Uninsured motorist coverage pays for your injuries, and in some states your vehicle damage, when an at-fault driver has no auto liability insurance or cannot be identified after a hit and run. Underinsured motorist coverage picks up where an at-fault driver's too-small liability limits stop. Both coverages live on your own policy, so you claim against your own insurer instead of chasing a driver who has nothing to collect. The premium is small relative to what it protects, and in most states you must sign a written waiver to remove it.
The exposure is not theoretical. According to the Insurance Research Council's study Uninsured and Underinsured Motorists: 2017 to 2023, released in 2025, 15.4 percent of U.S. drivers were uninsured in 2023, more than one in seven, and one in three drivers was either uninsured or underinsured. Here is how the coverage works, personal and commercial.
Uninsured Motorist Coverage
Uninsured motorist coverage is first-party auto insurance that pays for bodily injury, and sometimes vehicle damage, caused by an at-fault driver who carries no liability insurance or flees the scene. It substitutes your own insurer for the missing one, up to the UM limit you purchased.
What Is Uninsured Motorist Coverage?
Uninsured motorist coverage is a first-party coverage on your own auto policy that steps into the shoes of the liability insurance the at-fault driver should have carried. When a driver with no insurance injures you, your UM coverage pays what their liability policy would have paid: medical expenses, lost income, and general damages, up to your UM limit. A driver carrying 100/300 UM limits can collect up to $100,000 per injured person and $300,000 per accident from their own insurer for a single crash.
The coverage also applies when the at-fault driver's insurer denies coverage or becomes insolvent, and in most states when a hit-and-run driver cannot be found. You are the claimant.
That last point changes how the claim feels. Instead of a friendly adjuster from your carrier and an adversary from theirs, your own insurer evaluates your damages the way a liability insurer would, and disputes typically go to arbitration rather than a lawsuit against the phantom driver. UM coverage generally follows people rather than vehicles, so it covers you and resident family members as pedestrians, cyclists, and passengers in other cars, not just in your own listed vehicle.
What Is the Difference Between UM Bodily Injury and UM Property Damage?
Uninsured motorist coverage splits into two parts that are bought, priced, and triggered separately. Uninsured motorist bodily injury (UMBI) pays for injuries to you and your passengers, and it is the part state laws care about. Uninsured motorist property damage (UMPD) pays for damage to your vehicle, and it usually comes with a cap, a deductible, or an identification requirement that UMBI does not have. Confusing the two is the most common UM mistake buyers make.
If you carry collision coverage, UMPD adds little, since collision already pays for your car regardless of who hit it. Where UMPD earns its premium is on vehicles without collision, or in states where it reimburses your collision deductible after an uninsured driver hits you.
The table below compares the pieces:
| Coverage | What it pays | Watch for |
|---|---|---|
| UM bodily injury | Medical bills, lost wages, pain and suffering for you and your passengers | The core coverage. Limits written per person / per accident, like 100/300 |
| UM property damage | Repair or total loss of your vehicle | Low caps in some states ($3,500 in California), and hit-and-run claims often excluded |
| Underinsured motorist | The shortfall when the at-fault driver's limits are less than your damages | Offset vs excess math varies by state |
How Does Underinsured Motorist Coverage Work?
Underinsured motorist coverage responds when the at-fault driver has liability insurance, just not enough. A driver carrying a state-minimum policy who causes $200,000 in injuries is functionally uninsured for most of your claim. In California, where the minimum limit is now $30,000 per person, that driver's insurer pays $30,000 and stops.
UIM fills the gap, but how much it pays depends on whether your state follows the offset approach or the excess approach. In offset states, sometimes called gap or reduced-by states, your UIM limit is reduced by every dollar the at-fault driver's insurer pays. In excess states, your UIM limit sits on top of their payment.
The difference is enormous at equal limits. Run the numbers once and you never forget them.
Offset mechanics carry a practical trap: if your UIM limit merely matches the state minimum, the credit for the at-fault driver's payment can wipe out your coverage entirely. Brokers in offset states should quote UIM limits meaningfully above the local minimum, because that spread is the only part of the limit that can ever pay.
What Is Stacking in Uninsured Motorist Coverage?
Stacking means combining UM/UIM limits across multiple vehicles or multiple policies to create a larger pool for one accident. With stacked coverage, a household insuring three cars at $50,000 UM each may access $150,000 for a single injury. Roughly 30 states permit some form of stacking, while others, including California, Arizona, Illinois, and Michigan, prohibit it and apply one limit per accident no matter how many vehicles are insured.
Florida and Pennsylvania put the stacked vs unstacked insurance choice on the application directly: stacked coverage costs more, and you can sign a waiver to buy unstacked coverage at a discount.
Where stacking is available, the election appears on the application as a checkbox most buyers never notice. Multi-car households in stacking states should price both versions before waiving anything, because stacked UM is often the cheapest way to multiply protection without raising the per-vehicle limit. In anti-stacking states the decision is made for you, so the only lever left is buying a higher limit outright.
Does Insurance Cover a Hit and Run?
Yes, through uninsured motorist coverage: most states treat a hit-and-run driver as an uninsured motorist for bodily injury, though the claim comes with proof requirements designed to screen out staged claims. California is typical: Insurance Code section 11580.2 requires actual physical contact between the unidentified vehicle and you or your car, a police report within 24 hours, and a sworn claim to your insurer within 30 days. A car that runs you off the road without touching you fails the contact test, though some states accept corroborating witness testimony instead.
Property damage is stingier. California's UMPD statute requires the at-fault owner or driver to be identified, by name or license plate, so a pure hit and run where nobody got the plate is a collision claim or nothing. The operational lesson for any driver: photograph the scene, get the plate if humanly possible, and call the police from the curb, because the 24-hour report clock is the first thing the UM adjuster checks.
