Updated July 2026
What Is Uninsured and Underinsured Motorist Coverage Insurance?
Uninsured motorist coverage (UM) and underinsured motorist coverage (UIM) protect you when another driver causes an accident but lacks adequate insurance to pay for your injuries or vehicle damage. UM applies when the at-fault driver has no insurance at all. UIM kicks in when their liability limits fall short of your actual costs. Your own insurer pays the claim up to your UM/UIM policy limits, then pursues recovery from the at-fault party.
- You're rear-ended at a stoplight by a driver with no insurance. You have $8,000 in medical bills and $5,000 in vehicle damage. The at-fault driver has no coverage to pay your claim. Your UM coverage pays both amounts up to your policy limits. Without UM, you'd file a lawsuit and likely collect nothing—most uninsured drivers lack assets to satisfy a judgment.
- Another driver runs a red light and T-bones your car. Your medical bills total $75,000, but the at-fault driver carries only Montana's minimum $25,000 per-person bodily injury limit. Their insurer pays the $25,000 maximum. If you carry $100,000 in UIM coverage, your insurer pays the remaining $50,000. Without UIM, you absorb the $50,000 shortfall or pursue the driver personally—a process that rarely recovers full damages.
- A driver sideswiped your vehicle on the highway and fled the scene. You have $4,200 in repair costs and no way to identify the other driver. Your UM coverage treats this as an uninsured motorist claim and pays for the damage, minus your deductible. Collision coverage would also pay here, but UM often carries a lower or zero deductible, saving you out-of-pocket cost.
Who Needs Uninsured and Underinsured Motorist Coverage Insurance?
Drivers in Montana should strongly consider UM/UIM if they carry assets worth protecting—home equity, retirement accounts, or significant savings—since a serious accident with an uninsured driver could force you to tap those assets to cover medical bills and lost wages. It's also critical if you finance or lease your vehicle, as collision coverage alone won't cover the gap between your car's value and what you owe if the at-fault driver is uninsured. Families with multiple drivers or high medical costs benefit most, since UM covers all occupants in your vehicle at the time of the crash.
Match your UM/UIM limits to your liability limits as a baseline—if you carry $100,000 in liability to protect others, you should carry at least $100,000 in UM to protect yourself. Then adjust based on your health insurance: if your health plan has a $10,000 deductible or high coinsurance, increase UM to cover that gap. The cost difference between minimum and robust UM coverage is small relative to the financial exposure you're eliminating.
How Much Does Uninsured and Underinsured Motorist Coverage Insurance Cost?
UM/UIM coverage typically adds $8 to $18 per month to your premium, or roughly $96 to $216 annually, depending on the limits you select and your driving profile.
- Coverage limits—higher UM/UIM limits cost more, but the incremental cost from $25,000 to $100,000 is often under $5 per month.
- Stacked versus unstacked coverage—stacked UM/UIM multiplies your per-vehicle limit across all vehicles on your policy, increasing both protection and cost.
- Your ZIP code's uninsured driver rate—areas with higher percentages of uninsured motorists see slightly elevated UM premiums due to increased claim frequency.
- Claim history—prior UM claims can raise your rate at renewal, though less severely than at-fault liability claims.
- Bundling with liability limits—carriers often discount UM/UIM when you carry liability limits equal to or higher than your UM limits.