Quick Answer
UM vs UIM: Uninsured motorist (UM) coverage pays when the driver who hits you has no insurance; underinsured motorist (UIM) pays when they have insurance but not enough to cover your damages. Both are separate from liability and from full coverage, and both typically cost $3-15/month depending on limits.
Most uninsured drivers by state (2023): Mississippi leads at 28.2%, then New Mexico (24.1%), Michigan (22.3%), Tennessee (21.3%), Missouri (20.7%), Florida (20.6%) and California (20.4%). The national average is 15.4%; the lowest is Maine at 5.7%. Source: Insurance Research Council, Uninsured and Underinsured Motorists: 2017-2023.
The Third Coverage Decision
Most coverage discussions focus on two choices: liability-only vs full coverage. But there is a third, separate decision that most competitor sites treat as a footnote: uninsured and underinsured motorist coverage.
UM (Uninsured Motorist) pays when the driver who hits you has no insurance at all. UIM (Underinsured Motorist) pays when the driver who hits you has insurance but not enough to cover your total damages. Both pay for your medical bills, lost wages, and pain and suffering -- not covered by liability or full coverage in an at-fault crash caused by someone else.
UM vs UIM vs UMPD
| Coverage | When It Pays | What It Covers | Typical Cost |
|---|---|---|---|
| UM (Uninsured Motorist) | Other driver has NO insurance | Your medical bills, lost wages, P&S | $3-6/mo (25/50) |
| UIM (Underinsured Motorist) | Other driver's limits too low | Your excess damages above their payout | $5-8/mo (100/300) |
| UMPD (UM Property Damage) | Uninsured driver damages your car | Your vehicle repairs | $2-4/mo (25 states only) |
Why UM/UIM Matters Most When You Drop Full Coverage
When you carry full coverage (collision + comprehensive), collision pays for your car's damage whether or not the other driver is insured. Drop full coverage and you lose that backstop. If an uninsured driver totals your $8,000 car, you have no recourse unless you carry either UM with a property damage component (UMPD) or can afford to absorb the loss directly.
In Mississippi -- where an estimated 28% of drivers are uninsured -- the expected probability that the driver who totals your car is uninsured is genuinely high. In states like Maine (about 6% uninsured) the risk is much lower. UM/UIM is especially critical in the high-risk states below.
Uninsured Driver Rate by State (Selected States)
| State | UNINSURED % | UM/UIM Required |
|---|---|---|
| Mississippi | 28.2% | Optional |
| New Mexico | 24.1% | Optional |
| Michigan | 22.3% | Optional |
| Tennessee | 21.3% | Optional |
| Missouri | 20.7% | Required |
| Florida | 20.6% | Optional |
| California | 20.4% | Optional |
| Colorado | 19.7% | Optional |
| Washington | 19.1% | Optional |
| Ohio | 18.5% | Optional |
| Delaware | 17.6% | Required |
| Maryland | 16.9% | Required |
| Alabama | 16.8% | Optional |
| Kentucky | 14.1% | Optional |
| Alaska | 12.5% | Optional |
| Rhode Island | 12.4% | Required |
| Arkansas | 12.1% | Optional |
| Vermont | 11.8% | Required |
| New York | 8.6% | Required |
| Maine | 5.7% | Required |
Source: Insurance Research Council (IRC), Uninsured and Underinsured Motorists: 2017-2023 (published March 2025), 2023 figures. National average 15.4%. Covers selected states with notable high or low rates; see the full state comparison table for all 50 states.
How Much UM/UIM Costs and What Limits to Buy
UM/UIM coverage is priced based on your chosen limits. The recommendation is to match your UM/UIM limits to your bodily injury liability limits. If you carry 100/300 BI liability, you should carry 100/300 UM/UIM.
| UM/UIM Limits | Typical Monthly Cost |
|---|---|
| 25/50 | $3-6/mo |
| 50/100 | $5-9/mo |
| 100/300 | $10-15/mo |
| 250/500 | $18-25/mo |
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