Every figure in this article is traced to the primary sources listed under Sources.

Carry uninsured/underinsured motorist limits equal to your bodily injury liability limits. If you carry 100/300 liability coverage, choose 100/300 UM/UIM. That way, if an uninsured or underinsured driver injures you, your own policy can pay up to the same limits you carry to protect others. Check your policy and state rules.

Key Takeaway: UM/UIM coverage is liability insurance you buy for yourself. It responds when the at-fault driver cannot pay. Uninsured motorist coverage applies when the other driver has no liability insurance. Underinsured motorist coverage applies when the other driver has some insurance but not enough to cover your injuries. In 2023, 15.4% of U.S. motorists were uninsured, according to the Insurance Research Council. The rate ranged from 5.7% in Maine to 28.2% in Mississippi. A common rule of thumb is to match UM/UIM limits to your liability limits, but state requirements differ. Check your declarations page, confirm your state’s rules, and ask your insurer what it would cost to close the gap.

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How much uninsured motorist coverage do I need?

A common rule of thumb is to carry uninsured/underinsured motorist limits equal to your bodily injury liability limits. If you carry 100/300 liability coverage, consider 100/300 UM/UIM. That rule is also useful when you decide how much liability car insurance you need. The point is to make your own policy stand in for the at-fault driver’s missing or insufficient coverage.

This is a recommendation, not a legal requirement in every state. Some states require UM/UIM limits to match liability limits; others allow lower UM/UIM limits. The Texas Department of Insurance, for example, suggests adding enough coverage to replace your vehicle, which is a related but not identical rule of thumb. Your state’s insurance department is the authoritative source for what your state requires.

15.4%U.S. motorists uninsured in 2023, according to the NAIC.
5.7%Lowest state uninsured rate in the NAIC data: Maine.
28.2%Highest state uninsured rate in the NAIC data: Mississippi.

How do UM/UIM limits work?

UM/UIM limits are usually written as two numbers, such as 50/100. The first number is the most the policy will pay for one person’s bodily injury in a single accident. The second number is the most it will pay for all bodily injuries in that accident.

Suppose a driver carries 50/100 UM/UIM limits and is hit by an uninsured driver. The driver and one passenger are injured. The driver’s medical bills are $60,000. The passenger’s bills are $30,000. The UM coverage could pay up to $50,000 for the driver and up to $50,000 for the passenger, but no more than $100,000 total for the accident. If the driver had chosen 100/300 limits instead, the coverage could pay up to $100,000 for the driver and up to $100,000 for the passenger, with a $300,000 total cap. This example is hypothetical and uses round numbers; actual claims depend on the policy, the state, and the facts of the accident.

Now suppose the at-fault driver is not uninsured but underinsured. The at-fault driver carries 25/50 liability limits. The injured driver has 50/100 UIM limits. The injured driver’s damages are $80,000. The at-fault driver’s liability policy pays its $25,000 per-person limit. The injured driver’s UIM coverage may then pay the difference between the at-fault driver’s limit and the injured driver’s UIM limit, subject to the policy’s terms. Under a “difference in limits” UIM policy, the maximum UIM payment would be $25,000 ($50,000 UIM limit minus $25,000 already paid by the at-fault driver). Under an “excess” UIM policy, the UIM coverage could pay above the at-fault driver’s payment, up to the UIM limit. This example is also hypothetical and illustrates why the type of UIM coverage matters. Idaho’s insurance disclosure materials describe both “difference in limits” and “excess” UIM structures.

Practical note: A hit-and-run accident can still trigger UM coverage even when the other driver is never identified, depending on your policy and state rules.

What is stacking, and does it apply to my policy?

Stacking means combining the UM/UIM limits assigned to multiple vehicles on the same policy, or under multiple policies, to increase the total coverage available after an accident. If you have two cars, each with $50,000 of UM coverage, stacking could in theory make up to $100,000 available, depending on state law and policy terms.

Stacking is not automatic nationwide. About half of U.S. states allow stacking by default; others prohibit it or allow it only with a specific endorsement or waiver. Pennsylvania law, for example, permits a named insured to waive stacked limits by signing a written rejection form, and the statute describes stacking as the default when multiple vehicles are insured. Kansas law prohibits stacking of uninsured and underinsured motorist coverages. The NAIC does not impose a uniform national stacking rule.

What to do: Ask your insurer or agent whether your policy stacks UM/UIM limits across vehicles, whether stacking costs extra, and whether you have signed any waiver. The answer can materially change the coverage available after a serious accident.

Do state rules require UM/UIM to match liability limits?

UM/UIM rules are state-specific. Some states require UM/UIM coverage, some require only uninsured motorist bodily injury coverage, and some do not require it at all. Some states require UM/UIM limits to match your liability limits, while others allow lower limits. Because the rules vary, the amount you need is not a single national number. Start with your state’s minimum, then compare it with your liability limits and your financial exposure.

