health Group | 18% | 1,842 |
| Rhode Island | Blue Cross and Blue Shield of Rhode Island | 39% | UnitedHealth Group | 29% | 2,623 |
| South Carolina | Blue Cross and Blue Shield of South Carolina | 56% | UnitedHealth Group | 13% | 3,615 |
| South Dakota | Wellmark Blue Cross Blue Shield | 40% | Sanford | 26% | 2,730 |
| Tennessee | Blue Cross and Blue Shield of Tennessee | 41% | Cigna | 22% | 2,615 |
| Texas | Health Care Service Corp. (Blue Cross and Blue Shield of Texas) | 45% | UnitedHealth Group | 21% | 2,762 |
| Utah | Intermountain Health (SelectHealth) | 44% | CVS Health (Aetna) | 16% | 2,617 |
| Vermont | Blue Cross Blue Shield of Michigan (affiliate Blue Cross and Blue Shield of Vermont) | 59% | Cigna | 22% | 4,054 |
| Virginia | Elevance Health (Anthem) | 43% | CVS Health (Aetna) | 14% | 2,411 |
| Washington | Cambia (Regence) | 22% | Premera | 21% | 1,609 |
| West Virginia | Highmark (Blue Cross Blue Shield) | 59% | UnitedHealth Group | 11% | 3,822 |
| Wisconsin | UnitedHealth Group | 29% | Elevance Health (Anthem) | 22% | 1,616 |
| Wyoming | Cigna | 36% | Blue Cross and Blue Shield of Wyoming | 24% | 2,394 |
Medicare Advantage Market Share by State
Medicare Advantage enrollment as of January 1, 2024. Alaska has too few Medicare Advantage enrollees to report.
| State | Largest Insurer | Share | Second-Largest Insurer | Share | HHI |
|---|---|---|---|---|---|
| Alabama | UnitedHealth Group | 43% | Humana | 18% | 2,619 |
| Arizona | UnitedHealth Group | 48% | Humana | 18% | 2,789 |
| Arkansas | UnitedHealth Group | 45% | Humana | 25% | 2,959 |
| California | Kaiser Permanente | 42% | UnitedHealth Group | 17% | 2,256 |
| Colorado | UnitedHealth Group | 49% | Kaiser Permanente | 21% | 3,252 |
| Connecticut | UnitedHealth Group | 43% | CVS Health (Aetna) | 31% | 3,016 |
| Delaware | UnitedHealth Group | 37% | CVS Health (Aetna) | 29% | 2,644 |
| District of Columbia | UnitedHealth Group | 64% | Kaiser Permanente | 22% | 4,680 |
| Florida | Humana | 32% | UnitedHealth Group | 30% | 2,170 |
| Georgia | UnitedHealth Group | 34% | Humana | 32% | 2,547 |
| Hawaii | UnitedHealth Group | 30% | Kaiser Permanente | 22% | 2,177 |
| Idaho | UnitedHealth Group | 36% | Blue Cross of Idaho | 35% | 2,686 |
| Illinois | CVS Health (Aetna) | 31% | Humana | 25% | 2,124 |
| Indiana | UnitedHealth Group | 36% | Humana | 28% | 2,695 |
| Iowa | UnitedHealth Group | 40% | CVS Health (Aetna) | 28% | 2,746 |
| Kansas | UnitedHealth Group | 36% | CVS Health (Aetna) | 29% | 2,735 |
| Kentucky | Humana | 41% | Elevance Health (Anthem) | 27% | 2,851 |
| Louisiana | Humana | 45% | UnitedHealth Group | 33% | 3,317 |
| Maine | Martin’s Point Health Care | 30% | UnitedHealth Group | 20% | 1,936 |
| Maryland | UnitedHealth Group | 31% | Kaiser Permanente | 28% | 2,126 |
| Massachusetts | UnitedHealth Group | 26% | Point32Health | 25% | 1,777 |
| Michigan | Blue Cross and Blue Shield of Michigan | 42% | Corewell Health (Priority Health) | 18% | 2,416 |
| Minnesota | Blue Cross and Blue Shield of Minnesota | 34% | UCare | 22% | 2,063 |
| Mississippi | Humana | 52% | UnitedHealth Group | 21% | 3,389 |
| Missouri | UnitedHealth Group | 48% | CVS Health (Aetna) | 17% | 2,947 |
| Montana | Humana | 60% | Health Care Service Corp. (Blue Cross and Blue Shield of Montana) | 23% | 4,303 |
| Nebraska | UnitedHealth Group | 54% | CVS Health (Aetna) | 16% | 3,459 |
| Nevada | UnitedHealth Group | 36% | Humana | 30% | 2,492 |
| New Hampshire | UnitedHealth Group | 34% | Elevance Health (Anthem) | 16% | 1,954 |
| New Jersey | CVS Health (Aetna) | 34% | UnitedHealth Group | 34% | 2,551 |
| New Mexico | Presbyterian Health Plan | 27% | UnitedHealth Group | 26% | 2,199 |
| New York | UnitedHealth Group | 23% | Healthfirst | 14% | 1,250 |
| North Carolina | Humana | 37% | UnitedHealth Group | 33% | 2,799 |
| North Dakota | Medica | 39% | Blue Cross and Blue Shield of North Dakota | 28% | 2,684 |
