Drivers often hear two similar terms and assume they mean the same thing: uninsured vs underinsured motorist. They are related, but they solve different problems. If you mix them up, you can misunderstand what your policy actually does after a crash.
This guide explains the key differences between uninsured motorist (UM) and underinsured motorist (UIM) coverage, what each one may pay for, and the situations where one applies but the other does not. You’ll also see how limits work and what to check on your declarations page.
Quick takeaways
- UM helps when the at-fault driver has no insurance (or can’t be identified in many hit-and-run cases).
- UIM helps when the at-fault driver has insurance, but their limits are too low for a serious loss.
- Both are usually focused on injuries first (medical bills, lost income, and sometimes pain and suffering).
- State rules vary a lot. Your declarations page and policy wording decide what applies.
If you want the bigger “map” of how coverages fit together, start here: What Does Car Insurance Cover?
Definitions: UM vs UIM in plain English
Uninsured motorist (UM)
Uninsured motorist (UM) coverage may help when the driver who caused the crash has no liability insurance. In many states, hit-and-run claims are treated like uninsured claims if the at-fault vehicle cannot be identified and certain reporting rules are met.
UM is the “no insurance” problem.
Underinsured motorist (UIM)
Underinsured motorist (UIM) coverage may help when the at-fault driver does have insurance, but their liability limits are too low to cover a large loss—often a serious injury claim.
UIM is the “not enough insurance” problem.
Comparison table: what’s different?
| Topic | UM (Uninsured) | UIM (Underinsured) |
|---|---|---|
| At-fault driver insurance | No liability insurance (or unknown driver in many hit-and-run cases) | Has insurance, but limits are too low |
| Most common reason it matters | You can’t collect from the at-fault driver’s insurer | You can collect something, but it’s not enough for the loss |
| What it often focuses on | Injury-related losses (UMBI); sometimes property damage (UMPD) | Injury-related losses (UIMBI); property damage UIM is less common |
| Hit-and-run | Often treated as UM if reporting/evidence rules are met | Usually not the hit-and-run tool (because the at-fault driver is unknown) |
| Limits matter? | Yes—your UM limits cap what can be paid | Yes—your UIM limits and state method determine what’s available |
What can UM and UIM pay for?
UM and UIM are usually discussed as injury coverages. That said, some states and policies also include a property-damage version. Always check your declarations page for exact labels.
Bodily injury (most common)
When UM/UIM includes bodily injury coverage, it may help pay for things like:
- Medical bills related to crash injuries
- Lost wages if you can’t work
- Rehabilitation and ongoing treatment (depending on proof and policy rules)
- Pain and suffering (where allowed by state law and policy terms)
These payments are not unlimited—your policy limits matter. If you want a clear explanation of limits, see: Car Insurance Policy Limits: What They Mean and How They Work
Property damage (sometimes)
Some states offer UM property damage (often called UMPD). This may help repair your vehicle when an uninsured driver causes damage. However, it is not available everywhere and may have specific rules or deductibles.
Many drivers rely on collision coverage for repairs after an at-fault crash, even when the other driver is uninsured. Collision is separate from UM/UIM and may apply subject to your deductible.
Real-world examples
Example 1: UM applies
You’re rear-ended at a stoplight. The other driver is clearly at fault, but you learn they have no insurance. Your UM bodily injury coverage may apply for covered injury losses up to your UM limits.
Example 2: UIM applies
You’re hit by a driver who has insurance, but their liability limit is low. Your injuries require extensive treatment and time off work. Their insurer pays up to the driver’s limit, but the loss is bigger. UIM may apply, depending on your state’s rules and how your policy calculates what’s available.
Example 3: Hit-and-run often points to UM
A driver sideswipes you and takes off. If the at-fault vehicle can’t be identified, many states treat this as an uninsured scenario if you follow reporting rules (often a prompt police report) and can show evidence that another vehicle caused the crash.
Some states or policies also require prompt reporting and, in some cases, physical contact or other clear evidence that another vehicle caused the crash.
If you want a dedicated UM overview, see: Uninsured Motorist Coverage: What It Is and When It Helps
How UIM limits work
UIM is where confusion happens most, because states use different methods to calculate what’s available. The short version: UIM is not always “your limit minus their limit”, and it’s not always “extra money on top” either. It depends on your state and policy.
Two common approaches you may hear about are:
- Difference-style approach: the available UIM amount is tied to the gap between your UIM limit and the at-fault driver’s liability limit (how that gap is calculated varies).
- Excess-style approach: UIM may provide additional coverage above what the at-fault driver’s insurer pays, up to your UIM limit (again, rules vary).
Because this is state-specific, the best “QA check” is to confirm your state’s structure and then compare it to your declarations page limits and policy wording.
How to file a UM or UIM claim
The process is similar to most claims, but UM/UIM often involves more documentation because your insurer is stepping into a role the at-fault driver’s insurer normally plays.
- Get medical care and keep records.
- Document the crash (photos, witness info, police report if appropriate).
- Notify your insurer promptly, especially for hit-and-run scenarios.
- Track losses (medical bills, time missed from work, treatment plans).
- Cooperate with the investigation and respond to requests.
- Confirm limits and requirements on your declarations page and policy.
For the broader step-by-step flow, see: Car Insurance Claims Process: Steps That Real Claims Follow
Choosing UM and UIM limits
There’s no perfect number for everyone, but these principles help:
- Consider matching your liability limits: many drivers choose UM/UIM limits similar to their bodily injury liability limits.
- Plan for injury costs: serious injuries can create costs beyond what people expect (treatment, rehab, time off work).
- Think about your financial risk: UM/UIM is mainly about protecting your household if the at-fault driver can’t fully pay.
Common misunderstandings
- “I have health insurance, so I don’t need UM/UIM.” Health insurance may not cover lost wages, pain and suffering, or certain long-term needs.
- “UM and UIM are the same thing.” UM is for no insurance; UIM is for not enough insurance.
- “These cover my car automatically.” Property damage rules vary; collision coverage often handles repairs.
- “Hit-and-run always pays.” Many policies require prompt reporting and proof that another vehicle caused the crash.
FAQ
Is uninsured vs underinsured motorist coverage required?
It depends on your state. Some states require UM, some require insurers to offer it, and UIM rules also vary. Your declarations page will show whether you have UM/UIM and what limits apply.
Can UM apply if I’m not in my car?
Sometimes. Some policies extend UM/UIM protection to you or household members as pedestrians or cyclists, while others limit coverage to vehicle occupants. Check your policy definitions for who is an insured person.
Is UM/UIM the same as “full coverage”?
No. “Full coverage” isn’t a standardized insurance term. UM/UIM are specific coverages that focus on losses caused by drivers who can’t fully pay.
Important to know
Car Policy Answers is an independent educational website. We do not sell insurance, provide quotes, or recommend insurance companies.
This article is for general educational purposes only. Auto insurance rules vary by state, and coverage depends on your policy terms and limits. For guidance on your specific situation, consider speaking with your insurer or a qualified professional in your state.