Uninsured and Underinsured Motorist Coverage: The Protection Most Drivers Overlook
Key Takeaways
- Roughly 1 in 7 U.S. drivers is uninsured, according to Insurance Research Council estimates.
- UM coverage protects you when an at-fault driver has no insurance at all; UIM coverage applies when their limits are insufficient.
- Many states require UM/UIM coverage, but minimums are often low — your own limits matter.
- Hit-and-run accidents may qualify for UM claims, depending on your state's rules.
- UM/UIM coverage is generally considered one of the more cost-effective protections on an auto policy.
Uninsured/Underinsured Motorist Coverage
Uninsured motorist (UM) and underinsured motorist (UIM) coverage are auto insurance add-ons that protect you when an at-fault driver either has no insurance or doesn't carry enough to pay for your injuries and property damage. UM coverage applies when the other driver has zero liability insurance; UIM coverage kicks in when their policy limits are too low to cover your actual losses. Together, they fill a gap that standard liability coverage leaves wide open.
UM/UIM coverage is typically split into two sub-types: bodily injury (UMBI/UIMBI) and property damage (UMPD/UIMPD). Stacking rules — which allow you to multiply coverage limits across multiple vehicles — vary significantly by state law.
Why the At-Fault System Has a Blind Spot
American auto insurance is built on a simple idea: the driver who causes a crash is responsible for the resulting costs. Most states use an at-fault (or "tort") system, meaning the at-fault driver's liability insurance covers injuries and property damage to others. It sounds fair — until you realize that a meaningful share of drivers on U.S. roads either carry no insurance at all or purchase only the bare minimum their state requires.
The Insurance Research Council has estimated that approximately one in eight drivers in the United States is uninsured, with rates in some states considerably higher. Even insured drivers may carry liability limits as low as $25,000 per person — an amount that can be exhausted quickly by a single emergency room visit. If that driver hits you, their policy may not come close to covering your actual losses.
This is the gap that uninsured and underinsured motorist coverage is specifically designed to fill. For a broader foundation on how policies are structured, see Auto Insurance Explained.
~1 in 8
U.S. drivers estimated to be uninsured
According to Insurance Research Council research, roughly one in eight drivers on U.S. roads carries no auto insurance.
$25,000
Common state minimum bodily injury liability limit
Many states set per-person liability minimums as low as $25,000 — an amount that can be exceeded by a single ER visit and overnight hospital stay.
22 states
States that mandate UM coverage
As of recent Insurance Information Institute reporting, roughly 22 states and Washington D.C. require some form of uninsured motorist coverage on all auto policies.
How UM and UIM Coverage Each Work
Uninsured motorist (UM) coverage steps in when the at-fault driver has no liability insurance whatsoever. Your own insurer essentially stands in for the driver who should have been responsible. UM coverage typically applies to bodily injury — medical bills, lost wages, pain and suffering — and in many states also extends to property damage.
Underinsured motorist (UIM) coverage applies when the at-fault driver is insured, but their limits aren't high enough to cover your total losses. For example, if the other driver carries $25,000 in liability but your medical bills reach $80,000, your UIM coverage can help bridge the $55,000 difference — up to your own UIM policy limits.
Both coverages are typically broken into two components:
- Bodily injury (UMBI / UIMBI): Covers medical expenses, rehabilitation, lost income, and pain and suffering for you and your passengers.
- Property damage (UMPD / UIMPD): Covers repairs to your vehicle and other property. Note that in some states, UMPD has limitations or a deductible that UMBI does not.
Understanding how this differs from collision or comprehensive coverage is important — for a clear comparison, see Liability, Collision, and Comprehensive.
State Rules, Stacking, and What to Watch For
UM/UIM requirements vary significantly across states. Some states mandate that insurers include UM/UIM coverage in every policy automatically. Others require insurers to offer the coverage but allow drivers to decline it in writing. A few states have minimal or no requirement. Because state minimums are often low, having only the required amount may not provide adequate protection — particularly for bodily injury claims.
One important nuance is stacking: in states that permit it, you may be able to add together UM/UIM limits across multiple vehicles on your policy. For instance, two vehicles each insured with $100,000 in UIM could provide up to $200,000 in stacked coverage. Not all states allow stacking, and some policies explicitly exclude it, so confirm with your insurer.
Hit-and-run accidents are another area where UM coverage often applies — even when no other driver is identified, most states allow a UM claim as long as certain conditions (such as filing a police report) are met.
Drivers sometimes discover coverage gaps after a claim. Our piece on coverage gaps that leave drivers exposed outlines other situations where standard policies commonly fall short.
This article provides general information about auto insurance concepts and is not personalized insurance, financial, or legal advice. Coverage terms, availability, and requirements vary by state and insurer. Consult a licensed insurance agent or adviser to evaluate your specific situation and review your actual policy documents before making decisions.