Claim frequency vs severity: which one actually moves premiums?

Both matter, but they matter as a pair. Frequency is how often claims happen per insured vehicle; severity is the average cost of each claim; multiply them and you get the loss cost that rates are built to cover. Since 2020 the pair has pulled apart: frequency fell and stayed below its pre-pandemic level, while severity, driven by repair and replacement costs, rose faster, so the product went up and so did prices.

That is why "fewer crashes" and "higher premiums" can both be true in the same year. This article defines the two measures with a numeric example, goes coverage by coverage, walks through the post-2020 period with dated sources, and shows where each number is published so you can check the claim yourself.

Two measures, one product

The Casualty Actuarial Society's textbook Basic Ratemaking (fifth edition, 2016) defines the pieces:

• Frequency is the rate at which claims occur: the number of claims divided by the number of exposures. An exposure is a unit of risk, usually one insured vehicle for one year.
• Severity is the average cost of a claim: total losses divided by the number of claims.
• Pure premium, also called loss cost, is losses divided by exposures. It equals frequency times severity.

The National Association of Insurance Commissioners (NAIC) uses the same formulas in its 2022/2023 Auto Insurance Database Report, expressing frequency as incurred claims per 100 earned exposures and severity as incurred losses divided by incurred claims.

The pure premium is not the price. It is the part of the price meant for claims. Expenses, commissions, taxes and a profit provision come on top, which is why a premium is larger than the loss cost. Our guide on loss ratios and rate filings shows how the two fit together.

A numeric example: why a drop in frequency can vanish

All numbers in this section are invented. Imagine an insurer with 100,000 insured vehicles and a collision book.

Frequency fell by a seventh and still the loss cost rose 6.25%, because severity grew more than enough to offset it. The break-even point is simple: if frequency falls 15%, severity has to rise 17.6% (1 divided by 0.85, minus one) for the loss cost to stay flat. Anything above that raises the cost of covering each vehicle.

Run it the other way. If severity rises 25% and frequency falls 20%, the loss cost is unchanged. The two factors compound just as the factors in a rating plan do (see our article on base rates and relativities). Reporters who cite only a frequency decline, or only a severity increase, are describing half the equation.

Turning loss cost into a premium

Say the insurer needs 70 cents of every premium dollar for claims and claim-handling, with the rest covering expenses and profit. The Year 2 loss cost of $510 implies a premium of about $729 ($510 divided by 0.70), and Year 1's $480 implies about $686. That difference of roughly 6.3% is the indicated increase before any other changes. Real indications also adjust for trend, development of open claims and the other items described in our worked indication.

Coverage by coverage: what drives each

The mix of frequency and severity differs by coverage, and so do the drivers of each.

The Highway Loss Data Institute (HLDI), a research arm of the Insurance Institute for Highway Safety, publishes loss fact sheets that split each coverage into frequency and severity. Its December 2025 sheets, based on 2022-24 model-year cars, pickups and SUVs insured under private passenger policies, give these all-vehicle averages:

Collision's 5.9 claims per 100 vehicles times $10,267 is the $604 HLDI reports, which shows the arithmetic in the real data. Property damage liability is rarer and cheaper per claim. Bodily injury is the reverse: the fewest claims, the highest severity. For comprehensive, the sheet breaks the loss into theft, glass and everything else, and the large "other" share reflects weather, fire, animal strikes and vandalism. HLDI notes that its overall losses exclude administrative costs, so the dollar amounts are loss cost, not the price on your bill.

What this means for each coverage

• Collision and property damage respond fastest to repair-cost inflation because severity is mostly parts and labor. The U.S. Bureau of Labor Statistics' consumer price index for motor vehicle maintenance and repair (not seasonally adjusted, U.S. city average) rose from 309.9 in December 2020 to 468.5 in September 2026, an increase of about 51%, according to figures retrieved through the BLS public data API for series CUUR0000SETD.
• Bodily injury changes slowly and then suddenly, because injury claims stay open for years and the cost depends on medical prices and on legal involvement. See our articles on medical costs and injury claims and attorney involvement.
• Comprehensive is the lumpiest. A hail season or a theft wave changes frequency and severity in the same year, and the effect is concentrated in particular regions.

Why frequency fell and severity rose after 2020

The post-2020 period is the clearest recent example, and three independent sources describe it.

The Insurance Research Council (IRC). In a July 2023 release on its Trends in Personal Auto Insurance Claims 2002-2022 report, the IRC said claim frequency plummeted during the 2020-2022 pandemic years while severity skyrocketed, especially for vehicle damage claims, partly because of inflationary pressure on replacement parts and body-repair labor. Over the full 2002-2022 span, frequency for physical damage liability and bodily injury claims declined more than 2% annualized while severity grew more than 4.5% annualized, so average loss costs rose. By 2022, the IRC said, loss costs for nearly every coverage had surpassed their 2019 level.

Milliman. In an October 2022 article, Milliman reported that the average change from year-end 2020 to year-end 2021 was a 0.6% increase in frequency and an 11.3% increase in severity, and that since 2021 collision severity had risen faster than property damage or comprehensive severity. It cited an average rate change of about +7.0% across more than 2,000 approved personal auto filings effective in 2022.

