When the at-fault driver does not carry enough insurance, you first collect up to their policy limit from their insurer. After that limit runs out, your own Underinsured Motorist (UIM) coverage pays the remaining bills up to your UIM limit. If you do not carry UIM, you pay the leftover costs yourself or sue the at-fault driver in court to recover the gap. Your collision coverage can still repair your car regardless of the other driver’s limits, minus your deductible.
A short example makes this clear. Say your injuries and repairs total $75,000, and the at-fault driver carries only a $25,000 limit. Their insurer pays $25,000. If you hold $100,000 in UIM coverage, your own insurer steps in to cover the remaining $50,000. Without UIM, you absorb that $50,000 loss or chase the driver for it in court, where collection is often slow and uncertain.
The exact result depends on three factors: whether you carry UIM coverage, the limits on your policy, and how your state calculates the payout. This guide explains each piece, walks through real numbers, and lists the steps that protect your right to recover money.
Why So Many At-Fault Drivers Carry Too Little Insurance
Underinsured drivers are common, and the problem is growing. The Insurance Research Council reported that one in three drivers, 33.4 percent, were either uninsured or underinsured in 2023, a 10 percentage point increase in the combined rate since 2017. Nationally, more than one in seven drivers, 15.4 percent, were fully uninsured in 2023.
State minimum limits explain much of the gap. Many drivers buy only the lowest legal coverage, which often falls short of real crash costs. Several states recognized this and raised their floors. California’s minimum liability limits increased from 15/30/5 to 30/60/15, the first adjustment since 1967, and North Carolina raised its minimums to 50/100/50, giving it the highest required property damage minimum in the country at $50,000 per accident. Higher floors help, but a single serious injury can still pass any minimum limit quickly.
The math behind the gap is plain. A driver who carries a $25,000 bodily injury limit cannot cover a hospital stay, surgery, and weeks of lost wages that reach $80,000 or more. The updated state minimums raise the floor, yet they do not erase the problem, since modern medical and repair costs keep climbing. A driver who follows the law to the letter can still leave you well short of whole.
What Is Underinsured Motorist Coverage?
Underinsured Motorist (UIM) coverage protects you when the at-fault driver has insurance but not enough to pay for your injuries. The other driver’s liability insurance pays first, up to its limit. Then UIM steps in to cover the remaining personal injury costs, such as medical bills and lost income, up to the limit you bought.
UIM differs from its close cousin, Uninsured Motorist (UM) coverage. UM applies when the at-fault driver has no insurance at all. UIM applies when the driver has a policy that is simply too small. Insurers usually sell the two together as UM/UIM.
| Coverage | When It Applies | What It Pays |
| Underinsured Motorist (UIM) | At-fault driver has insurance, but limits are too low | The gap above their limit, up to your UIM limit |
| Uninsured Motorist (UM) | At-fault driver has no insurance | Costs the at-fault driver should have paid |
| Liability | You cause damage to others | Other people’s injuries and property, never your own |
| Collision | Any crash, regardless of fault | Repairs to your own car, minus deductible |
UIM mostly covers bodily injury. For vehicle damage left unpaid by a low-limit driver, your collision coverage usually handles repairs. Our guides on collision car insurance and full coverage car insurance explain how these layers work together.
How Does Underinsured Motorist Coverage Pay Out?
UIM follows a clear order. Knowing the steps shows you exactly when it applies.
- A crash happens and you are not at fault. The other driver caused the accident.
- Their insurer pays first. The at-fault driver’s liability coverage pays up to its limit.
- Their limit runs out. Your injuries and losses exceed what their policy covers.
- Your UIM coverage activates. Your insurer pays the remaining bills, up to your UIM limit.
- A gap may remain. If your costs pass your UIM limit too, you can pursue the driver for the rest.
UIM only activates after the at-fault driver’s limits are exhausted. You cannot use it as a first source of payment, and you must usually prove the other driver’s coverage fell short before your insurer pays.
The dollar layers become clearer with a few examples. The table below shows how a $100,000 UIM limit responds to crashes of different sizes in an offset state, where your UIM fills the gap up to your limit.
| Your Total Costs | At-Fault Driver Limit | UIM Pays | Remaining Gap You Cover |
| $40,000 | $25,000 | $15,000 | $0 |
| $75,000 | $25,000 | $50,000 | $0 |
| $130,000 | $25,000 | $75,000 | $30,000 |
| $90,000 | $50,000 | $40,000 | $0 |
The third row shows the limit of any UIM policy. Once your costs pass your own UIM limit, a gap reopens, and you must pursue the at-fault driver for the difference. Setting a higher UIM limit shrinks the odds of ever facing that leftover gap.
Does Your State Use Offset or Excess Rules?
How your state calculates the payout changes your total recovery, sometimes by tens of thousands of dollars. Two systems exist, and most drivers never learn the difference until they file a claim.
In offset states, also called gap states, your UIM coverage fills only the space between the at-fault driver’s limit and your own UIM limit. In excess states, also called add-on states, your full UIM limit sits on top of whatever the at-fault driver pays.
| State Type | At-Fault Driver Pays | Your UIM Limit | What You Collect Total |
| Offset (gap) state | $50,000 | $100,000 | $100,000 |
| Excess (add-on) state | $50,000 | $100,000 | $150,000 |
The numbers come from the same crash, yet the excess state pays $50,000 more. Policy language and state law decide which rule applies, so you should not assume your UIM limit automatically stacks on top of the other driver’s payment. Ask your agent which method your state uses before you set your limits.
