The price of liability limits: how much each step up really costs

Moving from a low set of liability limits to 100/300/100 usually raises the liability part of your premium by a modest fraction, not by the multiple the limits themselves imply. In a filed North Carolina rate table, tripling the per-accident bodily injury limit from $100,000 to $300,000 (and doubling the per-person limit) adds about a quarter to the bodily injury charge. The reason is that the limit only matters on the rare large claim, while most of the premium pays for ordinary claims that every limit covers.

This article walks up the ladder one step at a time, using a real approved factor table as the evidence, a hypothetical driver to put dollars on it, and a decision rule for choosing where to stop.

What you are actually buying with a limit

A liability limit is the most your insurer will pay for damage you cause to other people. It is written as three numbers, such as 100/300/100: the first is the bodily injury liability limit per injured person, the second is the bodily injury limit for everyone hurt in one accident, and the third is the property damage liability limit for what you damage. Our guide to what 25/50/25 means: split liability limits explained covers the notation in detail, and the liability limits decoder translates any set of numbers.

Two things about that purchase shape the price.

First, you are not buying a payment of that size. You are buying a promise to pay up to that amount if you cause a crash that needs it. In any given year, most policyholders who buy 100/300 never come near $300,000 of claims. The insurer prices the cost of the claims it expects to pay, and the expected payment from a high limit is small because large claims are rare.

Second, in most personal auto policies the insurer's duty to defend you in a lawsuit sits on top of the limit rather than reducing it. The cost of that defense is part of the base price at every limit level, which is another reason the price does not scale with the limit. The policy wording controls this, so read the "supplementary payments" section of yours.

A state's legal minimum is the floor, not a recommendation. The Insurance Information Institute (Triple-I) says in its auto insurance basics article that state-required minimums may not cover the costs of a serious accident. That article carries no publication date, so treat it as current guidance rather than a dated statistic.

Why the price curve flattens

Think of a liability limit as stacked layers of protection. The first layer, say the first $25,000 of an injury claim, gets used on a large share of all injury claims. The layer between $100,000 and $300,000 is used only on claims that are already severe. Insurers price each layer by how often it is likely to be reached and how much it will pay when it is.

Actuaries package this as an increased limit factor (ILF): a multiplier applied to the base liability premium for a chosen limit. The base limit has a factor of 1.00, and a higher limit has a larger factor. Because the upper layers are reached so rarely, each step up adds a smaller percentage than the step before it, even though the dollars of protection grow quickly. Our companion article on why doubling liability limits does not double the premium explains the actuarial logic in more depth.

There are limits to the flattening. The curve does not go flat; it just rises slowly, and the factors differ by state, insurer and coverage, so any one table is an illustration of the shape, not a price for your car.

A filed factor table: what North Carolina's rate bureau published

North Carolina is a useful example because its private passenger auto rates are filed by a bureau on behalf of member insurers and the factors are public. In a circular dated March 27, 2024, the North Carolina Rate Bureau told member companies that the Commissioner of Insurance had approved revised liability base rates and increased limit factors. They apply to policies effective on or after January 1, 2025, and were prompted by a law raising the state's minimum liability limits from 30/60/25 to 50/100/50.

The base for the bodily injury table is 50/100, so that limit carries a factor of 1.00. Here is a selection of the approved bodily injury factors:

Read the last row against the first. The 500/1,000 limit is ten times the protection of 50/100, per accident, and the filed factor is under twice the base. The same table shows the smaller steps clearly: going from 100/200 to 100/300 adds 2 points (1.24 to 1.26) for an extra $100,000 of per-accident protection. Raising the per-person limit does cost more, because the individual claim is where severe injuries land.

The property damage table in the same filing is flatter still. None of its factors, across limits from the base up to $1 million, is higher than 1.177. In plain terms, you can buy a very large property damage limit for a premium increase of well under a fifth of that coverage's base charge. That matters because property damage is the cheapest limit to raise, and the one most often left too low; see why property damage limits fall short in today's crashes.

The filing's base rates vary by territory, so a driver in one part of the state pays a different starting point than a driver in another. In the circular's Territory 110, for example, the bodily injury base rate for 50/100 is $217. The base rate is not what you pay, because driver, vehicle and other factors multiply it, which is why the next section uses a hypothetical driver rather than quoting any territory as a price.

One more caution: the North Carolina table starts at 50/100 because that is the state's new minimum. It does not include 25/50, and it would be wrong to treat 25/50 to 100/300 as the same percentage jump. A state with lower minimums files its own factors, and the jump from a lower base is typically a larger percentage, though the curve flattens the same way.

Putting dollars on the curve: a worked example

The numbers below are hypothetical. Say a driver's bodily injury premium at 50/100 is $400 a year after all other rating factors. We apply the North Carolina factors above to show the shape; your own quote will differ.

Now look at what each step buys, per accident:

• 50/100 to 100/300: $200,000 more protection per accident for about $9 a month.
• 100/300 to 250/500: $200,000 more per accident for about $11.67 a month more.
• 250/500 to 500/1,000: $500,000 more per accident for about $10 a month more.

The price of each additional $100,000 of protection falls as you climb: roughly $4.30 a month for each $100,000 in the first step, about $5.80 in the second, and about $2 in the third. The curve is not a straight line, and it is not perfectly smooth either, because the per-person limit moves along with the per-accident limit. If the premium were proportional to the limit, going from 50/100 to 500/1,000 would multiply the bodily injury charge by ten. Here it is multiplied by 1.91.

Add your property damage charge to the bodily injury figure and you have the liability total. An uninsured-motorist or collision charge is separate and not affected by the limit you pick, with one exception: in some states, uninsured and underinsured motorist limits are linked to liability limits, so raising one can raise the other. Ask your insurer which applies in your state.

