Do interest rates and investment income change your premium?

Interest rates and investment income do affect car insurance prices, but in a small and delayed way, and they rarely show up as a visible discount. An insurer collects your premium before it pays claims and invests the money in the meantime, so the return on that money is a real source of income that can, in principle, allow a lower price. In practice, the sums are modest for a short-tail line like auto, and they are swamped by changes in claim costs, which have been moving much faster than yields.

This article explains the mechanism (called float), how some states count investment income in the rate calculation, what the very low-rate years did to insurers' margins, why higher yields do not automatically bring prices down, and how to find the investment line in an insurer's annual statement.

Float: the money held between premium and claim

Float is the pool of money an insurer holds between collecting premiums and paying claims. You pay your premium at the start of a policy term, six months or a year. The insurer does not owe most of it out immediately. It holds an unearned portion for the part of the term that has not yet passed, and it holds a claim reserve for claims that have happened but are not yet paid. The investment portfolio is the place those dollars sit.

Float is a feature of every insurance line. What differs by line is how long the money is held. Property damage and collision claims are typically settled in a matter of weeks or months. Injury claims take longer: the Insurance Research Council (IRC) found in its July 2026 study of claims closed from mid-2017 to mid-2022 that represented bodily injury claimants waited a median of nearly 440 days for closure (see the IRC's announcement). Compare that with liability lines such as medical malpractice or workers' compensation, where payments can run for many years. Auto is a short-tail line, which means its float is small relative to premium.

Where the money goes

The NAIC's Capital Markets Bureau tracks how insurers invest. Its year-end 2025 asset mix report put cash and invested assets of all U.S. property and casualty insurers at about $3.1 trillion. Of that, bonds were about $1.52 trillion, roughly 49 percent; common stocks about $1.0 trillion, roughly 32 percent, of which the NAIC said about half were affiliated holdings; and cash and short-term investments about $300 billion, roughly 10 percent. The NAIC said property and casualty insurers hold about half of the industry's cash and short-term investments because of their need for liquidity to meet shorter-duration liabilities and potential claims.

Those figures cover the entire property and casualty industry, not only auto insurers, and they include the capital the insurer holds, not just policyholder money. The point for this article is that the return depends on interest rates (for bonds and cash) and on markets (for stocks).

A worked example of float income

Here is a hypothetical, not an insurer's actual figures. Say an insurer collects $100 of premium and, on average, holds each dollar for nine months before the corresponding claim dollars go out.

• At a 4 percent yield, the income on that float is about $100 times 4 percent times 0.75, or $3.00.
• At a 1 percent yield, it is about $0.75.

If the insurer's combined ratio, claims and expenses as a share of premium, is 103, it loses $3.00 on underwriting for each $100 of premium. At a 4 percent yield, the float income roughly offsets that loss before taxes. At 1 percent, the same insurer ends up about $2.25 short. So a lower-yield environment pushes insurers to price for a lower combined ratio, and a higher-yield environment lets them tolerate a higher one.

Real calculations are more detailed. They use the actual timing of claim payments, taxes, the cost of holding capital, and a return on the insurer's own surplus, not just on policyholder money. But the direction is the point: investment income is a cushion that lets an insurer accept a combined ratio above 100, not a surplus that has to be handed to you.

How investment income enters a rate filing

A rate filing is the insurer's request to a state to use a set of rates. Investment income enters in one of two ways.

Explicitly. Some states require or invite the filer to show an investment income credit, often as part of a profit provision. Florida is a clear example. Under section 627.0651 of the Florida Statutes, insurers are to establish motor vehicle rates that allow a reasonable rate of return. When the Office of Insurance Regulation reviews whether a rate is excessive, inadequate or unfairly discriminatory, one of the factors it must consider is the investment income reasonably expected from investable premiums anticipated in the filing, plus income from currently invested assets representing unearned premium and loss reserves. The statute adds that this income does not include income from invested surplus. It also says rates are inadequate if they are clearly insufficient, together with the investment income attributable to them, to sustain projected losses and expenses. Read it in the Florida Statutes.

The statute also contemplates a positive underwriting profit allowance that is compatible with a reasonable rate of return plus provisions for contingencies, so the profit target is set with expected float income in view. Surplus is the insurer's own capital, so its return is not credited against policyholders.

