Uninsured & Underinsured Motorist Claims: How UM/UIM Works

There is a scenario that turns a strong claim into almost nothing: clear liability, serious injuries, well-documented damages — and an at-fault driver carrying a state-minimum policy. In several states the minimum bodily injury limit is $25,000 or less. A single surgery exceeds it. See our guide to state minimum car insurance requirements for how low that floor actually is where you live.

When that happens, the coverage that decides your outcome is your own, purchased before the crash. Understanding it is the difference between a $25,000 recovery and a $300,000 one on identical facts.

Quick answer: UM covers you when the at-fault driver has no insurance or cannot be identified. UIM covers the gap when their limits are too low. Both are claims against your own insurer — which will defend them like any other liability claim. Never settle with the at-fault driver without your insurer’s written consent.

Why This Coverage Matters More Than People Realize

The Insurance Research Council’s Uninsured and Underinsured Motorists: 2017–2023 (published 2025) puts the uninsured rate at 15.4% — more than one in seven drivers — with enormous state variation, from roughly 5.7% in Maine to 28.2% in Mississippi.

The figure that matters more is the combined one: 33.4% of drivers are uninsured or underinsured — one in three, up around ten points since 2017. That is the real exposure, because a driver carrying only a state minimum is functionally uninsured against a serious injury. (Many articles still quote “one in eight,” which was IRC’s 2019-data finding and is now two report cycles stale.)

Consider a hypothetical with $180,000 in medical bills and lost income:

Scenario	Your recovery
At-fault driver has $250,000 limits	Up to $180,000
At-fault driver has $25,000 limits, you have no UIM	$25,000
At-fault driver has $25,000 limits, you have $250,000 UIM (add-on state)	Up to $180,000
At-fault driver has $25,000 limits, you have $250,000 UIM (offset state)	Up to $180,000, but UIM reduced by the $25,000 paid
Hit-and-run, you have $250,000 UM	Up to $180,000
Hit-and-run, no UM coverage	$0

Same injuries, same fault, five very different outcomes — all decided by paperwork signed before the accident.

A sixth scenario is worth naming separately: a multi-defendant crash in a state that has abolished joint and several liability. See our guides to Arizona, Tennessee and Washington car accident settlements for how a solvent co-defendant generally cannot be made to cover an insolvent one’s share in most of these states — which turns UM/UIM coverage from a hit-and-run and total-uninsured backstop into the practical remedy for an underinsured co-defendant problem as well. (Washington’s version has one narrow exception, covered in that guide, for a claimant found completely free of fault.)

When Each Coverage Applies

Uninsured motorist (UM):

• The at-fault driver has no liability insurance
• Hit-and-run where the driver cannot be identified
• The at-fault driver’s insurer becomes insolvent
• In some states, a phantom vehicle that caused the crash without contact (usually requiring corroboration)

Underinsured motorist (UIM):

• The at-fault driver has insurance, but their limits are less than your damages
• Multiple claimants exhaust a single policy, leaving you underpaid — see our guide to multiple claimants sharing one policy for how that pool actually gets divided, and why speed can matter more than injury severity

The Offset vs. Add-On Distinction

This is the most consequential technical detail in UM/UIM law, and it varies by state:

Add-on (excess) states: UIM stacks on top of the liability recovery. $50,000 from the at-fault driver plus a $100,000 UIM limit gives you access to $150,000.

Offset (reduction) states: the liability payment is subtracted from your UIM limit. $50,000 from the at-fault driver against a $100,000 UIM limit leaves $50,000 of UIM available — total $100,000, not $150,000.

The practical implication: in an offset state, buying UIM limits equal to your liability limits provides less protection than most policyholders assume. Confirm which rule your state applies before deciding your own coverage levels.

Stacking: Multiplying Available Coverage

Where permitted, stacking combines limits:

• Intra-policy stacking — combining limits across multiple vehicles on one policy
• Inter-policy stacking — combining limits across separate policies
• Household coverage — some states allow a resident relative’s policy to apply

Whether stacking is available depends on state law and on the enforceability of anti-stacking clauses in your policy. Where it works, a household with three insured vehicles may have three times the apparent limit available — which is why every policy in the household should be reviewed after a serious crash, not just the one on the car you were driving.

Your Insurer Becomes the Opposing Party

This is the part policyholders find hardest to accept. In a UM/UIM claim, your insurer’s financial position is identical to the at-fault driver’s insurer: every dollar it pays you is a dollar of loss. It will therefore:

• Dispute liability and comparative fault
• Dispute the extent and causation of your injuries
• Request an independent medical examination
• Require recorded statements and possibly an examination under oath
• Assert policy defenses — late notice, lack of consent, coverage exclusions

The relationship is genuinely different in one respect: because it is a contract, your insurer owes you duties of good faith that a third-party insurer does not. Unreasonable denial or delay can expose it to bad faith liability, which in many states permits recovery beyond the policy limits. That leverage exists only if you have documented the claim properly and met every policy condition — see our guide to insurance bad faith claims for what actually crosses the line, and why a low offer alone does not.