The CAS and Triple-I. An October 2024 summary of a joint study by the Casualty Actuarial Society and the Insurance Information Institute said claim frequency remained below pre-pandemic levels while severity continued to rise, with its compound growth rate nearly tripling from 3.6% a year in 2014-2019 to 9.8% a year in 2020-2023. The summary discusses both economic inflation and social inflation, meaning litigation trends that raise claim costs; our article on social inflation covers that part.

Put together: driving fell sharply in 2020, which reduced the number of claims, but each claim that did occur cost more because the price of repairing or replacing a vehicle was rising and injury claims were costing more to resolve. Frequency drifted back toward normal while severity stayed high. The product is the loss cost, and it climbed.

Changes that are not about how people drive

Frequency and severity can move for reasons that have little to do with crash behavior, and actuaries study them separately for that reason. Basic Ratemaking gives a clean illustration: if a company heavily markets a higher deductible, the shift lowers claim frequencies, because small losses never become claims, but is likely to raise severities, because the claims that remain are larger on average. Looking only at pure premium can hide that shift.

Several other things behave the same way:

• Policyholder behavior. When drivers skip small claims to protect their record, claim counts fall and the average paid claim rises, even if the underlying damage has not changed.
• A shift in the mix of vehicles. Heavier, more sensor-laden vehicles raise collision severity for the whole pool. HLDI's fact sheets show how much severity differs by vehicle class and size, with luxury cars, luxury SUVs, vans and some sports cars above the collision average.
• How claims are counted. The NAIC's report cautions that some insurers count claims per accident and others per claimant, and that it has not determined the share filed each way, so frequency and severity can differ between companies partly because of counting.
• Legal and medical practices. In bodily injury, a change in settlement practices or in the share of claimants who hire lawyers moves severity without any change in crash rates. Our article on attorney involvement looks at that effect.

A second example: injury claims

Suppose a liability book has 100,000 vehicles and 800 bodily injury claims a year (0.8 per 100) at an average of $24,000. That is $19.2 million, or $192 per vehicle. If crashes with injuries fall 10% to 720 claims but the average rises 15% to $27,600, the total is $19.87 million, or about $199 per vehicle. The loss cost went up 3.5% even though injury claims fell by a tenth. Because injury claims can stay open for years, the insurer may not know the true average of the newest year for some time, so the estimate itself can be revised, which is why liability pricing is more cautious and slower to respond than collision pricing.

Why the premium lags the cost

Loss cost and price do not move together month to month. Basic Ratemaking's worked example trends losses from calendar year 2011 forward to policies written during 2013, a trend period of two and a half years for annual policies. In plain terms, the claims data behind a filing can be about two years old by the time the new rate is in use, and the new rate then applies to policies that run for six or 12 months. A severity jump in one year therefore reaches premiums over the next one to three years. Our timeline article on filing to your bill shows the last leg of that delay.

It also explains why a drop in frequency alone does not produce quick relief. If severity is still climbing, the indication can still point upward.

Where to find the numbers yourself

1. HLDI loss facts on the IIHS site publish frequency, severity and overall losses by coverage and vehicle class. Our guide to IIHS and HLDI loss data explains how to read them.
2. NAIC Auto Insurance Database Report gives pure premium, loss ratio, frequency and severity by state and coverage, and defines each term.
3. Insurance Research Council trend reports track claim frequency and severity over decades; summaries are free, full reports are for sale. See the IRC studies guide.
4. Triple-I and CAS studies analyze inflation in liability claims.
5. BLS consumer price indexes for motor vehicle repair, parts and used vehicles show the price movements that drive property-damage severity.
6. Your state's filings show the frequency and severity trends an insurer assumed when it asked for a change.

When you read a headline, check three things: which coverage it covers, which years, and whether the number is a frequency, a severity or the combined loss cost.

Common questions

If crashes are down, why is my premium up?

Because the premium follows loss cost, not crash counts. If each claim costs more, the total can rise even with fewer claims. In the example above, a 15% frequency drop was more than offset by a 25% severity rise.

Does a claim-free year lower my own rate?

Your own record is one factor in your rating, covered in our article on rating relativities. The base rate that your relativities multiply moves with the whole pool's frequency and severity, so a better record helps you relative to others but does not stop the base from rising.

Which coverage rose most?

It depends on the state and year. Milliman's 2022 analysis found collision severity rising faster than property damage or comprehensive severity since 2021, and the CAS-Triple-I study focused on liability. Check your own policy's coverage lines.

Can severity fall?

Yes. If vehicle values or repair prices drop, severity can fall, but insurers' filings use multi-year data and trend, so rates tend to fall more slowly than they rose. Our article on used-car prices and parts costs explains the lag.

Key takeaways

• Loss cost equals frequency times severity; a premium is built to cover that loss cost plus expenses and profit.
• A fall in frequency can be erased by a rise in severity: a 15% drop needs only a 17.6% severity rise to break even.
• Since 2020, IRC, Milliman and CAS/Triple-I sources describe lower frequency alongside sharply higher severity, especially for vehicle damage.
• Coverages differ: collision and property damage follow repair costs, bodily injury follows medical and legal costs, and comprehensive swings with weather and theft.
• Prices lag costs by roughly one to three years, so check which years a headline number covers.