Uninsured and underinsured motorist coverage, usually written as UM/UIM, pays you through your own auto insurance policy when the driver who caused your accident has no insurance or not enough of it. About one in seven drivers on U.S. roads — 15.4 percent — carry no insurance at all, according to the Insurance Research Council’s most recent study.1Insurance Information Institute. Facts + Statistics: Uninsured Motorists UM/UIM shifts that risk from your savings to your insurer, so a stranger’s lack of coverage doesn’t become your financial problem.
The Four Pieces of UM/UIM Coverage
UM/UIM is not a single coverage. It splits into four components, and not all of them exist in every state.
Uninsured Motorist Bodily Injury (UMBI) covers medical expenses, lost income, and pain and suffering for you and your passengers after a crash caused by a driver with no insurance. The compensable losses are broader than many policyholders realize: beyond hospital bills and rehabilitation, UMBI typically covers non-economic harm like chronic pain, emotional distress, and reduced quality of life, up to the limit on your declarations page. Payouts track documented medical records and financial losses, not a flat figure.
Uninsured Motorist Property Damage (UMPD) pays to repair or replace your vehicle when the at-fault driver has no insurance. It exists in roughly half the states, and even where it does, it often won’t cover hit-and-run damage if the other driver is never identified. If you already carry collision coverage, UMPD is largely redundant, because collision pays for accident damage regardless of fault. Where UMPD earns its keep is for drivers who skip collision to save on premiums; it fills the gap specifically for damage from an uninsured driver, often with a lower deductible or none at all.
Underinsured Motorist Bodily Injury (UIMBI) kicks in when the other driver has insurance but not enough. If their liability limit is $25,000 and your medical bills reach $75,000, UIMBI covers some or all of that $50,000 shortfall. How much, exactly, depends on your state’s calculation method, which matters enough to get its own section below. This is arguably the most valuable piece of the whole package, because even insured drivers frequently carry only the bare minimum liability limits.
Underinsured Motorist Property Damage (UIMPD) does the same job for vehicle damage, bridging the gap when the other driver’s property damage limit falls short of your repair or replacement costs. Availability varies by state, and collision coverage often makes it unnecessary.
When UM/UIM Actually Pays Out
The most straightforward trigger is a collision with a driver whose policy has lapsed or who never bought one. Fines and license suspensions exist in every state, but millions of people drive uninsured anyway, and their personal assets are rarely enough to cover serious injuries. UM lets you file directly with your own insurer instead of chasing a judgment you’d probably never collect.
Hit-and-run accidents are the second common trigger. When the other driver flees and is never identified, most states treat that unidentified driver as uninsured, which brings your UM coverage into play. Watch for one trap: some states require physical contact between the vehicles for UM to apply in a hit-and-run. That rule can exclude sideswipe-and-flee situations where another driver forces you off the road without touching your car. Check your policy language on this point before you need it.
A fact that catches many policyholders off guard: UM/UIM generally protects you even when you aren’t in your car. If an uninsured driver hits you while you’re walking, jogging, or cycling, your own auto policy’s UMBI coverage typically applies, and the same protection extends to household family members covered under your policy. For anyone who spends time near traffic on foot or on a bike, that stretches the value of the coverage well beyond driving.
UM can also save a claim when the at-fault driver’s insurer goes bankrupt before paying. Most states treat that driver as effectively uninsured in those circumstances, as long as the insolvency happens within a set period after the accident, often one to two years. State guaranty associations may provide some recovery too, but UM coverage is faster and more reliable.
How Much a UIM Claim Actually Pays
This is where most policyholders get an unpleasant surprise. When a UIM claim is approved, the amount you collect depends on which of two calculation methods your state uses, and the difference can run into tens of thousands of dollars.
The Offset Method
Under the offset approach, your insurer subtracts the at-fault driver’s liability limit from your UIM limit, and whatever remains is the most your UIM policy will pay. If you carry $100,000 in UIM coverage and the at-fault driver has $50,000 in liability, your UIM insurer’s maximum exposure is $50,000. Your total recovery from both insurers combined caps at $100,000, which is your own UIM limit.
The Excess Method
Under the excess approach, the at-fault driver’s payment reduces your total damages rather than your policy limit. Your full UIM limit stays available on top of whatever the other driver’s insurer paid. Using the same numbers, $100,000 in UIM coverage and $50,000 from the at-fault driver, you could recover up to $150,000 total if your damages justify it. This is the more common of the two methods.
Why the Difference Matters to You
Picture a real scenario: you carry $50,000 in UIM coverage and the at-fault driver has $25,000 in liability. Your medical bills total $70,000. Under the offset method, your UIM insurer pays at most $25,000 (the difference between the two limits), leaving you $20,000 short. Under the excess method, your UIM insurer can pay up to $45,000 ($70,000 in damages minus the $25,000 already received), leaving you fully covered. If you live in an offset state, the practical takeaway is to buy UIM limits significantly higher than the minimum liability limits in your state. Otherwise your UIM coverage may be worth little or nothing.
