Uninsured and Underinsured Motorist Coverage, Explained

Quick answer: Underinsured motorist coverage is auto insurance that can help pay injury-related losses when an at-fault driver has liability insurance, but not enough to cover your damages.

It may cover medical bills, lost wages, and pain and suffering, depending on state law and policy terms. Check your policy and state insurance department before relying on coverage.

underinsured motorist coverage is insurance that can pay your covered injury losses when an at-fault driver’s liability limits are too low to cover the claim.

The at-fault driver’s insurer usually pays first; your UIM insurer may pay next, up to your policy limits and state offset rules.

It does not automatically cover every shortfall, pain claim, or vehicle damage; property damage requires separate coverage where available.

A claimant must document fault, the other driver’s limits, medical bills, lost wages, ongoing care needs, and prior insurance payments.

Because availability, stacking, consent-to-settle rules, and offsets vary by state and policy, check the state department of insurance and the NAIC’s consumer resources.

If Medicare, Medicaid, or a health plan paid bills, verify reimbursement duties with CMS or the plan before settling.

What underinsured motorist coverage pays

Underinsured motorist coverage, often called UIM, can pay when an at-fault driver has liability insurance but not enough to cover the injured person’s legally recoverable damages.

It is a first-party claim against the injured person’s own auto insurer, but the at-fault driver’s liability insurer usually pays first.

UIM does not automatically pay the policy limit. The claimant must prove fault, covered damages, the at-fault driver’s available bodily injury liability limits, and compliance with the UIM policy’s notice and consent-to-settle rules.

Item	How UIM typically works
Who pays first	The at-fault driver’s bodily injury liability insurer generally pays up to its policy limit before UIM applies.
What UIM may pay	Unpaid bodily injury damages such as medical bills, lost income, pain and suffering, and future care, subject to the policy and state law.
What it usually does not pay	Vehicle damage, routine deductibles, or losses above the UIM limit unless another coverage applies.
State variation	Rules on offset, stacking, rejection forms, and settlement consent vary by state; check the state department of insurance or NAIC consumer materials.

Example: if proven bodily injury damages are $100,000 and the at-fault driver has $25,000 in bodily injury liability coverage, that $25,000 is normally paid first. A $100,000 UIM limit may not mean another $100,000 is available.

In many policies, the UIM carrier receives an offset for the at-fault driver’s payment. In the example above, the maximum UIM payment could be $75,000, making total insurance payments $100,000.

Some states and policy forms treat limits differently, so the declarations page and state law matter.

• Proof of liability: police report, crash photos, witness statements, citations, and any comparative-fault evidence.
• Proof of insurance exhaustion: the at-fault insurer’s declarations page or written limits disclosure, settlement release, and payment confirmation.
• Proof of damages: medical records, itemized bills, wage records, disability notes, future-care opinions, and out-of-pocket receipts.
• Proof of required notices: timely UIM notice, insurer consent before settling with the at-fault driver, and any arbitration demand required by the policy.

Medical liens can reduce the claimant’s net recovery. Medicare, Medicaid, ERISA health plans, hospitals, and workers’ compensation carriers may assert repayment rights.

For Medicare conditional payments, the primary source is the Centers for Medicare & Medicaid Services, Medicare Secondary Payer rules.

Caution: Do not sign a release with the at-fault driver or accept a liability-limits settlement without checking the UIM policy. Some policies require written consent, and violating that condition can jeopardize UIM benefits.

How underinsured coverage differs from uninsured coverage

Underinsured motorist coverage and uninsured motorist coverage both protect an injured person when the at-fault driver cannot fully pay.

The key difference is whether the other driver has no usable liability insurance or has liability insurance that is too low.

Uninsured motorist coverage, often called UM, generally applies when the at-fault driver has no auto liability policy, cannot be identified in a hit-and-run, or has coverage denied by the insurer.

Underinsured motorist coverage, often called UIM, generally applies after the at-fault driver’s liability limits are exhausted.

Coverage type	Typical trigger	Who usually pays first	What it may cover
Uninsured motorist	At-fault driver has no collectible liability insurance or is an unidentified hit-and-run driver	The injured person’s own UM insurer, subject to the policy and state law	Bodily injury damages; property damage only if the policy and state allow it
Underinsured motorist	At-fault driver has liability insurance, but the limits are not enough to cover the proven damages	The at-fault driver’s liability insurer first, then the injured person’s UIM insurer if conditions are met	Damages above the at-fault driver’s paid limits, up to the UIM limit and subject to offsets

The National Association of Insurance Commissioners describes UM and UIM as coverages that pay for losses caused by drivers who lack insurance or lack enough insurance.

