Last Updated on August 18, 2026
Written by licensed insurance agent Andy walker
Reviewed by the Alias Insurance editorial team.
Uninsured motorist coverage and underinsured motorist coverage protect you from two different gaps caused by another driver. Uninsured motorist coverage, called UM, may pay when an at fault driver has no liability insurance. It may also apply to a hit and run driver who cannot be found. Underinsured motorist coverage, called UIM, may pay when the at fault driver has insurance, but that plan cannot pay all of your valid loss.
Both are claims under your own auto plan. They do not pay because you caused a crash. You must show that the other driver was at fault and that your loss fits the plan. Bodily injury cover may pay for care, lost pay, pain, and death related loss allowed by state law. Property damage cover may pay for your car and other assets, but states do not sell or require it in the same way.
Use one quick test. If the driver who hit you had no active liability plan, look first at UM. If that driver had a plan but its limit ran out before your loss was paid, look at UIM. If the other driver had enough cover, neither UM nor UIM should be needed for that claim.
Limits, claim shares, hit and run rules, offsets, and stacking differ by state and plan. Some states require UM. Some require firms to offer it. Others make it optional. UIM may follow a different rule in the same state. Check your declarations page and any signed waiver before you assume either one is part of your plan.
What is the main difference between UM and UIM?
| Question | Uninsured motorist coverage | Underinsured motorist coverage |
| What starts the claim? | The at fault driver has no usable liability plan or is unknown after a valid hit and run. | The at fault driver has a liability plan, but its limit is too low for the valid loss. |
| Who handles it? | Your own auto firm handles the UM claim. | Your own auto firm handles the UIM claim after it checks the other plan and payout. |
| What may it pay? | Valid harm and, where bought or required, car and property loss. | Valid harm and, in some states and plans, car and property loss above the other limit. |
| Does it pay for your fault? | No. The other driver must normally be legally responsible. | No. The other driver must normally be legally responsible. |
| Does a claim share apply? | It may apply to car damage. State and plan rules control. | It may apply to car damage where that cover is sold. Injury rules can differ. |
The National Association of Insurance Commissioners gives the same core test. UM applies after a crash with an uninsured or hit and run driver. UIM applies when an at fault driver’s plan cannot pay the loss in full. Your declarations page must still show that you bought the cover and state its limit.
The risk is not rare. The NAIC said 15.4 percent of drivers, about one in seven, were uninsured in 2023. The rate ran from 5.7 percent in Maine to 28.2 percent in Mississippi. A driver with insurance can also have a low state minimum limit.
What do UMBI, UIMBI, UMPD, and UIMPD mean?
Uninsured motorist bodily injury
UMBI may pay for harm to you, family members who live with you, and people in a listed car. It may also protect you while walking or riding a bike. The plan and state law define who is insured.
Underinsured motorist bodily injury
UIMBI may pay for valid harm left after the other driver’s injury limit is used. Your UIM limit, prior pay, shared fault, plan terms, and proof can cut the amount.
Uninsured motorist property damage
UMPD may pay for your car or insured assets when a driver with no plan causes the crash. California says its UMPD applies if the driver is known and the insured has no collision cover. Texas uses a 250 dollar claim share.
Underinsured motorist property damage
UIMPD may pay when the other driver’s property limit cannot cover your car loss. Some states sell it. Others limit UM and UIM to injury claims. Pennsylvania and Nevada state guides say their UM and UIM do not pay for vehicle damage.
How does uninsured motorist coverage work?
A UM claim starts with proof that the other driver caused the crash and had no usable liability plan. That can mean no plan, a lapsed plan, or a denial that leaves no cover. Some plans also address an insolvent firm. Read the plan’s definition of an uninsured vehicle.
Example: A driver with no plan runs a red light and causes 48000 dollars in valid harm. You have 100000 dollars of UMBI per person. UM may pay up to 48000 dollars. It does not pay the full limit just because the limit exists. The firm pays a valid loss, not an automatic award.
A hit and run can lead to a UM claim, but quick proof matters. Call police, take photos, save video, get witness details, and tell your firm soon. Some claims require car contact, a police report, fast notice, or proof from another person. Follow this guide to filing a claim after a hit and run and the duties in your plan.
Does your personal car insurance follow you?
It may. Many personal policies protect the named driver in a car that person does not own. Each part can differ. Liability may reach more cars than collision. Use beyond the dealer’s consent may not be covered.
