Uninsured and underinsured motorist coverage pays for your injuries and vehicle damage when the other driver either has no insurance or doesn't have enough to cover what you're owed

If another driver hits you and has no insurance, your own car insurance won't automatically cover your medical bills or repairs—unless you've bought uninsured motorist (UM) coverage or underinsured motorist (UIM) coverage. These are separate add-ons to your policy that protect you when the at-fault driver can't or won't pay.

The difference is straightforward: uninsured motorist coverage handles crashes with drivers who have zero insurance. Underinsured motorist coverage kicks in when the other driver's insurance exists but isn't enough to cover your losses. Many states require you to carry at least one of these; others make it optional. Either way, it's one of the most practical protections you can buy, because uninsured drivers are common, and even insured drivers often carry low limits.

Key Takeaways

  • Uninsured motorist coverage pays your medical bills and vehicle damage when hit by a driver with no insurance; underinsured motorist coverage covers the gap when their insurance isn't enough.
  • Your state either requires one or both of these coverages or lets you decline them in writing, but declining leaves you personally responsible for losses you can't recover from the other driver.
  • These coverages use the same limits you choose for liability insurance—typically $25,000 to $100,000 per person—and cost $15 to $30 per month depending on your state and driving record.
  • You can use this coverage even if you're partially at fault, though the payout may be reduced by your share of blame in states that follow comparative negligence rules.
  • Hit-and-run crashes are usually covered under uninsured motorist protection, but you'll need to file a police report and show you made a reasonable effort to identify the other driver.

How uninsured motorist coverage works after a crash

When an uninsured driver hits you, you report the crash to your own insurance company, not to the other driver's (because they don't have one). You'll file a claim just as you would for any other collision, providing the police report, photos, medical records, and repair estimates. Your insurer then pays your medical expenses, lost wages, and pain and suffering up to the limit you chose when you bought the policy.

The catch is that your insurer will investigate whether the other driver actually had no insurance. They'll run a database check and may contact the other driver directly. If the other driver turns out to have had insurance but simply didn't disclose it, your claim shifts to underinsured motorist coverage instead. If they truly had nothing, uninsured motorist coverage pays.

You'll also need to prove the other driver was at fault. If you were partially at fault—say, you were speeding but the other driver ran a red light—the payout may be reduced by your percentage of fault. The exact reduction depends on your state's negligence rules, which vary.

How underinsured motorist coverage protects you when their insurance isn't enough

Underinsured motorist coverage is designed for situations where the at-fault driver has insurance but their limits are too low to cover your actual losses. For example, if another driver causes $80,000 in medical bills and vehicle damage but only carries $25,000 in liability coverage, their insurance pays that $25,000 and stops. Your underinsured motorist coverage then pays the difference—up to your own policy limit.

You can only recover from underinsured motorist coverage after the at-fault driver's insurance has paid out completely. Your insurer will coordinate the payments so you don't collect twice for the same loss. If your underinsured motorist limit is $50,000 and the other driver's liability limit is $25,000, you can receive up to $50,000 total—not $75,000.

This coverage is especially valuable because many drivers carry minimum liability limits, which in most states are $25,000 or less. A serious injury or totaled vehicle can easily exceed that, leaving you to absorb the rest of the cost.

State requirements and your right to decline

About half of U.S. states require uninsured motorist coverage as part of any auto policy. Some require both uninsured and underinsured motorist coverage; others require only one. A few states don't require either but strongly encourage it. Your insurance company will tell you what's mandatory in your state when you buy or renew a policy.

In states where these coverages are required, you can usually decline them only by signing a written waiver. This waiver stays in your file, and you'll need to sign it again if you switch insurers or renew your policy. Declining means you're choosing to accept the financial risk if you're hit by an uninsured or underinsured driver.

In states where these coverages are optional, they're still worth buying. The cost is low—typically $15 to $30 per month—and the protection is substantial. Uninsured drivers make up roughly 10 to 15 percent of drivers on the road in most states, so the risk is real.

Coverage limits and how they affect your cost

Uninsured and underinsured motorist coverage uses the same limit structure as your liability insurance. You choose a per-person limit and a per-accident limit. Common options are $25,000 per person / $50,000 per accident, $50,000 per person / $100,000 per accident, or $100,000 per person / $300,000 per accident.

