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How concentrated the auto insurance market is, nationally and by state
Four groups write about 59% of U.S. personal auto premiums, but state leaders differ. How the data is built, what the HHI means, and how to check your state.
The U.S. personal auto market is concentrated at the top and crowded underneath. NAIC data for 2025, reported in March 2026, puts the four largest groups at roughly 59% of premiums, and the seven largest at about 72%. But more than 250 insurers and groups sold private passenger auto coverage in 2023, and in any one state the leaders can be a different set of names entirely, including regional carriers that never appear in national rankings.
For a shopper, the useful questions are narrower than "is the market too concentrated." Who dominates in your state? Are there enough competitors that quotes will genuinely differ? And does a high concentration number tell you anything about price? This article explains how the numbers are built, how regulators read them, and how to look up your own state.
Where the national numbers come from
Market share in auto insurance is calculated from premiums that insurers report to regulators on their annual statutory statements. The NAIC compiles these filings into market share reports, and state insurance departments publish their own cuts of the same data. The basic unit is direct written premium: premium collected on policies the insurer itself wrote, before reinsurance. A separate article, NAIC market share reports: who writes auto insurance in your state, walks through the reports line by line.
The most recent national snapshot is for calendar 2025. Repairer Driven News reported in March 2026 that, in NAIC data, State Farm held 18.64% of the market and Progressive 18.60%, with GEICO at 11.56% and Allstate at 10.15%. Those four combine for 58.95%. USAA (6.19%), Farmers (3.57%) and Liberty Mutual (2.81%) bring the seven to 71.52%, and the article says every other insurer holds less than 2%. Our own insurer profiles use the NAIC 2025 ranking, which shows the same order.
Two details matter. First, these are not all brands. Several insurers you can name separately roll up into one NAIC group; GEICO sits inside the Berkshire Hathaway group, for example. Second, the figures describe premium, not customers. A group that sells expensive coverage in high-cost states will show a bigger share than one with the same number of policies in cheaper states.
Group share versus company share
A "company" is a single legal entity licensed to sell insurance. A "group" is a set of companies under common ownership. Large insurers often write auto through several companies in the same state, each with its own rates and underwriting rules, so a company-level table can make a leader look smaller than it is. That is why regulators usually rank groups. The Maryland Insurance Administration explains in its 2025 competitive rating report that it ranks insurer groups rather than individual companies because groups stay comparable from year to year even when companies merge or are acquired.
The NAIC's own Competition Database Report, 2023 edition (published February 2025), counts both groups with affiliated insurers and stand-alone insurers that belong to no group as sellers. Keeping stand-alone insurers in the count matters for mutuals and small regionals. For why one group can show up at several price points in the same ZIP code, see why big insurers run several brands under one parent company.
What the Herfindahl-Hirschman Index measures
Top-four share is easy to understand but throws away information. The Herfindahl-Hirschman Index (HHI) uses every seller. You square each seller's market share, expressed as a percentage, and add the results. A market with one seller scores 10,000. The NAIC's Competition Database Report gives the textbook example: ten sellers with 10% each score 1,000.
Squaring is what makes the index sensitive to size. A toy market makes the point:
| Market | Shares | HHI |
|---|---|---|
| Ten equal sellers | 10% each | 1,000 |
| Four sellers | 40%, 30%, 20%, 10% | 1,600 + 900 + 400 + 100 = 3,000 |
| One leader, many followers | 40% plus sixty sellers at 1% each | 1,600 + 60 = 1,660 |
Now apply it to the 2025 shares above. Squaring the seven named shares gives about 347 + 346 + 134 + 103 + 38 + 13 + 8, or roughly 989. The remaining 28.5% is split among insurers each below 2%, which can add at most about 57 more points. So the national HHI for 2025 is somewhere near 1,000 to 1,050 on a group basis. This is our arithmetic from the published shares, not an NAIC figure, and it assumes the share table is a fair stand-in for premium. For comparison, the NAIC report's countrywide figure for 2023 private passenger auto is an HHI of 916, with a top-four share of 55.92% and 256 sellers.