State rule
New Hampshire
RSA 264:15 says UM coverage “shall automatically be equal in amounts and limits to the liability coverage elected” when liability coverage above the minimum is bought.
If you buy higher liability limits in New Hampshire, check that your UM coverage matches them.
State rule
Kansas
K.S.A. 40-284 requires uninsured motorist coverage to include an underinsured motorist provision with “coverage limits equal to the limits of liability” of the UM coverage.
Kansas drivers should confirm how the matching rule applies to their policy and limits.

Compare coverage limits with the same deductibles

If you are shopping, use the same limits and deductibles so the price difference reflects coverage, not a lower benefit.

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Who is most affected by uninsured drivers?

Drivers in states with high uninsured rates face greater exposure. The NAIC’s 2023 data show rates above 20% in several states, including Mississippi at 28.2%. Drivers who carry only the legal minimum liability limits, drivers without collision coverage, and drivers without medical payments or personal injury protection also rely more heavily on UM/UIM after an accident with an uninsured or underinsured driver. Drivers who have significant assets or depend on their vehicle for work may need limits above the state minimum to protect themselves.

What should drivers do now?

Open your auto policy and find the declarations page. Compare your UM/UIM limits with your bodily injury liability limits. Then take these steps.

Find your UM/UIM limits
You cannot close a gap you cannot see.
Look for uninsured motorist bodily injury, underinsured motorist bodily injury, and uninsured motorist property damage. Write down the limits shown.
Compare them with your liability limits
The two sets of limits should usually match.
If your UM/UIM limits are lower than your liability limits, ask your insurer or agent how much it would cost to raise them to the same level.
Ask about stacking
Stacking rules can change the total coverage available.
Ask whether your policy stacks UM/UIM limits across vehicles, whether stacking costs extra, and whether you have signed a waiver.
Ask about your state’s matching rule
State law may already require matching limits.
Ask specifically whether your state requires UM/UIM limits to match your liability limits.
Report an uninsured-driver accident promptly
Deadlines and documentation can affect the claim.
Report the accident to the police within the time your state requires. Notify your insurer promptly. Document the scene, get medical attention, and keep all records.
Confirm the claim in writing
A written record reduces confusion.
Ask your insurer to confirm in writing that the claim is being handled under your UM/UIM coverage.
Use your state insurance department
It is the official source for complaints and rules.
If you have questions about state rules or a claim dispute, contact your state insurance department.

What the data does not tell you

Limits of the data: The NAIC figure is a national average. It does not tell you the uninsured rate in your ZIP code, your age group, or your type of vehicle. It also does not tell you how many underinsured drivers are on the road. Your own risk depends on where you drive, how much you drive, and the coverage you choose. The example limits in this article are illustrative. They are not a quote, and they do not predict what any insurer would charge or pay. Stacking and UIM structures add further variation that a single national average cannot capture.

Frequently Asked Questions About Uninsured Motorist Coverage

Do I need uninsured motorist coverage?

UM/UIM is not mandatory in every state. Some states require UM/UIM, some require only uninsured motorist bodily injury coverage, and some do not require it at all. Check your policy and your state insurance department.

Does uninsured motorist coverage cover hit-and-run accidents?

Yes. If you are injured in a hit-and-run accident, UM coverage can respond even though the other driver is never identified, depending on your policy and state rules.

Should my UM/UIM limits match my liability limits?

A common rule of thumb is to carry UM/UIM limits equal to your bodily injury liability limits. If you carry 100/300 liability coverage, consider 100/300 UM/UIM. State rules vary, and some states require the limits to match while others do not. Confirm with your insurer or state insurance department.

What is stacking of UM/UIM coverage?

Stacking means combining UM/UIM limits across multiple vehicles or policies. About half of U.S. states allow stacking by default; others prohibit it or allow it only with an endorsement or waiver. Ask your insurer whether your policy stacks and whether a waiver applies.

The bottom line

A common rule of thumb is to carry UM/UIM limits equal to your liability limits. If you have 100/300 liability coverage, consider 100/300 UM/UIM. Check your policy, ask whether stacking applies, confirm your state’s rules, and ask your insurer what it would cost to close the gap.

Doing nothing leaves you exposed to the uninsured and underinsured drivers you share the road with every day.

How We Verified This

We reviewed the NAIC’s uninsured motorist topic page, last updated July 30, 2025, which provides the 2023 uninsured rate from the Insurance Research Council and explains the difference between UM and UIM coverage. We reviewed New Hampshire RSA 264:15 through the state’s official legislative record and Kansas K.S.A. 40-284 through the Kansas Legislature. We reviewed Idaho Department of Insurance disclosure materials for the difference between “difference in limits” and “excess” UIM coverage. We reviewed Pennsylvania’s stacking statute (75 Pa.C.S. § 1738) and related legislative materials for the stacking waiver framework. We reviewed the Texas Department of Insurance guidance on adding enough coverage to replace the vehicle. We could not verify every state’s minimum UM/UIM requirement or every state’s stacking rule in this review.

Reviewed against the cited sources and approved by the editor before publication.

Disclaimer: This article is for informational purposes only and is not professional insurance, legal or financial advice. Rates, rules and deadlines vary by insurer, state and driver, and can change. Confirm details with a licensed agent, your insurer or your state department of insurance before making a coverage decision.

Sources

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