What If You Do Not Carry UIM Coverage?
Without UIM, you lose your built-in safety net. Twenty states and the District of Columbia require uninsured motorist insurance, and 14 require UIM, which means many drivers in the remaining states skip it. If you fall in that group, two options remain.
- Pay the remaining costs yourself. You cover medical bills and repairs that the at-fault driver’s limit did not reach.
- Sue the at-fault driver. You take the driver to court to recover the gap. A judgment gives you a legal claim against their wages or assets.
Winning a lawsuit does not guarantee payment. A driver who could only afford a minimum policy often lacks the money or assets to satisfy a large judgment. That reality is why insurance professionals treat UIM as a defensive must-have rather than an optional extra. Our guide on how to sue a car insurance company without a lawyer covers the broader dispute process, and our explainer on what happens when a claim exceeds insurance limits digs deeper into recovery options when the bills run past coverage.
How Much UIM Coverage Should You Carry?
Your UIM limit should reflect the cost of a serious injury, not the state minimum. Medical bills, surgery, and months of lost income can pass $100,000 fast. Many drivers match their UIM limit to their liability limit so both move together.
Drivers with significant assets, such as a home or savings, often add an umbrella policy for an extra layer above auto limits. Our guide on umbrella insurance for car owners explains how that coverage extends protection beyond a standard policy.
Cost rarely blocks the decision. UM/UIM is one of the cheaper additions to an auto policy because it pays only after another insurer pays first. The protection it provides in a severe crash far outweighs the small monthly premium for most drivers.
A simple way to choose a limit is to picture the worst realistic crash, not the average fender bender. Add up what a hospital stay, rehabilitation, and several months without income would cost you, then set your UIM limit to match. Drivers who carry only the state minimum often discover, too late, that their own protection mirrors the same low ceiling that left the at-fault driver underinsured in the first place.
Does a No-Fault State Change the Answer?
No-fault rules affect how medical bills get paid right after a crash, not whether the at-fault driver carried enough coverage. In a no-fault state, your Personal Injury Protection pays your initial medical costs regardless of fault. For serious injuries that pass the state’s threshold, you can still step outside the no-fault system and pursue the at-fault driver, where UIM again becomes the backstop.
Property damage usually sits outside no-fault rules entirely and follows standard fault-based recovery. Our article on what a no-fault state means for car insurance clears up where these rules apply.
What Steps Should You Take After the Crash?
Acting in the right order protects both your health claim and your right to recover the gap.
- Get medical care and document injuries. Your records set the value of any UIM claim.
- File a police report. An official report establishes fault and the facts of the crash.
- Identify the at-fault driver’s coverage. Confirm their insurer and policy limit so you know the size of the gap.
- Notify your own insurer. Tell them you may file a UIM claim, since many policies set strict notice deadlines.
- Keep every bill and estimate. Medical statements, repair estimates, and wage-loss proof support your claim.
- Be careful before you settle. Accepting a quick offer from the at-fault driver’s insurer can affect your UIM rights in some states.
When you deal with adjusters, stay organized and document each call. Our guide on how to deal with an insurance adjuster after a car accident shows how to present your claim and avoid a lowball offer, and our explainer on rejecting a settlement offer covers your options when the first number is too low.
Frequently Asked Questions
A UIM claim for a crash you did not cause is a not-at-fault claim, so it should not raise your rates the way an at-fault accident would. Some insurers still apply a small surcharge after any claim, so ask your carrier first. The financial protection from a serious-injury claim usually outweighs a minor premium change.
UIM mainly covers bodily injury, such as medical bills and lost income. For vehicle damage the at-fault driver’s limit did not cover, your collision coverage typically handles repairs, minus your deductible. Some states also sell underinsured motorist property damage as a separate add-on.
Uninsured motorist coverage applies when the at-fault driver has no insurance at all. Underinsured motorist coverage applies when the driver has a policy, but the limits are too low to cover your costs. Insurers usually sell both together as UM/UIM.
Yes. You can sue the driver in court for the amount their insurance did not cover. A judgment gives you a legal claim against their income or assets, though a driver with a minimum policy may lack the funds to pay it. Many people use UIM first and pursue the driver only for any remaining gap.
It depends on your state. Twenty states and the District of Columbia require uninsured motorist coverage, and 14 require underinsured motorist coverage. Where it is optional, insurers must usually offer it, and you can add it in writing. Check your state rules or ask a licensed agent.
Match your UIM limit to the cost of a serious injury, not the state minimum, since medical bills can pass $100,000 quickly. Many drivers set UIM equal to their liability limit. Those with substantial assets often add an umbrella policy for protection above standard limits.
The Bottom Line
When the at-fault driver does not carry enough insurance, you collect their limit first, then your own UIM coverage pays the gap up to your limit. Without UIM, you absorb the leftover costs or sue the driver, where payment is far from certain. Your state’s offset or excess rules decide how much your UIM limit adds, and your collision coverage repairs your car regardless of the other driver’s limits. Carrying enough UM/UIM is the clearest way to protect yourself from a driver who cannot pay.
Insurance rules and coverage availability vary by state and by carrier, and serious-injury claims can involve legal questions beyond the scope of any single article. Always confirm your specific policy terms with a licensed agent or your state insurance department, and consult a qualified attorney for advice on a major claim. This article is for general information and does not replace professional or legal advice.
If you want to compare UM/UIM, liability, and collision options side by side, Alias Insurance lets you gather free quotes from leading U.S. providers in one place so you can set limits that match the real cost of a crash.
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