How regulators read the number
There is no single legal line. The NAIC report says there is no precise point at which an HHI shows a market is concentrated enough to restrict competition, and points to the federal antitrust agencies' merger guidelines. The 2023 Merger Guidelines treat markets above 1,800 as highly concentrated and a change of more than 100 points as a significant increase. The NAIC report describes the older convention of 1,000 to 1,800 as moderately concentrated, and Maryland's report uses the same bands.
Those thresholds were written to screen mergers, not to grade a state's insurance market. The NAIC adds that when the top four sellers exceed 50%, concentration deserves at least a closer look, while stressing that there is no formal way to determine competitiveness from that number alone.
The national picture versus the state picture
Insurance is regulated and sold state by state, so the state tables matter more than the national one. The Competition Database Report lists every state. Here is a sample of the private passenger auto totals for 2023, ordered from least to most concentrated by HHI:
| State | Top-four share | HHI | Sellers |
|---|---|---|---|
| California | 43.87% | 790 | 66 |
| Utah | 49.50% | 846 | 54 |
| Texas | 56.14% | 1,025 | 70 |
| Maryland | 65.15% | 1,322 | 48 |
| Florida | 70.76% | 1,425 | 53 |
| New York | 70.87% | 1,508 | 43 |
| Louisiana | 73.57% | 1,711 | 39 |
| Alaska | 77.89% | 1,868 | 22 |
The District of Columbia scores 1,898 (74.21%, 26 sellers), the highest in the table. Treat the exact digits as one edition's snapshot: Maryland's own report puts its 2024 HHI at 1,301, with 144 companies writing private passenger auto, 63 of them in a top-ten group. The pattern is stable, though. Large states with many writers sit near or below 1,000, and small or heavily regulated markets are more concentrated because fewer companies find them worth the cost of entering.
Why regional carriers lead in some states
National rankings hide a lot of local strength. The Ohio Department of Insurance publishes a top-70 table of private passenger auto groups for 2025, built from the NAIC database as of June 2026. State Farm and Progressive are essentially tied at the top in Ohio, at 21.8% and 21.5%. Behind Allstate (11.6%) and GEICO's group (6.5%), the next names are Erie Insurance Group (4.8%) and Grange Mutual Casualty Group (3.8%), with Auto-Owners, Westfield and others in the top dozen. Grange is rarely mentioned in national comparisons, yet it outranks USAA's group, Nationwide, Liberty Mutual and Auto-Owners in this table.
The reasons are structural. Many regional insurers are mutuals or reciprocal exchanges that grew from a home territory, sell through local agents, and know their loss patterns closely. Farm bureau insurers and state-focused carriers often hold their positions by pairing auto with home and farm coverage. A carrier that is 1% nationally can be a top-five choice in its home state. Our guide to regional car insurers: when smaller carriers can beat the giants profiles several of them, and Erie Insurance is a good example of a regional group with a multi-state reach.
Does concentration change prices or choices?
It can, but the data does not give a simple answer. In theory, fewer sellers means less pressure to cut rates, and more sellers means more quotes to compare. In practice, auto insurance prices are driven mostly by claim costs, which differ by state because of weather, litigation, medical costs, traffic and repair prices. The NAIC's 2022/2023 Auto Insurance Database Report lists those factors and cautions that direct comparisons between states should be treated with a high degree of caution.
A look at the two NAIC reports side by side shows why. Florida, Louisiana and New York were the three highest-cost states in the 2023 expenditure table, and all three score above 1,400 on the HHI. But North Dakota and Maine, at the other end of the price scale, scored about 1,060 and 960 on the HHI, and California, with the lowest HHI, is not among the cheapest states. High claim costs push prices up, and they can also push marginal insurers out, which raises concentration. The two measures move together without one proving the other.