| Ohio | UnitedHealth Group | 23% | Elevance Health (Anthem) | 23% | 1,777 |
| Oklahoma | UnitedHealth Group | 51% | Humana | 25% | 3,361 |
| Oregon | UnitedHealth Group | 26% | Kaiser Permanente | 15% | 1,405 |
| Pennsylvania | CVS Health (Aetna) | 28% | Highmark (Blue Cross Blue Shield) | 18% | 1,610 |
| Rhode Island | Blue Cross and Blue Shield of Rhode Island | 57% | UnitedHealth Group | 36% | 4,624 |
| South Carolina | Humana | 40% | UnitedHealth Group | 31% | 2,850 |
| South Dakota | Medica | 46% | Humana | 18% | 2,864 |
| Tennessee | UnitedHealth Group | 27% | Humana | 27% | 2,190 |
| Texas | UnitedHealth Group | 50% | Humana | 18% | 3,008 |
| Utah | UnitedHealth Group | 54% | Intermountain Health (SelectHealth) | 18% | 3,425 |
| Vermont | UnitedHealth Group | 44% | Blue Cross Blue Shield of Michigan (affiliate Blue Cross and Blue Shield of Vermont) | 25% | 2,851 |
| Virginia | Humana | 32% | UnitedHealth Group | 28% | 2,293 |
| Washington | UnitedHealth Group | 37% | Kaiser Permanente | 18% | 2,070 |
| West Virginia | Humana | 51% | CVS Health (Aetna) | 22% | 3,401 |
| Wisconsin | UnitedHealth Group | 45% | Humana | 12% | 2,477 |
| Wyoming | UnitedHealth Group | 86% | CVS Health (Aetna) | 7% | 7,416 |
For 2027 plan counts and premiums in each state, see our Medicare Advantage plans by state page.
ACA Marketplace (Exchange) Market Share by State
Exchange enrollment as of July 1, 2024. Several insurers have since left or entered state Marketplaces; our state guides list 2026 and 2027 insurers.
| State | Largest Insurer | Share | Second-Largest Insurer | Share | HHI |
|---|---|---|---|---|---|
| Alabama | Blue Cross and Blue Shield of Alabama | 70% | Centene (Ambetter) | 24% | 5,589 |
| Alaska | Premera | 71% | Moda Health | 29% | 5,895 |
| Arizona | CVS Health (Aetna) | 37% | UnitedHealth Group | 20% | 2,480 |
| Arkansas | Centene (Ambetter) | 67% | Blue Cross and Blue Shield of Arkansas | 33% | 5,550 |
| California | Kaiser Permanente | 34% | Blue Shield of California | 26% | 2,199 |
| Colorado | Elevance Health (Anthem) | 29% | Kaiser Permanente | 23% | 2,269 |
| Connecticut | EmblemHealth | 61% | Elevance Health (Anthem) | 39% | 5,225 |
| Delaware | Highmark (Blue Cross Blue Shield) | 70% | CVS Health (Aetna) | 11% | 5,179 |
| District of Columbia | CareFirst BlueCross BlueShield | 81% | Kaiser Permanente | 19% | 6,895 |
| Florida | Blue Cross and Blue Shield of Florida | 37% | Centene (Ambetter) | 19% | 2,360 |
| Georgia | Centene (Ambetter) | 41% | Oscar | 24% | 2,518 |
| Hawaii | HMSA (Blue Cross Blue Shield of Hawaii) | 61% | Kaiser Permanente | 39% | 5,251 |
| Idaho | Intermountain Health (SelectHealth) | 34% | Cambia (Regence) | 26% | 2,319 |
| Illinois | Health Care Service Corp. (Blue Cross and Blue Shield of Illinois) | 52% | Centene (Ambetter) | 15% | 3,290 |
| Indiana | Centene (Ambetter) | 36% | CareSource | 29% | 2,963 |
| Iowa | Wellmark Blue Cross Blue Shield | 74% | Oscar | 16% | 5,800 |
| Kansas | Centene (Ambetter) | 47% | Blue Cross and Blue Shield of Kansas | 17% | 2,970 |
| Kentucky | Elevance Health (Anthem) | 42% | Centene (Ambetter) | 29% | 3,360 |
| Louisiana | Centene (Ambetter) | 33% | Blue Cross and Blue Shield of Louisiana | 29% | 2,888 |
| Maine | Elevance Health (Anthem) | 41% | Community Health Options | 31% | 3,362 |
| Maryland | CareFirst BlueCross BlueShield | 48% | UnitedHealth Group | 28% | 3,612 |
| Massachusetts | Point32Health | 56% | Boston Medical Center (WellSense Health Plan) | 30% | 4,045 |
| Michigan | Blue Cross and Blue Shield of Michigan | 32% | Centene (Ambetter) | 29% | 2,335 |
| Minnesota | UCare | 38% | Blue Cross and Blue Shield of Minnesota | 27% | 2,769 |
| Mississippi | Centene (Ambetter) | 67% | Cigna | 19% | 4,912 |
| Missouri | Centene (Ambetter) | 42% | Elevance Health (Anthem) | 25% | 2,681 |
| Montana | Health Care Service Corp. (Blue Cross and Blue Shield of Montana) | 54% | Mountain Health CO-OP | 31% | 4,067 |