Get Your Insurer’s Consent Before You Settle
This is the single most expensive mistake people make with UIM claims, and most drivers have never heard of the rule. Before you accept a settlement from the at-fault driver’s insurer, you almost certainly need written permission from your own UIM carrier. Settle without it and you risk forfeiting your entire UIM claim.
The reason is straightforward. Once you sign a release with the at-fault driver’s insurer, your UIM carrier loses its right to pursue that driver for reimbursement (subrogation). Courts have consistently held that settling without consent bars you from collecting UIM benefits afterward, even if the settlement amount itself was reasonable. In some states, a UIM insurer that refuses consent must pay you the amount of the at-fault driver’s settlement offer within a set period, so you aren’t left waiting indefinitely.
The practical move: when you receive a settlement offer from the other driver’s carrier, send a copy to your own insurer by certified mail before you sign anything. That one step protects tens of thousands of dollars in UIM benefits that would otherwise disappear.
Stacking Coverage Across Vehicles
If you insure more than one vehicle, you may be able to combine, or “stack,” your UM/UIM limits across them, raising the amount available for a single accident.
Intra-policy stacking lets you add up the UM/UIM limits for every vehicle on one policy. Three cars each carrying $50,000 in UM coverage would produce $150,000 in stacked coverage for one accident. The premium bump is usually modest relative to the coverage boost.
Inter-policy stacking combines limits across separate policies, such as yours and a spouse’s or parent’s policy if you live in the same household and qualify as an insured under both. It’s less commonly permitted than intra-policy stacking.
Many insurers include policy language that prohibits stacking. Whether those clauses are enforceable depends entirely on your state. Some have banned anti-stacking provisions; others allow them. If stacking is important to you, read the declarations page and endorsements carefully before you buy, and ask your agent directly whether stacking is available in your state.
Can You Skip It?
About 20 states and the District of Columbia require drivers to carry UM/UIM coverage on every auto policy. In those states, insurers cannot legally issue a policy without at least the minimum required limits, which often mirror the state’s minimum liability requirements.
In the remaining states, insurers typically must offer UM/UIM coverage but may let the customer decline it. The opt-out process isn’t casual. Most states require a formal written rejection stating that the driver understands the risks. If the insurer fails to obtain that signed waiver, courts in many states have held that UM/UIM coverage is automatically included at the policy’s liability limits, regardless of what the premium reflects. That rule exists to stop insurers from quietly stripping coverage without informed consent.
Drivers in no-fault states sometimes assume UM/UIM is unnecessary because personal injury protection (PIP) already covers medical bills regardless of fault. PIP pays only up to its own limit and generally only for certain economic losses, not pain and suffering. UM/UIM fills the gap above PIP and covers the non-economic losses PIP ignores, which is why regulators in no-fault states still recommend carrying it.
Filing a UM or UIM Claim
The claim runs through your own insurer rather than the other driver’s, but it still demands careful documentation and attention to deadlines.
- Report the accident to police immediately. The report documents the other driver’s insurance status (or absence of it) and establishes the basic facts. Many policies require a police report as a condition of UM coverage, especially for hit-and-run claims.
- Notify your insurer promptly. Your policy likely has a notice deadline, sometimes as short as 30 days. Late notification can give the insurer grounds to deny the claim. When you call, specifically say you’re making a UM or UIM claim so the right process starts.
- Gather documentation. Medical records, repair estimates, wage statements from your employer, and receipts for out-of-pocket costs all support the claim. Documented losses get paid; undocumented ones don’t.
- For UIM claims, get written consent before settling with the other driver’s insurer. Skipping this can kill the UIM claim entirely.
- Negotiate or arbitrate. Most UM/UIM policies include a binding arbitration clause for disputes over the amount owed. If you and your insurer can’t agree, the claim goes to an arbitrator rather than a courtroom. Arbitration is generally faster and cheaper than a lawsuit, but the decision is usually final.
Filing deadlines vary significantly by state. Some tie the deadline to the standard personal injury statute of limitations (often two to three years); others impose a separate deadline specific to UM/UIM claims. Missing one, even by a day, can permanently bar the claim, so verify the applicable time limits in your state as soon as possible after an accident.
What It Costs
UM/UIM is among the cheapest additions to a standard auto policy relative to the protection it provides. For standard limits matching most states’ minimum liability requirements, annual premiums typically run between $50 and $75. Upgrading to higher limits, such as $100,000/$300,000, adds roughly $20 to $40 per year. Rates vary substantially between carriers, sometimes by 30 to 50 percent for identical coverage, so shopping around pays off here as much as on any other coverage line.1Insurance Information Institute. Facts + Statistics: Uninsured Motorists