Implicitly. In other states, the filing may not break out an investment line. The insurer instead uses a target profit and contingency provision, a percentage of premium, that it considers adequate for the company's return, with the expected investment income already in its thinking. The regulator reviews the final rate for reasonableness without a formal investment credit. Which approach applies varies by state and by insurer, so the filing itself, or the state department of insurance, is the place to check. Our guide how car insurance rate approval works outlines the review process.

Researchers describe the same thing in theory. In her review of underwriting-cycle research, Temple University's Mary Weiss writes that a premium reflects expected losses discounted by an interest rate, plus underwriting expenses, plus profit or a risk charge, with taxes on investment income among the factors. In other words, the higher the discount rate, the lower the premium that is needed to fund the same expected claims. See the Weiss paper.

What the low-rate years did

The Federal Reserve cut the federal funds target to a range of 0 to 0.25 percent on March 16, 2020 and did not raise it until March 17, 2022, according to the Fed's open market page. In those two years, new money going into bonds earned very little. An insurer's portfolio does not reprice overnight, because it holds bonds bought in earlier years, so the effect on income was gradual.

The result for underwriting is a squeeze in principle: with less investment income cushioning results, the combined ratio an insurer needs in order to earn its target return is lower. In personal auto the low-rate years coincided with something else that dominated, which was a drop in driving and claim frequency in 2020 and a surge in claim costs afterward. Triple-I's industry overview shows net investment income for all property and casualty insurers of $56.1 billion in 2021, rising to $71.5 billion in 2022 and $91.8 billion in 2025. As a share of net premiums written ($715.7 billion in 2021 and $980.3 billion in 2025) that is about 7.8 percent in 2021 and about 9.4 percent in 2025. These are industry-wide figures for all lines, from NAIC data via S&P Global Market Intelligence, and the ratio is our arithmetic.

Why higher yields do not automatically cut prices

If float income is a cushion, then higher yields should lower prices. They sometimes do, at the margin, but several things work against a visible effect.

1. The sums are small next to claim trend. In the example above, moving yield from 1 to 4 percent is worth about $2.25 per $100 of premium. A claim-cost trend of 5 or 10 percent a year is worth $5 to $10 per $100 on the claims side. When costs trend faster than yields move, the cost trend wins.
2. The timing is wrong. Between 2022 and 2023, the Fed lifted rates from near zero to a peak of 5.25 to 5.50 percent (reached July 27, 2023). Over those years, the BLS auto insurance price index rose 14.32 percent in 2022 and 20.30 percent in 2023, according to a table in the NAIC's 2022/2023 Auto Insurance Database Report. Rates rose because repair, used-car and injury costs rose faster than float income. Our companion article on hard and soft markets: why car insurance prices move in cycles covers the pattern.
3. Insurers must rebuild surplus. After a run of losses an insurer's capital is thinner. Weiss describes how adverse loss shocks push up the ratio of premiums to surplus, which forces insurers to raise prices or write less. Investment income helps rebuild surplus, and a portion of it goes there rather than into lower rates.
4. Competition decides how much is passed on. Weiss describes a cash-flow underwriting hypothesis: when the interest rate margin widens, insurers may cut prices to gain market share and the assets to invest, then tighten when losses or rates turn. The effect is to pass float income to buyers through competition, not by formula, and only while the market is competitive.
5. Filing lag. A filing uses assumptions from when it was prepared, and rates may be in effect for a year or more. A jump in yields does not reach consumers until filings assume it. See from filing to your bill: the timeline of an auto rate increase.
6. Stocks can move the other way. Property and casualty insurers hold a large share of the industry's common stock. Falling equity markets can cut surplus even while interest income is high, and rising markets can raise it without any change in underwriting.

Surplus, solvency and the rating agencies

An insurer's capital, called surplus in statutory accounting, is the margin that lets it keep paying claims after a bad year. Regulators set minimum capital rules, and rating agencies assess the margin. AM Best rating reports describe a company's financial strength, and if an insurer fails, the state's guaranty fund covers claims up to statutory limits that vary by state.

