Legal Injury GuideLast reviewed & updated: 2026
Uninsured & Underinsured Motorist
Coverage — How UM/UIM Protects You
A large share of drivers on the road carry no insurance or far too little to cover a serious crash. When one of them injures you, uninsured and underinsured motorist coverage — UM and UIM — may be the only meaningful source of compensation. This coverage sits on your own auto policy, and understanding how it works, how much you carry, and how to file a claim can be the difference between a full recovery and being left with the bills.
First-party
Coverage type
No insurance
UM covers
Too little
UIM covers
Often covered
Hit-and-run
When UM/UIM Coverage Applies
UM/UIM coverage is triggered by the at-fault driver’s lack of adequate insurance, not by who you are. Knowing the common scenarios helps you recognize when your own policy should be doing the work.
At-fault driver has no insurance
UM coverage steps in to pay for your injuries as if it were the at-fault driver’s liability policy.
At-fault driver is underinsured
UIM coverage pays the gap between the at-fault driver’s low limits and your actual damages, up to your UIM limit.
Hit-and-run
When the driver flees and cannot be identified, UM coverage often applies, subject to your policy’s requirements.
You are a passenger or pedestrian
UM/UIM coverage can extend to household members and, in some cases, when you are struck as a pedestrian.
How a UIM Gap Works
Underinsured coverage fills the gap between an at-fault driver’s limits and your actual damages. Suppose your medical bills, lost wages, and pain and suffering total $120,000, but the at-fault driver carries only $30,000 in liability coverage. If you carry $100,000 in UIM coverage, it can pay the difference up to that limit.
- Your total damages: $120,000
- At-fault driver pays: $30,000
- UIM covers the gap (up to your limit): $90,000
- Total recovered: up to $120,000
What Strengthens or Weakens Your Position
The protection you have depends on the coverage you bought and how you handle the claim.
▲Strengthens Protection
+Higher UM/UIM limits
Carrying limits that match or exceed your liability limits gives you real protection against uninsured drivers.
+Stacking, where allowed
Some states let you stack coverage across multiple vehicles or policies, multiplying available protection.
+Prompt notice and documentation
Reporting quickly and preserving evidence — especially in hit-and-run claims — strengthens the claim.
▼Weakens Protection
–Rejecting or minimizing UM/UIM
Waiving or buying minimal UM/UIM leaves you exposed when an uninsured driver causes serious harm.
–Late reporting of a hit-and-run
Delays can let your own insurer question whether an unidentified vehicle was really involved.
–Treating your insurer as an ally
A UM/UIM claim is against your own carrier, which will still scrutinize and may dispute the claim.
Filing a UM/UIM Claim
Report the accident to your own insurer promptly, review your declarations page to confirm your UM/UIM limits, and document your injuries thoroughly. Because a UM/UIM claim is handled much like any other insurance claim — with the same low first offers — the same negotiation principles apply. If your own carrier unreasonably denies or delays a valid claim, that conduct can raise separate settlement issues worth discussing with an attorney.
Frequently Asked Questions
What is the difference between uninsured and underinsured motorist coverage?
Uninsured motorist (UM) coverage applies when the at-fault driver has no liability insurance at all, including many hit-and-run situations where the driver cannot be identified. Underinsured motorist (UIM) coverage applies when the at-fault driver has insurance, but their limits are too low to cover your damages. UIM pays the difference between what the at-fault driver’s policy covers and your total losses, up to your UIM limit. Both are first-party coverages you carry on your own auto policy.
Why would my own insurance company fight a UM/UIM claim?
Even though you pay premiums for UM/UIM coverage, a claim under it is still a claim your insurer must pay, so the company evaluates it much like any other injury claim. It may dispute the severity of your injuries, argue about fault, or make a low initial offer. This surprises many people who assume their own carrier will be on their side. In practice, a UM/UIM claim is an adversarial process that requires the same documentation and persistence as a claim against another driver.
What is stacking and can I do it?
Stacking is combining UM/UIM limits across multiple vehicles on a policy or across multiple policies to increase the total coverage available for a single accident. For example, stacking $50,000 in coverage across two vehicles could provide $100,000 of protection. Whether stacking is allowed — and whether you must pay extra or affirmatively elect it — depends on your state and policy. Reviewing your declarations page tells you what you actually carry.
Does UM coverage apply to hit-and-run accidents?
In many states, yes. If a driver flees and cannot be identified, UM coverage often treats the phantom vehicle like an uninsured driver, allowing you to recover for your injuries. However, policies frequently impose requirements such as prompt reporting to police and, in some states, independent corroboration of the other vehicle. Reporting the incident immediately and preserving any evidence is important to preserving the claim.
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For informational purposes only. Not legal advice. Consult a licensed attorney.