Uninsured motorist (UM) coverage pays for your injuries (and in many policies, some property damage) when the at-fault driver has no liability insurance, or after a qualifying hit-and-run. Underinsured motorist (UIM) steps in when the at-fault driver has insurance, but their liability limits are too small for your medical bills. This guide covers UM/UIM basics and when to buy; claim steps live in How to file an auto insurance claim.
State rules differ: some states require UM, some make it optional with a signed rejection, and stacking rules vary. Read your declarations page; do not treat another state’s forum post as your law.
UM vs UIM in one table
| Coverage | Trigger | Typical payout focus |
|---|---|---|
| UM bodily injury | At-fault driver has $0 liability, or hit-and-run per policy rules | Your medical bills, lost wages, related damages up to your UM limit |
| UIM bodily injury | At-fault driver’s liability limit is exhausted and your damages exceed it | The gap up to your UIM limit (offset rules vary by state/insurer) |
| UM/UIM property damage (where offered) | Same triggers for vehicle damage | Repair/total-loss path subject to deductible and policy form |
UM/UIM is not collision. Collision pays your car after a crash regardless of the other driver’s insurance, subject to your deductible (Full coverage vs liability only).
When you need higher UM/UIM limits
Buy or raise UM/UIM when any of these are true:
- You live or commute where uninsured-driver rates are high (ask your agent for local context; rates change by metro).
- Your household has thin disability / sick leave, so a soft-tissue injury could wipe savings.
- Your liability limits are already 100/300 or higher and your UM/UIM sits at state minimum (example: 25/50). Match them when the form allows.
- You carry an umbrella and the carrier requires matching auto UM/UIM (Umbrella insurance policy; Umbrella and liability basics).
If you drive a paid-off beater with strong health insurance and a large cash reserve, you might accept lower UM property damage while still keeping solid UM bodily injury. That is a deliberate tradeoff, not a default.
Worked example: underinsured crash
Sam’s medical bills after a red-light crash total $85,000. The at-fault driver carries 25/50 liability. The other insurer tenders $25,000. Sam’s UIM limit is 100/300. After the other driver’s payment and any state offset rules, Sam’s UIM can cover a large share of the remaining medical gap (exact dollars depend on the policy form and liens). Without UIM, Sam would face the rest from health insurance, HSA, and personal funds.
Shop UM/UIM on the same stack you use elsewhere (Comparison-shop auto insurance). Deductibles on collision still matter for the car: Auto insurance deductibles.
What UM/UIM usually does not fix
- Your own at-fault crash (that is liability and collision).
- Every hit-and-run; some policies require a police report within a set window.
- Punitive damages or every type of pain-and-suffering claim (policy and state dependent).
- Gaps better filled by health insurance, disability coverage, or an umbrella.
Checklist
- Find UM and UIM limits on your declarations page.
- Compare them to your liability BI limits; raise UM/UIM toward parity if affordable.
- Ask whether property-damage UM is included or optional in your state.
- Confirm hit-and-run reporting deadlines with your carrier.
- Re-check limits when you add an umbrella or move states.
Educational only. Not an insurance quote or legal advice. UM/UIM definitions, stacking, offsets, and mandatory offers vary by state and insurer; confirm on your policy form and with a licensed agent.