| Nebraska | Centene (Ambetter) | 56% | Medica | 34% | 4,395 |
| Nevada | UnitedHealth Group | 38% | Elevance Health (Anthem) | 21% | 2,336 |
| New Hampshire | Elevance Health (Anthem) | 70% | Centene (Ambetter) | 26% | 5,641 |
| New Jersey | Horizon Blue Cross Blue Shield of New Jersey | 35% | Independence Health Group | 35% | 2,989 |
| New Mexico | Health Care Service Corp. (Blue Cross and Blue Shield of New Mexico) | 47% | Presbyterian Health Plan | 23% | 3,073 |
| New York | Centene (Ambetter) | 39% | Healthfirst | 22% | 2,243 |
| North Carolina | Blue Cross and Blue Shield of North Carolina | 39% | CVS Health (Aetna) | 37% | 3,119 |
| North Dakota | Blue Cross and Blue Shield of North Dakota | 68% | Sanford | 26% | 5,399 |
| Ohio | Centene (Ambetter) | 18% | Elevance Health (Anthem) | 17% | 1,388 |
| Oklahoma | Health Care Service Corp. (Blue Cross and Blue Shield of Oklahoma) | 59% | Centene (Ambetter) | 16% | 3,916 |
| Oregon | Providence Health Plan | 25% | Cambia (Regence) | 23% | 2,081 |
| Pennsylvania | Independence Health Group | 29% | Highmark (Blue Cross Blue Shield) | 27% | 2,131 |
| Rhode Island | Neighborhood Health Plan of Rhode Island | 80% | Blue Cross and Blue Shield of Rhode Island | 20% | 6,855 |
| South Carolina | Blue Cross and Blue Shield of South Carolina | 45% | Centene (Ambetter) | 44% | 4,087 |
| South Dakota | Sanford | 45% | Wellmark Blue Cross Blue Shield | 28% | 3,555 |
| Tennessee | Centene (Ambetter) | 44% | Blue Cross and Blue Shield of Tennessee | 22% | 2,921 |
| Texas | Health Care Service Corp. (Blue Cross and Blue Shield of Texas) | 32% | Centene (Ambetter) | 21% | 1,972 |
| Utah | Intermountain Health (SelectHealth) | 66% | CVS Health (Aetna) | 23% | 4,880 |
| Vermont | Blue Cross Blue Shield of Michigan (affiliate Blue Cross and Blue Shield of Vermont) | 66% | MVP Health Care | 34% | 5,515 |
| Virginia | Elevance Health (Anthem) | 33% | Sentara Health Plans | 21% | 2,114 |
| Washington | Centene (Ambetter) | 32% | Molina Healthcare | 17% | 1,904 |
| West Virginia | Highmark (Blue Cross Blue Shield) | 56% | CareSource | 44% | 5,067 |
| Wisconsin | Elevance Health (Anthem) | 24% | Common Ground Healthcare Cooperative | 21% | 1,528 |
| Wyoming | Blue Cross and Blue Shield of Wyoming | 55% | Mountain Health CO-OP | 45% | 5,054 |
Why Market Concentration Matters
A dominant insurer can set the terms for employers shopping for group coverage, for hospitals and doctors negotiating payment rates, and for consumers who have few alternatives. Research cited by the AMA links insurer concentration to higher premiums and lower physician payments. Concentration also shapes what happens when a large insurer leaves a market, as Cigna, UnitedHealthcare and Molina are doing in several state Marketplaces for 2027; see our report on ACA Marketplace insurer exits.
Blue Cross Blue Shield plans dominate because each is licensed for a defined territory, and many have been the largest local insurer for decades. National carriers compete with them mostly in large employer accounts and in Medicare Advantage.
How To Use This Data
- When choosing a Marketplace plan, compare insurers beyond the largest one; smaller carriers often have lower premiums in exchange for narrower networks.
- Employers in concentrated markets can ask brokers about self-funded or level-funded options; see our guide to self-funded plans.
- Check each insurer’s claim denial record in our claim denial rankings.
- For company profiles, see our List of Health Insurance Companies.
Source
American Medical Association, Competition in Health Insurance: A Comprehensive Study of U.S. Markets, 2025 Update, Tables A-1, A-3 and A-4 (state-level rows). Shares are rounded to whole percentages by the AMA. Insurer names are shown with their local brand where helpful. Key findings are Health Plan News calculations from the AMA tables.