How Does Uninsured Motorist Coverage Work in California?
California builds uninsured motorist coverage into every auto liability policy by statute. Insurance Code section 11580.2 requires insurers to include UM bodily injury coverage unless the named insured signs a written waiver deleting it or selecting reduced limits, and that agreement stays in force until revoked.
Since January 1, 2025, Senate Bill 1107 raised the state's minimum liability limits to $30,000 per person and $60,000 per accident, and the required UM offer moves with them: UMBI limits must equal your liability limits, though the insurer need not offer more than 30/60. California is an offset state for UIM and prohibits stacking.
UMPD in California is its own animal under Insurance Code section 11580.26. It pays the lesser of your vehicle's actual cash value or $3,500, requires the uninsured driver or vehicle to be identified, and demands a report to your insurer within 10 business days. If you carry collision, collision pays first and UMPD covers only your deductible.
Waiving UMBI in California saves little and forfeits the only realistic recovery against the state's large uninsured driver population. Keep it, and match it to your liability limits.
Do I Need Uninsured Motorist Coverage if I Have Full Coverage?
Yes, because "full coverage" does not include it. Full coverage is shorthand for liability plus comprehensive and collision, and none of those three pays for your injuries when someone else hits you.
Your liability coverage pays people you injure. Collision fixes your car but pays nothing for your medical bills, lost wages, or pain and suffering. Health insurance covers treatment but not lost income or general damages, and it comes with deductibles, network limits, and often a lien against any recovery. UM bodily injury is the only coverage on the list that replaces the at-fault driver's missing liability policy.
The honest counterargument is narrow: a driver with unusually rich health, disability, and life insurance duplicates some of what UMBI does. Even then, UM remains the only source for general damages and the only coverage protecting your passengers' full claim. For the price, typically a small fraction of the liability premium, carrying it is the correct call for almost everyone.
How Much Uninsured Motorist Coverage Should You Buy?
Match your UM/UIM limits to your liability limits. That is the standing rule, and it works for two reasons. First, most insurers will not sell UM limits higher than your liability limits, so your liability selection sets the ceiling. A driver carrying 100/300 liability should therefore be quoted 100/300 UM/UIM, which typically adds a small fraction of the liability premium.
Second, the logic of the coverage is symmetry: whatever injury severity made you buy $250,000 of protection for strangers applies equally to your own family in the passenger seats. Buying 250/500 liability with 30/60 UM says a stranger's spine is worth more than yours.
Check your umbrella too. Personal umbrella policies raise your liability protection but usually exclude UM/UIM unless you buy an excess UM endorsement, which only some carriers offer. If your household's real injury exposure runs past your auto policy's UM ceiling, that endorsement is the only way to push UM limits into umbrella territory, and it is worth asking for by name.
How Does UM/UIM Work on a Commercial Auto Policy?
On a Business Auto Policy, uninsured and underinsured motorist coverage appears as separate line items in the declarations, activated by state-specific endorsements rather than the base CA 00 01 coverage form. ISO publishes a distinct UM endorsement for each state in the CA 21 series, which is why a fleet garaged in three states carries three different UM endorsements with three different rules.
Each coverage line also needs a covered auto symbol beside it: symbols 2, 3, 4, and 7 support UM, symbol 1 supports liability only, and symbol 6 exists specifically for autos garaged in states where UM is compulsory and cannot be rejected, such as North Dakota and South Dakota.
Fleet accounts generate UM paperwork brokers have to manage deliberately. Every state where vehicles are garaged has its own offer, rejection, and limit-selection form, and a missing or defective rejection form can read UM coverage into the policy at full liability limits by operation of law.
Executives without personal autos are a second exposure: the Drive Other Car endorsement (CA 99 10) can extend UM and UIM to named individuals for personal use of non-owned vehicles, and its UM and medical payments coverage reaches the listed individual's resident spouse and family members while occupying, or struck as pedestrians by, non-owned autos. Sole proprietors get similar personal-lines treatment through the Individual Named Insured endorsement (CA 99 17) at no additional premium.
Frequently asked questions
Is uninsured motorist coverage required by law?
It depends on the state. Some states make UM bodily injury mandatory and non-waivable, which is what business auto symbol 6 exists for. Many others, including California, require insurers to include it unless you sign a written rejection. No state forbids you from carrying it, and the written waiver is the only way it legitimately disappears from a policy.
Does uninsured motorist coverage pay for damage to my car?
Only the property damage part, UMPD, and only where it is offered. UM bodily injury never pays for vehicles. UMPD often carries restrictions, such as California's $3,500 cap and its requirement that the uninsured driver or vehicle be identified. If you carry collision coverage, your car is already protected and UMPD mainly serves to reimburse the deductible.
What happens if I rejected UM coverage and an uninsured driver hits me?
Your own policy pays nothing for your injuries, and your recovery is limited to suing a driver who, by definition, had no insurance and likely has few collectible assets. Health insurance covers treatment but not lost wages or pain and suffering. You can revoke a UM waiver at any renewal, and often mid-term, by asking your insurer in writing.
Is underinsured motorist coverage worth it if I already have health insurance?
Yes, for most people. Health insurance pays medical bills only, subject to deductibles and networks, and your health plan may assert a lien to be repaid out of any injury recovery. UIM covers lost income and general damages that no health plan touches, and it protects your passengers. The two coverages overlap far less than they appear to.
This guide is for educational purposes and summarizes standard ISO policy language. Your policy's specific terms, conditions, and endorsements control. Talk to a licensed broker about your actual exposures.