Call your insurer before you drive a costly car, sports car, or large truck. Ask these exact questions:
- Does my liability coverage apply while I test drive a dealer owned car?
- Is that coverage primary or excess over the dealer’s policy in this state?
- Does my collision coverage extend to the test car?
- What deductible and limit would apply to damage to that car?
- Are there limits for business use, racing, use away from public roads, or a car given for regular use?
- Will you confirm the answers by email or cite the policy?
A test drive may not count as a rental. Ask about the planned use and exact car.
How does underinsured motorist coverage work?
A UIM claim starts when the at fault driver has a plan, but its limit is not enough. The gap may come from a low per person limit, a low total limit, several hurt people, several damaged cars, or one costly loss.
Suppose your valid harm is 120000 dollars. The other driver has a 25000 dollar injury limit. You have 100000 dollars of UIM. A plan may offset the first payout, as New York SUM does. The 25000 dollars may cut your UIM funds to 75000 dollars. Both firms could then pay no more than 100,000 dollars. A 20000 dollar gap would remain.
Maryland shows a different choice. It adds enhanced UIM to new plans unless the buyer signs an opt out form. A person with an old plan can ask to add it. Enhanced UIM can be added to the other driver’s limit, up to the UIM limit and the valid loss. Never use one state’s math for a claim in another state.
Do not sign a release before your UIM firm checks the planned payout. Your firm may have a right to seek funds from the at fault party. Washington tells claimants to notify their firm before they agree to a deal while the firm seeks recovery. Ask for written consent.
How do payment limits change the result?
| Example loss | Available coverage | Possible claim path |
| 60000 dollars of harm caused by a driver with no plan | 100000 dollars of UMBI per person | UM may pay up to the proven 60000 dollar loss, subject to state law and the plan. |
| 120000 dollars of harm, with 25000 dollars from the other driver | 100000 dollars of UIM with an offset | The other firm may pay 25000 dollars. UIM may have up to 75000 dollars left. |
| 120000 dollars of harm, with 25000 dollars from the other driver | 100000 dollars of enhanced UIM that can be added | The other firm may pay 25000 dollars. Enhanced UIM may pay up to 95000 dollars more. |
| 18000 dollars of car loss caused by a driver with no plan | 25000 dollars of UMPD with a 250 dollar claim share | UMPD may pay 17750 dollars if the full loss is valid and no other cut applies. |
These figures are examples, not promises. A per person limit caps one person’s injury claim. A per crash limit caps all injury claims from that crash. Property damage has its own limit. Read how a car crash claim can exceed insurance limits before you pick the lowest amount offered.
What losses can UM and UIM pay?
Injury benefits may pay care bills, future care, lost wages, pain, and death related loss allowed by law. You must link the harm to the crash and prove the amount. Shared fault and limits can cut the payout.
Property benefits may pay to fix or replace the car, cover loss of use, or pay for assets in it. Texas also lists rental cost and lost car value. Other states use more narrow rules.
UM and UIM do not pay for wear, normal repairs, excess loan debt, or loss not tied to the crash. They do not replace liability cover for harm you cause.
How do state rules change the coverage?
State law can change what you must buy. It can also change property cover, claim shares, stacking, hit and run proof, and UIM math. These state examples show why there is no one rule for the whole country.
- California makes firms offer UM and UIM. A buyer can sign a waiver. Its guide treats UMBI, UIM, UMPD, and a collision claim share waiver as separate choices.
- Texas makes firms offer UM and UIM. A buyer who says no must do so in writing. It can pay for harm, car repair, and hit and run loss. The claim share is 250 dollars.
- South Carolina requires UM at state minimum limits. The claim share is often 200 dollars. Firms must offer UIM, but purchase is not required.
- New York has basic UM injury cover. Optional SUM can raise that cover and apply to a low limit driver. Funds paid by the other plan offset the SUM limit.
- Pennsylvania lets a buyer stack UM and UIM. Stacked cover applies unless the buyer rejects it. The state guide says its UM and UIM do not pay for property.
- Nevada makes firms offer UM and UIM up to the liability limits. A buyer can say no. Its guide lists injury cover, not car damage cover.
Ask a licensed agent for the current state form. Your state insurance department can confirm the law and check the firm’s license.
What is stacking, and why does it matter?
Stacking can join UM or UIM limits from more than one car or plan. If a Pennsylvania plan has 50000 dollars of UIM for each of three cars, stacked limits may reach 150000 dollars. The plan, person, car, loss, and state law still control the claim.
