Uninsured vs Underinsured Motorist Coverage Explained
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Last updated on November 21, 2025
By
Jane Taylor
— Insurance content contributor
When shopping for auto insurance, understanding the difference between uninsured vs. underinsured motorist coverage matters because both are designed to protect you from costs caused by other drivers—drivers who either have no insurance or not enough insurance. These coverages can help pay for injuries (and sometimes vehicle damage) when the at-fault driver can’t fully pay.
This guide breaks down how each coverage works, when it applies, common “gotchas” (like stacking rules and limit offsets), and how to choose limits that fit your risk level and budget. To see how these protections fit into a complete policy, review our Loya auto insurance coverage overview.
Disclaimer: This article is general information and not legal or financial advice. UM/UIM rules vary by state and carrier (including whether property damage is included, how limits apply, and how claims are calculated). Always confirm details with your state’s Department of Insurance and your policy documents.
Data snapshot (why UM/UIM can matter)
- In 2023, an estimated 15.4% of motorists—more than 1 in 7—were uninsured (rates vary widely by state). [1]
- In 2024, the average auto liability claim severity was $28,278 for bodily injury and $6,770 for property damage. [2]
- Motor-vehicle injury costs were estimated at $513.8 billion in 2023 (economic costs). [3]
Takeaway: even a “moderate” crash can exceed low liability limits—UM/UIM helps protect you when the other driver’s insurance can’t.
What Uninsured Motorist (UM) Coverage Is
Uninsured motorist (UM) coverage helps protect you if you’re hit by a driver who has no liability insurance (and in many states, it can also apply to certain hit-and-run situations, depending on policy language and state rules). [4]
UM most commonly pays for injury-related losses such as medical bills and lost wages, up to your UM limit. Some states and carriers also offer uninsured motorist property damage (UMPD), which can help pay to repair your vehicle, usually with its own rules and limits.
Practical note: UM is about the other driver having no insurance. If the other driver has insurance but their limits are too low, that’s where UIM comes in.
What Underinsured Motorist (UIM) Coverage Is
Underinsured motorist (UIM) coverage applies when the at-fault driver does have insurance, but their liability limit is too low to cover your covered losses.
After the other driver’s policy pays out up to their limit, UIM may help cover remaining eligible losses—up to your UIM limit—based on how your state calculates UIM benefits. In some states, UIM can work as an “add-on” up to your limit; in others, benefits can be reduced by the at-fault driver’s available liability limit. Always confirm how your state treats UIM. [4]
UM vs. UIM: The Key Differences
UM and UIM address different gaps. Many drivers carry both because you can’t predict which problem you’ll face on the road.
| Feature | Uninsured Motorist (UM) | Underinsured Motorist (UIM) |
|---|---|---|
| When it applies | At-fault driver has no insurance (and sometimes certain hit-and-run cases) | At-fault driver has insurance, but limits are too low |
| Main problem it solves | No liability coverage available from the other driver | Not enough liability coverage available from the other driver |
| What it may pay for | Often injuries; sometimes vehicle damage (UMPD) depending on state/policy | Often injuries; availability and calculation can vary by state/policy |
Two “Gotchas” That Affect How Much You Actually Get Paid
1) Stacked vs. non-stacked UM/UIM
In some states and policies, UM/UIM limits can be “stacked” (combined across vehicles/policies) or “non-stacked” (your stated limit is the max, regardless of vehicle count). Whether stacking is allowed (and how) depends on state law and policy terms. [4]
2) How UIM limits are calculated
UIM can be treated differently depending on the state (for example, whether UIM is reduced by the at-fault driver’s liability limit). This is why two drivers with the same “UIM limit” can receive different results across states. Always confirm the rules in your state and read your declarations page and endorsements. [4]
How Much UM/UIM Coverage Should You Carry?
A common starting point is choosing UM and UIM limits that match your bodily injury liability limits, then adjusting based on your budget and risk exposure. If you have savings, a home, or higher income, stronger limits may help protect you from medical and income-loss costs that quickly exceed minimum liability limits.
The easiest way to decide is to request quotes at multiple limit levels and compare the monthly difference. Many drivers are surprised that moving from low limits to stronger limits costs less per month than expected.
What to Do After a Crash With an Uninsured or Underinsured Driver
- Call for help and document the scene: photos, vehicle positions, damage, and injuries.
- File a police report when appropriate (especially for hit-and-run scenarios).
- Get witness information if anyone saw what happened.
- Notify your insurer promptly and ask specifically about UM/UIM claim steps and deadlines.
- Keep a folder of medical bills, wage loss documentation, repair estimates, and correspondence.
What Customers Say
Examples are illustrative and anonymized; individual outcomes vary by policy and state rules.
“I didn’t realize how quickly medical bills add up. Having UM/UIM in place meant I wasn’t relying only on the other driver’s low limits.”
“My agent explained stacking and how my limits applied. That clarification helped me choose coverage I could keep long-term.”
FAQ
What is the difference between uninsured and underinsured motorist coverage?
UM applies when the at-fault driver has no insurance (and sometimes certain hit-and-run cases). UIM applies when the at-fault driver has insurance, but their limits are too low to cover your covered losses.
Does UM/UIM cover damage to my car?
Sometimes. Some states/policies offer uninsured motorist property damage (UMPD), but availability and rules vary. Collision coverage is the most common way to protect your own vehicle after a crash, regardless of the other driver’s insurance status.
Is UM coverage required?
Requirements vary by state. Some states require UM, some require insurers to offer it, and some make it optional. Always confirm your state’s rules and review your policy documents.
Should my UM/UIM limits match my liability limits?
Many drivers start there because it keeps protection consistent. The right amount depends on your income, assets, healthcare costs, and how much risk you can afford to absorb.
Can my premiums increase after a UM/UIM claim?
It depends on the insurer and state rules. Any claim can affect pricing, but outcomes vary based on fault, claim history, and rating practices.
Conclusion
UM and UIM coverage help protect you from a risk you can’t control: other drivers who either have no insurance or not enough insurance. By understanding when UM vs. UIM applies, how limits and “stacking” can affect benefits, and choosing limits that match your real-world risk, you can build a more resilient policy.
Get Started
Ready to see how UM/UIM fits into your policy? Review options and compare quotes on our
auto insurance coverage explained page to compare coverage combinations that make sense for your budget.
References
- NAIC — Uninsured Motorists (IRC estimate: 15.4% uninsured in 2023; state variation).
- Insurance Information Institute (III) — Auto insurance facts & statistics (2024 average liability claim severity).
- National Safety Council — Injury Facts: Motor Vehicle (2023 injury costs).
- III — Background on compulsory auto insurance & uninsured motorists (state variability; stacking discussion).