The per-person limit is what one injured person can recover from your policy. The per-accident limit is the total your policy will pay for all injuries in a single crash. If three people are injured in one accident and each has $30,000 in medical bills, a $25,000 per person / $50,000 per accident policy would pay $25,000 to each of the first two people and nothing to the third, because the per-accident limit is exhausted.

Higher limits cost more but provide better protection. The difference between $25,000 and $50,000 limits is usually $5 to $10 per month. If you have significant assets or a high income, higher limits make sense because they protect you if your losses exceed the other driver's insurance. If you're in a state that requires these coverages, the minimum required limit is often $25,000 per person, but you can choose higher.

Hit-and-run crashes and uninsured motorist coverage

Hit-and-run crashes—where the other driver leaves the scene—are usually covered under uninsured motorist protection because you can't recover from a driver you can't identify. However, your insurer will require proof that you made a reasonable effort to find them. This means filing a police report immediately and providing the report number with your claim.

Some states also require that you have a police report documenting that the other vehicle made contact with yours. A fender-bender in a parking lot where you didn't see the other car may not may have access to unless a witness or security camera confirms another vehicle was involved. Your insurer will review the police report to determine whether the hit-and-run meets the definition in your policy.

If you hit a parked car and leave, that's a different situation—you're the uninsured driver from the other person's perspective, and they can use their uninsured motorist coverage against you.

Stacking and how it works in your state

Stacking is the ability to combine uninsured motorist limits across multiple vehicles or policies to increase your total recovery. For example, if you own two cars, each with $50,000 uninsured motorist coverage, some states let you stack those limits to recover up to $100,000 if you're hit by an uninsured driver while driving either vehicle.

Not all states allow stacking, and the rules vary widely. Some states allow it only if you own multiple vehicles; others allow it only if you have multiple policies with the same insurer. A few states prohibit it entirely. Your insurance company can tell you whether stacking is available in your state and whether your policy allows it. If it does, you can usually choose to stack or not stack when you buy the policy.

Stacking can significantly increase your protection at minimal cost, so it's worth asking about. If your state allows it and your insurer offers it, it's usually a good choice—especially if you drive frequently or carry passengers.

What uninsured and underinsured motorist coverage does not cover

These coverages pay for your medical bills, lost wages, pain and suffering, and vehicle damage caused by the uninsured or underinsured driver. They do not cover damage to someone else's vehicle or injuries to someone else—that's what your liability coverage is for. They also do not cover your own vehicle damage if you caused the crash, even if the other driver was uninsured.

Uninsured and underinsured motorist coverage also does not apply if you're hit by a vehicle owned by your household or by your employer's vehicle if you were using it for work. In those cases, the vehicle owner's insurance is responsible. It also does not cover intentional damage or damage from your own vehicle (for example, if your brakes fail and you hit a parked car).

If you're injured as a pedestrian or cyclist by an uninsured driver, uninsured motorist coverage may still apply, but the rules vary by state. Some states extend it to pedestrians and cyclists; others limit it to occupants of insured vehicles. Check your policy or ask your insurer.

Frequently Asked Questions

Do I have to carry uninsured motorist coverage?

It depends on your state. About half of U.S. states require it; the others make it optional. Even in states where it's optional, it's inexpensive and protects you against a real risk. If your state requires it, you can decline only by signing a written waiver.

What if I'm partially at fault for the crash?

You can still use uninsured motorist coverage, but the payout may be reduced by your share of fault. In states that follow comparative negligence, if you were 20 percent at fault, your recovery is reduced by 20 percent. In states that follow contributory negligence, being any percentage at fault can bar recovery entirely, though this is rare.

Can I use uninsured motorist coverage if the other driver's insurance company denies my claim?

Not directly. Uninsured motorist coverage applies when the other driver has no insurance or insufficient insurance. If they have insurance but their company denies your claim, you would need to pursue a lawsuit against the other driver or their insurer. Uninsured motorist coverage doesn't cover disputes over fault or coverage.

How much does uninsured and underinsured motorist coverage cost?

Typically $15 to $30 per month, depending on your state, driving record, and the limits you choose. Higher limits cost more, but the difference is usually small. It's one of the least expensive add-ons to a car insurance policy.

What happens if my medical bills exceed my uninsured motorist limit?

You're responsible for the amount over your limit. This is why choosing an appropriate limit matters. If you have significant medical expenses or assets, higher limits provide better protection. You cannot recover the excess from the uninsured driver unless you pursue a lawsuit and win a judgment, which is difficult if they have no assets or insurance.