Some states let plans bar stacking or use a written waiver. Ask if a quote is stacked, if household plans can join, and which form states your choice.
How are UM and UIM different from collision and no fault benefits?
Collision cover can pay for your car after an impact and often has a claim share. UMPD may have a lower claim share, but it may need proof that the other driver had no plan. Collisions can start repair while firms review faults.
Medical payments cover and PIP can pay care bills before fault is set. PIP may pay part of lost income. UM and UIM need proof of the other driver’s fault. PIP may pay first in a no fault state.
How do you file an UM or UIM claim?
- Make the scene safe. Call 911 for harm, road risk, or a hit and run. Follow the report law where the crash took place.
- Gather proof. Take photos of each car, the road, harm, plates, and insurance cards. Save video and get witness names.
- Tell your firm soon. Ask for the claim number, claim rep, and needed forms.
- Open a claim with the other firm when the driver is known. Ask for proof of the live plan and its limits.
- Prove the loss. Send care records, bills, wage proof, repair bids, rental bills, photos, and other asked for files.
- Protect your rights. Do not release the other driver or take a final limit check until you meet your firm’s notice and consent rules.
- Ask for a written choice. It should state the cover, limit, claim share, fault view, payout math, and each cut.
Your own firm handles a UM or UIM claim, but it still reviews fault and loss. Keep copies. If the firm says no, compare its letter with the plan and read what to do after an auto insurance claim denial. You may also call the state insurance department or a lawyer.
How much UM and UIM coverage should you consider?
Start with your bodily injury liability limit. Then ask if the same UM and UIM limits are sold. A driver with 250000 dollars of liability but 25000 dollars of UIM gives others more cover than the household gets from a low limit driver.
Compare quotes with the same limits and stacking choice. Check injury cover, property cover, hit and run rules, claim shares, and named people. Ask if the other payout cuts your UIM limit.
Drivers with a family, frequent guests, or long drives may want to ask about higher limits. The required minimum car insurance may meet the law yet leave a large unpaid loss.
.What common mistakes can delay or reduce a claim?
- Assuming UM and UIM are the same without checking the trigger
- Waiting too long to report a hit and run or to preserve video
- Fixing or selling the car before the firm can inspect it
- Taking the other firm’s limit without telling the UIM firm
- Using one state’s rules to predict a claim in another state
- Leaving out a hurt person or damaged asset before limits are split
- Keep reports, photos, bills, letters, and call notes in one claim file.
Frequently Asked Questions
No. UM applies when the at fault driver has no usable liability plan or is unknown after a valid hit and run. UIM applies when that driver has a plan, but its limit is too low for the valid loss.
It often can, but state and plan rules vary. Tell the police and your firm soon. Save video, witness names, and photos. Some claims need car contact or more proof.
You may want it if it has a lower claim share, rental pay, or another state benefit. Some states limit UMPD when collision is on the plan. Compare both choices.
Not at once. Your firm must check fault, the loss, and the other limit. You may need consent before you take the other firm’s last payout. UIM pays only a valid amount within its own limit.
It can in some states and plans. The cover may follow a named person or a family member outside the insured car. The plan’s insured person rule and the crash facts control the answer.
State law controls. Some states require one or both. Some require an offer and a signed rejection. Others let you choose. Keep a copy of each rejection, limit choice, or stacking waiver.
Key Takeaways
- UM applies when an at fault driver has no usable liability plan.
- UIM applies when an at fault driver’s liability limit is too low.
- Injury and property cover are separate and vary by state.
- The other payout may cut the UIM limit, or state law may allow added cover.
- Hit and run rules, claim shares, stacking, and waivers need a plan check.
- Report the crash soon, save proof, and get consent before you sign a release.
Read your declarations page before the next renewal. Compare the same limits, claim shares, and stacking choices. Ask a licensed professional to explain each gap. Alias Insurance can help you compare car insurance quote options from providers in your area, so you can judge cover as well as price.
Sources and References
- NAIC guide to what auto insurance covers
- NAIC uninsured motorists overview and 2023 estimate
- California Department of Insurance auto coverage guide
- Texas Department of Insurance auto insurance guide
- South Carolina Department of Insurance automobile coverage guide
- New York Department of Financial Services auto insurance resource center
- Pennsylvania Insurance Department auto insurance guide
- Nevada Division of Insurance consumer auto guide
- Maryland Insurance Administration enhanced UIM guide
- Washington Office of the Insurance Commissioner claim guidance