The Consent-to-Settle Trap

This is the mistake that destroys UM/UIM claims. Nearly every policy requires the insurer’s written consent before you settle with or release the at-fault driver, so the insurer can preserve its subrogation rights against that driver.

Accepting the at-fault driver’s $25,000 policy limits and signing their release without consent puts your UIM coverage at risk. The sequence must be: notify your insurer, request written consent, obtain it, then settle. Every step in writing.

One important qualification, because this is usually overstated. Forfeiture is not automatic in most states: the majority rule requires the insurer to prove it was actually prejudiced by the settlement — typically that releasing the at-fault driver destroyed a subrogation recovery it would otherwise have made — and the burden sits with the carrier. Several states use a structured notice procedure instead of a flat bar. The leading example is Minnesota’s Schmidt v. Clothier, 338 N.W.2d 256 (Minn. 1983), which gives the UIM insurer 30 days after written notice of a tentative settlement either to consent, waiving subrogation, or to substitute its own payment in the settlement amount and preserve it; New Jersey follows a comparable Longworth notice procedure.

None of that makes it safe to settle without consent — you would be betting your claim on a prejudice argument you may lose, in a state whose rule you may have wrong. It does mean that if you have already signed, the claim is not necessarily over, and it is worth getting advice rather than assuming the worst.

Steps to Preserve a UM/UIM Claim

1. Notify your own insurer promptly, even if the other driver appears insured. Late notice is a policy defense.
2. Read your declarations page and identify your UM/UIM limits — and whether you have any at all. Many states allow written rejection of the coverage.
3. Check every household policy for stacking potential.
4. For hit-and-run, file a police report immediately. Most policies and many statutes require prompt reporting as a condition of UM coverage, often within 24 to 72 hours.
5. Request written consent before settling with the at-fault driver. Never sign their release first.
6. Document as thoroughly as you would against a stranger’s insurer — because functionally, that is the posture.
7. Check your policy for arbitration provisions, which may govern how disputes are resolved and on what timeline.
8. Note the deadline. UM/UIM claims are contractual and your policy may impose a shorter suit deadline than your state’s tort statute of limitations — see our state filing deadline reference.

A Note on Buying Coverage

Because UM/UIM is what actually protects you against the most common bad outcome, it is generally regarded as among the most cost-effective coverage on an auto policy — typically inexpensive relative to the exposure it addresses. Reviewing your limits, and whether you rejected the coverage in writing at some point, is worth doing before you need it.

Sources & Further Reading

• Insurance Research Council, Uninsured and Underinsured Motorists: 2017–2023 (2025) — the source of the 15.4% uninsured and 33.4% uninsured-or-underinsured figures, and the state-by-state range
• Schmidt v. Clothier, 338 N.W.2d 256 (Minn. 1983) — the notice-and-substitution procedure that lets an insured settle with the at-fault driver without forfeiting UIM coverage; New Jersey’s equivalent is the Longworth notice (Longworth v. Van Houten, 223 N.J. Super. 174 (App. Div. 1988))
• O.C.G.A. § 33-7-11 (Georgia) — a clear statutory example of the add-on/reduced-by distinction, where insurers must offer add-on coverage and the insured must reject it in writing to receive the reduced-by form
• State uninsured/underinsured motorist statutes — mandatory offer, written rejection and minimum limits. Pennsylvania and Florida are the standard illustrations of stacking waivers: stacking is the default and a specific written rejection is required to remove it, which is why defective waivers are litigated so often.
• State insurance codes on first-party bad faith and unfair claims settlement practices; the NAIC Unfair Claims Settlement Practices Act (Model #900) as the framework most states adapted
• See our guide to state minimum car insurance requirements — seven states raised their minimums in 2025–2026, which directly changes how often UIM is triggered.
• UM/UIM is frequently the only practical recovery where a fleeing driver caused the crash during a police pursuit — see our guide to emergency vehicle and police pursuit accident claims.
• The same coverage is the primary route after a hit-and-run or a phantom-vehicle incident — see our guide to hit-and-run pedestrian and bicycle accident claims.
• Rideshare drivers have a distinct and frequently misunderstood UM/UIM position under the platform’s policy — see our guide to rideshare drivers using the $1M policy’s UM/UIM coverage.