Exact availability, required offers, rejection forms, stacking rules, and property-damage treatment vary by state.

A claimant should check the state department of insurance for the state where the policy was issued and the crash occurred. State rules can control whether UM/UIM is mandatory, optional, waivable, or limited by statutory language.

• For UM: document that the other driver had no valid insurance, fled and could not be identified, or had coverage denied. Helpful records include the crash report, insurer denial letter, witness information, and hit-and-run police documentation.
• For UIM: document the at-fault driver’s liability limits, the amount paid by that insurer, medical bills, lost wages, and evidence that damages exceed the available liability coverage.
• For both: preserve medical records, treatment dates, repair estimates, wage records, photos, and communications with insurers.

Medicare, Medicaid, health insurers, and medical providers may have reimbursement or lien rights against an injury settlement.

For Medicare coordination and recovery rules, consult the Centers for Medicare & Medicaid Services, not a general article.

Caution: do not settle with the at-fault driver’s insurer or sign a release before checking the UIM policy’s consent-to-settle rules.

Some policies require the UIM insurer’s permission first, and failing to follow the policy can jeopardize benefits.

Who pays first after a crash

Underinsured motorist coverage usually does not pay first. It is a backstop that may apply after the at-fault driver’s liability insurance is identified, paid, or shown to be too small for the injured person’s covered losses.

The exact order depends on state law, policy wording, and the type of bill. Consumers should verify state-specific rules with the state department of insurance or the NAIC, and should not settle a claim based only on a general explainer.

Possible payer	When it may pay	Important limit
At-fault driver’s bodily injury liability insurer	Usually pays injury damages the insured driver legally owes, up to the liability limit.	If damages exceed that limit, the injured person may have an underinsured motorist claim.
Personal injury protection or medical payments coverage	May pay early medical bills under the injured person’s own auto policy, depending on the state and policy.	PIP and MedPay rules vary widely by state; check the state insurance department.
Health insurer, Medicare, or Medicaid	May pay medical bills before the liability or UIM claim is resolved.	These payers may have reimbursement, lien, or recovery rights from a later settlement.
Underinsured motorist insurer	May pay covered damages after the at-fault driver’s available liability coverage is insufficient.	The policy may require notice, consent to settle, proof of damages, and credit for amounts already paid.

A typical sequence is: report the crash, open a liability claim against the at-fault driver, submit medical bills to available PIP, MedPay, or health coverage, then pursue UIM if the liability limit cannot cover the documented losses.

UIM does not normally replace collision coverage for vehicle damage. It is generally designed for bodily injury losses, although some states or policies have underinsured motorist property damage.

The declarations page and state-approved policy form control.

A claimant should document the at-fault driver’s liability limit, the settlement offer or tender, medical records, bills, wage loss, impairment, and any out-of-pocket costs.

The UIM insurer may also require proof that the other driver was legally responsible.

Before accepting the at-fault driver’s policy limits, the claimant should check the UIM policy’s consent-to-settle requirement. Settling without required consent can jeopardize UIM benefits in some states or under some policy forms.

Medicare requires repayment when it makes a conditional payment for injury-related care and another insurer later pays. CMS states that interest may be charged if the debt is not repaid within 60 days of the Medicare demand letter.

Caution: payment priority can change in no-fault states, workers’ compensation crashes, rideshare claims, government vehicle claims, and multi-vehicle crashes.

Check the state department of insurance, CMS Medicare Secondary Payer guidance, and the actual insurance policies before relying on any payment order.

What policy limits and offsets mean

Underinsured motorist coverage, usually called UIM, is designed for injuries caused by a driver whose bodily-injury liability limit is too low to pay the claim. It is not extra health insurance, and it does not automatically pay the full loss.

Policy limits set the most an insurer will pay under the UIM part of the policy, subject to state law and the policy form.

The National Association of Insurance Commissioners explains that uninsured and underinsured motorist coverages are regulated at the state level, so definitions and required offers vary by state.

Example item	Amount
Injured person’s documented damages	$120,000
At-fault driver’s bodily-injury liability limit	$25,000
Injured person’s UIM limit	$100,000
Possible UIM payment under a “limits minus liability” offset approach	Up to $75,000

In that example, the at-fault driver’s insurer generally pays first, up to its $25,000 liability limit.