What concentration does imply for shoppers is practical. In a market with 22 sellers, as in Alaska, fewer carriers will quote you at all. In a market with 70 or more, there is more room for quotes to scatter, so quoting widely is more valuable. Maryland's regulators use an additional signal: the share held by the residual insurer that takes drivers other companies reject. They note that the Maryland Auto Insurance Fund's share stayed at 1.6% in 2023 and 2024, and read a low and stable share as a sign that voluntary insurers are still competing for riskier drivers. The same logic is in why two insurers quote the same driver very different prices.
How to find your state's top writers
Follow this process; it takes about ten minutes:
- Search for your state insurance department's "market share report" or "market share for top insurance groups." Several states, including Ohio, publish a private passenger auto table that ranks groups by direct written premium.
- Check the year and the lines included. Make sure it says private passenger auto, not all auto, and that it lists groups rather than single companies. If not, the NAIC's market share reports let you filter by line.
- Add the top four shares yourself. If the total is above 50%, your state is the kind of market the NAIC says deserves a second look.
- Note which names you do not recognize in the top ten. Those are your regional options, and they are often worth a quote.
- Compare against the NAIC Competition Database Report for your state's HHI and seller count, and against the year-over-year trend if your state tracks it.
- Build your quote list from the top four and at least two regional names, then use compare auto insurers side by side to put the offers side by side. Rules differ by state, so use state car insurance requirements lookup to confirm minimum coverage first.
Mistakes people make with market-share data
- Reading share as quality. Market share measures premium volume. It says nothing about claims service, financial strength or price. Use ratings and complaint data for those, as described in What NAIC auto insurance data measures.
- Mixing years and bases. The 2023 Competition Database figures and the 2025 national share figures cover different years. Premium rises with rates, so shares can shift because of price changes as well as customer changes.
- Treating an HHI as a verdict. The index depends on how the market is defined. A statewide private passenger auto total lumps together urban and rural drivers, standard and nonstandard coverage, and sellers that only write renewals. The NAIC itself notes its data cannot separate sellers open to new business from sellers writing only renewals.
- Ignoring the pattern in a soft or hard cycle. Exits and entries change when profits change; see hard and soft markets: why car insurance prices move in cycles.
Common questions
Is it a problem that so few companies write so much of the market?
Not by itself. Regulators look at concentration alongside the number of sellers, entry and exit, profitability and price changes. A leader with a large share can still face active competition if many insurers sell in the state and drivers switch easily. Concentration is a reason to look closely, not a conclusion.
Why do State Farm and Progressive appear almost tied nationally but not in every state?
Because each state has its own history. State Farm built its agent force over decades in some places, and Progressive grew faster through direct sales and price comparison in others. In Ohio the two are within a point of each other, but in many smaller states one or the other leads clearly, and a regional carrier may rank third.
Does a regional insurer have to be small to be good?
No. Size shows up in the share table, but financial strength and service are separate checks. Look at the insurer's AM Best rating and the NAIC complaint index, and ask whether it sells in your ZIP code at all.
Can I find out how many insurers actually sell to new customers in my state?
Not from the share tables. The NAIC says its data does not distinguish between sellers open to new and renewal business. The best proxy is to run quotes; an insurer that declines to quote, or whose agent says it is not writing new policies, is effectively not in your market that month.
Key takeaways
- NAIC data for 2025 puts the top four groups at about 59% of U.S. personal auto premium and the top seven at about 72%, but hundreds of other insurers sell in individual states.
- Group share is the right unit: one group can include several brands and companies with different rates.
- The HHI squares each seller's share; the NAIC reported 916 countrywide for 2023, and its guidance is explicit that there is no formal cutoff for "too concentrated."
- State pictures vary widely: California scored 790 on the 2023 HHI, Alaska 1,868 and the District of Columbia 1,898. Regional carriers such as Erie and Grange place in Ohio's top ten.
- Use your state insurance department's market share table to build a quote list; concentration is a clue about choices, not a prediction of price.