Investment results matter here because a company with strong investment income has more room to absorb an underwriting loss and still add to surplus. This is one reason an insurer might price its auto line to a combined ratio slightly above 100 and still be solvent and profitable overall. It is also why sustained investment losses can force rate increases on a line that is otherwise earning its keep.

A rating or a guaranty fund is not a reason to pick or avoid a company by itself, but financial strength is part of what you are buying: a promise to pay a claim, possibly years from now.

How to read investment income in a statutory annual statement

Every U.S. insurer files an annual statement with its state regulator on a form designed by the NAIC. It is not written for consumers, but the income statement page is readable. Many state departments of insurance can supply an insurer's filing, and some insurers post their own. As an example of the layout, the 2024 annual statement of Safety Property and Casualty Insurance Company, posted on safetyinsurance.com, has a Statement of Income that runs in this order.

1. Underwriting income. Premiums earned (line 1), then losses incurred, loss adjustment expenses incurred, and other underwriting expenses incurred (lines 2 to 4). Net underwriting gain or loss (line 8) is premiums earned minus total underwriting deductions.
2. Investment income. Net investment income earned (line 9), which comes from a separate Exhibit of Net Investment Income, and net realized capital gains or losses (line 10). Their sum is the net investment gain or loss (line 11).
3. Other income, dividends, taxes. Then net income, followed by a capital and surplus account that begins with surplus as regards policyholders at the end of the prior year.

In that 2024 filing, net underwriting was a loss while net investment income earned was larger than the loss, so the company's pre-tax result was positive. That pattern, an underwriting loss covered by investment income, is common and not a warning sign by itself.

A short guide to reading one yourself:

1. Find the right legal entity. Insurance groups have many companies. The one that issues your policy is named on your declarations page, and its statement may differ from the group's.
2. Start with the two subtotals. Compare the net underwriting gain or loss with net investment income earned. If the first is negative and the second positive, the company is relying on float.
3. Separate investment income from capital gains. Net investment income earned is the recurring interest and dividends. Realized capital gains are lumpy and can be a one-year event.
4. Check the trend. Look at two or three years, not one. A single year can be distorted by a catastrophe, a reserve change, or a market move.
5. Look at surplus. The surplus line shows the capital cushion. A sharp fall deserves a look at the notes.
6. Compare with the NAIC's profitability report. The NAIC's profitability report, based on annual statement data, estimates profit on earned premium and return on net worth by state and line, and lists investment income as one component. It said private passenger auto was about 33 percent of total direct premiums earned in 2022. Our guide to What NAIC auto insurance data measures covers related data.

A rate filing is a different document from an annual statement. For help reading one, see How to read a car insurance rate filing on SERFF and how an actuary builds a statewide auto rate: a worked indication.

Common questions

If my insurer earns money on my premium, why is that not credited to me?

In explicit states, part of it is. Florida's statute directs regulators to consider the investment income expected from the premium and reserves when judging whether a rate is excessive. It is reflected in how the rate is calculated, not as a line on your bill. Income earned on the insurer's own surplus is not part of that credit in Florida.

Will falling interest rates raise my premium?

Not directly. Lower yields reduce a cushion, so an insurer that was just breaking even would want a better underwriting result, which can mean smaller discounts or larger increases than otherwise. But claim costs, not yields, have been the driver of recent price changes, and the effect of rates on premiums is slow and hard to isolate.

Does a high combined ratio mean the insurer is losing money?

Not necessarily. A combined ratio above 100 means an underwriting loss, but investment income may make up for it. Read the underwriting result and the investment result together. See combined ratio for a definition.

Where can I find an insurer's financial strength?

Start with its rating from an agency such as AM Best, and its annual statement from your state department of insurance. Your department can also explain what your state's guaranty fund covers.

Key takeaways

• Insurers invest premiums before claims are paid. For a short-tail line like auto the float is small, so investment income is a modest cushion, not a large source of lower prices.
• Some states, such as Florida, direct regulators to weigh investment income on premium and reserves in rate review; others handle it implicitly through a profit provision. Check the filing or your state's department.
• Higher yields do not automatically cut prices: claim-cost trends have been larger, filings lag, surplus must be rebuilt, and only competition passes income on.
• A statutory annual statement shows underwriting result and net investment income on separate lines. Read both, over several years, for the correct legal entity.