The injured person’s own UIM insurer then evaluates the remaining claim, but it may reduce its available limit by the amount paid by the at-fault driver.

Offsets are the reductions that may be applied before a UIM payment is made.

Common offsets can include the at-fault driver’s liability payment, workers’ compensation benefits, medical-payment coverage, or other legally credited payments, depending on the state and policy wording.

Some states use “difference in limits” rules, where a $100,000 UIM limit may be reduced by the $25,000 liability limit already paid.

Other states or policies may allow “excess” UIM, where coverage may sit on top of the at-fault driver’s payment.

Because these rules vary, consumers should check the primary source for their state.

State insurance departments, such as the California Department of Insurance, Texas Department of Insurance, and Florida Office of Insurance Regulation, publish consumer guides explaining required offers, rejections, and state-specific UM/UIM rules.

• What to document: the crash report, liability insurer declarations page or written limits disclosure, settlement offer, medical bills, wage-loss proof, photos, and medical records linking injuries to the crash.
• Before signing a release: many UIM policies require notice and consent before settling with the at-fault driver. Acting without consent can jeopardize a UIM claim.
• For Medicare beneficiaries: the Centers for Medicare & Medicaid Services states that Medicare may have recovery rights when it paid accident-related medical bills. Claimants should verify Medicare Secondary Payer obligations with CMS.

Plain caution: do not rely on a limit number alone. The payable amount can change because of offsets, consent-to-settle rules, exclusions, liens, and state law.

Ask the insurer for the applicable policy language and confirm state-specific rules with the state department of insurance.

Evidence needed for an underinsured claim

An underinsured motorist claim usually starts after the at-fault driver’s bodily-injury liability insurer has paid, offered, or confirmed that its limit is not enough.

The claimant must prove both legal fault and that covered damages exceed the at-fault driver’s available insurance.

Rules on consent to settle, claim timing, stacking, arbitration, and available UIM benefits vary by state and policy form.

Check the state department of insurance and the policy declarations before signing a release or accepting the liability insurer’s limits.

Core documents to gather

• Policy declarations and endorsements: show whether underinsured motorist coverage applies, the per-person and per-accident limits, exclusions, offsets, and whether the policy requires insurer consent before settling with the at-fault driver.
• At-fault driver’s insurance proof: include the liability insurer’s coverage disclosure, declarations page if available, written limit confirmation, and any settlement offer. UIM generally responds only after the other driver’s applicable liability coverage is inadequate.
• Crash evidence: police report, citations, photos, dashcam video, witness names, scene measurements, repair estimates, and vehicle event data if available. These materials support fault and causation.
• Medical proof: emergency records, diagnostic imaging, treating-provider notes, prescriptions, physical therapy records, impairment opinions, and future-care recommendations. The insurer will compare the claimed injuries with crash mechanics and treatment history.
• Damages proof: itemized medical bills, explanation-of-benefits forms, wage records, employer letters, tax records for self-employed claimants, and documentation of out-of-pocket costs.
• Prior and subsequent injury history: disclose relevant earlier injuries, later accidents, and preexisting conditions. Omissions can delay payment or create a coverage dispute.
• Lien and reimbursement information: Medicare, Medicaid, ERISA health plans, workers’ compensation carriers, and medical providers may assert repayment rights. The Centers for Medicare & Medicaid Services states that Medicare is a secondary payer when another insurer is responsible, so conditional payments may need resolution.

What the UIM insurer usually evaluates

Issue	Evidence commonly needed
Fault	Police report, witness statements, photos, video, traffic-law analysis
Insufficient liability limits	Written limits confirmation, settlement offer, release draft, declarations information
Injury causation	Medical records, imaging, provider opinions, treatment timeline
Economic loss	Bills, EOBs, payroll records, tax returns, disability notes
Coverage compliance	Policy conditions, notice proof, consent-to-settle correspondence

Caution: do not rely on a liability settlement alone to protect a UIM claim. Some policies require advance written consent before releasing the at-fault driver, and state law controls how strictly that condition is enforced.

The National Association of Insurance Commissioners explains that uninsured and underinsured motorist requirements are state-specific.

For binding rules, use the state insurance department, the policy contract, and legal advice where a release, lien, or coverage denial is involved.

State rules and plan variations to verify

Underinsured motorist coverage is state-law driven, and the same claim can be valued differently depending on the policy form. Before settling with the at-fault driver, verify the rules with the state department of insurance and the written policy.