Bodily injury versus property damage

The two kinds of limits behave differently, and the decision about each is separate.

Bodily injury. The per-person limit is the one that bites in a serious crash, because a single severely injured person can exceed it on their own. The per-accident limit caps the total across everyone hurt, so it matters when you have passengers in another car or several people in yours. If you carry 100/300, one person can claim up to $100,000 and all claimants together up to $300,000. A higher per-accident limit without a higher per-person limit does little for a single catastrophic injury.

Property damage. The limit pays for the other person's vehicle, plus anything else you hit: a fence, a storefront, a utility pole. A multi-car crash can consume it quickly. The NC factors show how little more it costs to raise this limit, so the usual pattern in a budget-conscious household is a low property damage limit sitting next to a bodily injury limit that is a reasonable fit. Raising property damage is the easiest improvement to price.

A combined single limit policy replaces the three numbers with one amount for any combination of injury and property damage in an accident. It is simpler and can be more flexible, though it also lets a large property claim use up the money meant for an injured person. See combined single limit vs split limits.

Umbrella eligibility changes the question

If you may ever want an umbrella policy, your auto limits may not be entirely your choice. Triple-I notes in its guide to umbrella liability policies that most insurers want about $250,000 of liability insurance on your auto policy (and about $300,000 on your homeowners policy). The page carries no date. Individual umbrella carriers set their own thresholds, so confirm the number with the one you are considering.

This changes the arithmetic. A household that stops at 100/300 and later wants an umbrella must raise auto limits first, usually at the same time it buys the umbrella. Triple-I's guide to how much coverage you need puts the price of an umbrella at typically $200 to $300 a year for a million dollars of coverage, and also notes there is no date on the figure. If the umbrella is a plausible purchase, price the higher underlying limits as part of the package, not as an isolated upgrade. The article on adding an umbrella policy to your auto bundle: what it requires covers the process.

A decision rule for choosing your limits

No rule can tell you your correct limit, but the pricing curve supports a way of thinking about it.

1. Start from what you have to lose. Add up the assets a plaintiff could reach (savings, home equity if your state allows it, non-exempt investments) and your income, since depending on state law a judgment can sometimes be collected from wages. The more you have, the higher the limit.
2. Get three quotes at once. Ask for your minimum, 100/300/100 and 250/500/100 (or your insurer's next tier) from the same insurer on the same day. The car insurance quote comparison worksheet helps you keep the three side by side.
3. Compute the monthly cost of each step. Subtract the lower quote from the higher and divide by 12, as in the worked example.
4. Buy the highest step whose added monthly cost you can carry without cutting a more urgent need. If a higher step costs the price of one takeout meal a month, the question answers itself. If it is a cost you would struggle to pay, a lapse would be worse than a lower limit; see when you can't afford car insurance: options before the policy lapses.
5. Revisit when your situation changes. Buying a home, a raise, a new teen driver, or a state raising its minimum are all reasons to re-run the three-quote comparison.

The How much car insurance do I need? and our guide on how much liability coverage do you need? go through the same logic with your numbers. For five different household profiles worked through the same way, see choosing liability limits for five different households.

The cost of going too low

Low limits are the cheapest part of the premium you can trim, and often the most expensive decision in a serious crash. If damages exceed your limit, the injured person can pursue you personally for the rest. The legal mechanics vary by state, and a licensed attorney is the right person to ask about exposure on your specific facts. Our article on the judgment-proof myth: what cheap limits expose after a crash explains why having little to take is not the protection many people think it is.

Compare the stakes with the premium. In the hypothetical table above, the step from 50/100 to 100/300 costs about $104 a year. A single crash with a $250,000 injury claim leaves a household with a 50/100 policy facing $200,000 beyond the $50,000 per-person limit, before any other costs. The numbers in this paragraph are illustrative only.

Common questions

Does raising my limits make my rate go up at renewal?

Raising limits raises the liability premium once, when the new limits take effect, by the ILF difference. It does not by itself change how your rate moves at later renewals. Your driving record, claims and the insurer's filed rates drive those changes. A higher limit also does not increase your deductible or reduce your collision payment.

Can I raise limits in the middle of a policy term?

Most insurers let you change liability limits mid-term, usually from the date you request it, with the premium adjusted for the remaining term. A change does not reach back to a crash that has already happened, so the day you ask is the day it counts. Ask for confirmation in writing or an updated declarations page.

Is 100/300/100 always the right target?

No. It is a common reference point, not a rule. A renter with few assets may find 50/100 adequate, a homeowner with a retirement account and a teen driver may want more, and your state's minimum may already be above where this article started. See 100/300/100 vs 250/500/100: what the extra limits buy for what the next step buys.

Do these North Carolina factors apply in my state?

No. They show the shape of the curve for one state's filed personal auto rates. Every state and insurer has its own factors, and some states have different rating rules altogether. Use the state car insurance requirements lookup for your state's minimums, and ask your insurer or your state insurance department how limit changes are priced where you live.

Key takeaways

• Premium rises much more slowly than limits: in a North Carolina filing approved for 2025, 500/1,000 bodily injury costs a factor of 1.91 against 1.00 for 50/100.
• Each step up buys more protection per dollar than the one before it, so the highest limit you can comfortably afford is usually better value than the lowest you can legally carry.
• Property damage limits are the cheapest to raise, and bodily injury per-person limits are where a severe crash does the most harm.
• If an umbrella policy is possible, price the higher underlying auto limits it requires as part of the same decision.
• Get three quotes at once, compute the monthly price of each step, and buy the highest one you can carry without risking a lapse.