Key Takeaways
Uninsured & Underinsured Motorist Coverage
Uninsured motorist (UM) coverage pays for your injuries and, in some cases, vehicle damage when the driver who caused your accident has no auto insurance. Underinsured motorist (UIM) coverage activates when the at-fault driver has insurance, but their policy limits are too low to fully cover your losses. Together, these two protections prevent you from bearing the financial burden of someone else's inadequate coverage.
UM and UIM coverage are often written as a split limit (e.g., $25,000 per person / $50,000 per accident) or a single combined limit, and some states allow — or require — stacking across multiple vehicles on the same policy.
Why UM and UIM Coverage Exist
The U.S. auto insurance system is built on a fault-based principle: the driver who causes a crash is financially responsible for the resulting injuries and damage. In practice, that system has a significant flaw — it only works when the at-fault driver actually has adequate insurance.
An estimated one in eight drivers on American roads carries no auto liability insurance at all, according to the Insurance Research Council. Millions more carry only state-minimum limits, which in many states remain as low as $10,000 or $25,000 per person — amounts that can be exhausted quickly by a single emergency room visit.
UM and UIM coverage exist precisely to close this gap. Rather than pursuing an uninsured driver in civil court (a process that is slow, expensive, and often fruitless), you file a claim with your own insurer instead. For a broader look at how these coverages fit alongside liability, collision, and comprehensive protections, see Auto Insurance Coverage Types, Decoded.
1 in 8
U.S. drivers estimated to be uninsured
According to the Insurance Research Council, roughly 12–13% of motorists nationwide drive without any auto insurance coverage.
$10,000
Lowest state minimum liability per person
Several U.S. states set bodily injury liability minimums as low as $10,000 per person — an amount easily exceeded by a single emergency room visit.
~50%
States requiring UM coverage by law
Roughly half of U.S. states mandate uninsured motorist coverage in some form; requirements for underinsured motorist coverage vary further.
How UM and UIM Coverage Each Work
Uninsured Motorist (UM) Coverage responds when the driver who caused your accident has absolutely no auto insurance. It generally covers:
- Medical expenses for you and your passengers
- Lost wages resulting from your injuries
- Pain and suffering damages
- In some states, property damage to your vehicle (called Uninsured Motorist Property Damage, or UMPD)
Underinsured Motorist (UIM) Coverage activates when the at-fault driver does have insurance — just not enough of it. UIM pays the gap between their liability limit and your actual covered losses, up to your own UIM policy limit. It does not pay until the at-fault driver's coverage is exhausted first.
Because UM and UIM protect against entirely different scenarios, many policies sell them as a paired coverage, while others allow you to purchase them separately. Either way, both coverage amounts are subject to the per-person and per-accident limits shown on your declarations page.
Check Your Declarations Page for Actual Limits
Your UM and UIM limits appear on the declarations page of your policy — the summary sheet that lists each coverage type and its dollar amount. If your UM/UIM limits are equal to or lower than your liability limits, consider whether they would realistically cover a serious injury claim. A licensed insurance agent can help you evaluate whether your current limits match your exposure.
State Requirements and What Your Policy Might Not Cover
State law governs whether UM/UIM coverage is mandatory, optional, or somewhere in between. Roughly half of U.S. states require drivers to carry at least some form of UM coverage. Most of those also require UIM, though the specific minimums differ widely.
Even where UM/UIM is optional, insurers in most states are required to offer it — meaning you actively have to decline it in writing if you choose not to purchase it. That distinction matters: many drivers who waived the coverage years ago may not recall doing so.
Common coverage gaps worth understanding:
- Property damage: Standard UM bodily injury coverage does not pay for vehicle repairs. UMPD is typically a separate election, and some states don't offer it at all — making collision coverage the more practical vehicle-repair backstop.
- Deductibles: Some states allow insurers to apply a deductible to UMPD claims, reducing your net payout.
- Named driver exclusions: Certain household members excluded from your policy may not be covered under UM/UIM either.
Understanding state minimums versus fuller coverage elections is important context here — State Minimum Coverage vs. Full Coverage explains the tradeoffs in detail.
UM/UIM Is General Education, Not Personal Advice
Coverage terms, mandatory minimums, exclusions, and claim procedures vary by state and by individual insurer. The information here is intended to build general understanding, not to serve as personalized insurance or legal advice. Always read your actual policy documents and consult a licensed insurance agent or adviser for guidance specific to your situation.
UM/UIM Compared to Other Injury Coverages
UM/UIM bodily injury is not the only coverage designed to pay for accident-related medical costs. Personal Injury Protection (PIP) and Medical Payments coverage (MedPay) also cover injury expenses — but they work differently.
PIP and MedPay pay regardless of fault, and they pay your bills first, often quickly. UM/UIM, by contrast, is fault-based: it requires that another driver be legally responsible for your losses, and that driver must be uninsured or underinsured. For situations involving a clearly at-fault uninsured driver, UM can ultimately provide higher limits and broader categories of compensation (including lost income and pain and suffering) than MedPay typically offers.
The two approaches often work together in a claim sequence rather than in opposition. Personal Injury Protection and Medical Payments Coverage: The Key Differences walks through how these coverages interact and where each fits best.
It's also worth knowing that many drivers carry assumptions about what their policy covers that turn out to be incorrect. Things Drivers Get Wrong About What Their Auto Insurance Covers — including those about UM/UIM — are explored in detail in our separate guide on coverage misunderstandings.