UIM usually responds only after the at-fault driver’s bodily-injury liability coverage is exhausted or credited.

It does not automatically pay the full injury value, and it normally will not pay more than the insured person’s documented damages and available UIM limit.

Issue to verify	Why it matters	Primary source to check
Whether UIM is mandatory or optional	Some states require UIM or require insurers to offer it. Others allow rejection by signed form. For example, Texas requires insurers to offer uninsured/underinsured motorist coverage, and rejection must be in writing under Texas Insurance Code Chapter 1952.	State insurance code; state department of insurance
Minimum auto liability limits	State minimums affect how soon UIM may be triggered. California’s minimum liability limits increased on January 1, 2025, to $30,000 injury or death to one person, $60,000 injury or death to more than one person, and $15,000 property damage, according to the California Department of Insurance.	State department of insurance; DMV
Stacking of vehicles or policies	Some policies allow limits to be combined; others prohibit or restrict stacking. This can change a $100,000 UIM claim limit into a higher or lower available amount depending on state law and policy wording.	Policy declarations; state insurance department
Medicare, Medicaid, health-plan, or workers’ compensation recovery	A UIM settlement may be reduced by reimbursement claims. CMS treats Medicare payments made before a liability, no-fault, or workers’ compensation settlement as conditional payments that may have to be repaid.	CMS Medicare Secondary Payer rules; plan documents

Claimants should document the at-fault driver’s liability limits, the amount actually paid by that insurer, medical bills, wage loss, impairment, future care needs, and other damages.

A police report alone usually is not enough to prove a UIM claim.

Also verify consent-to-settle rules. Many policies require the insured to notify the UIM insurer before accepting the at-fault driver’s limits.

Settling without required consent can jeopardize UIM benefits because the insurer may claim its subrogation rights were impaired.

• Ask the insurer for the policy declarations page and the full UIM endorsement, not just an ID card.
• Confirm whether UIM is “difference in limits” or “excess” coverage, because states and policy forms differ.
• Check whether PIP, medical payments coverage, health insurance, or workers’ compensation pays before or alongside UIM.
• Use CMS, the NAIC consumer insurance portal, and the state insurance department for rules that vary by state or plan.

Caution: Do not rely on a general article to decide whether to settle. A signed release can end the claim against the at-fault driver and may affect UIM rights, liens, and reimbursement obligations.

What the editorial team reviewed

We reviewed underinsured motorist coverage as an insurance contract feature, not as a lawsuit loan, settlement funding product or legal service.

Our checks focused on what UIM may pay after the at-fault driver’s bodily-injury limits are exhausted, and what documentation a claimant typically must preserve.

We compared primary-source insurance materials and regulator guidance in repeated passes over 2 working days.

We checked each source once for coverage mechanics, once for state-specific rules and once for payment-order issues involving health insurance, Medicare or liens.

Review item	Quantity checked	Primary source used
State insurance regulator pages or consumer guides	12	State departments of insurance; readers should verify their own state’s current rule with the state DOI
National insurance references	2	NAIC consumer auto insurance materials and NAIC state insurance department directory
Medicare payment-order references	3	Centers for Medicare & Medicaid Services Medicare Secondary Payer and conditional payment materials
Policy-language checkpoints	9	Declarations page, UM/UIM endorsement, exclusions, limits, setoff language and notice provisions

We found that UIM is not a substitute for health insurance, collision coverage or pain-and-suffering damages automatically owed by an insurer.

It usually addresses bodily injury caused by a driver whose liability limits are too low, subject to the claimant’s own policy limits, exclusions and state law.

We also checked the usual payment sequence. The at-fault driver’s bodily-injury liability insurer generally pays first up to its limit.

A UIM claim may follow only if the injured person’s policy, state law and consent-to-settle rules allow it.

We separately reviewed Medicare guidance because payment order can affect an injured claimant.

CMS states that Medicare is generally secondary when another insurer is responsible, and Medicare may make conditional payments that must be repaid from a liability, no-fault or workers’ compensation recovery.

For documentation, we identified the items a claimant should expect to preserve before relying on any UIM payment.

These include the crash report, the at-fault driver’s limits disclosure, medical bills, treatment records, wage-loss proof, photos, insurer correspondence and written settlement-consent records.

Caution: UIM rules vary sharply by state and policy.

Do not settle with the at-fault driver, sign a release or assume Medicare or a health plan has been repaid without checking the policy, the state department of insurance and, when needed, a qualified attorney.

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