Most families think about auto coverage in terms of “their driver, their car.” The driver causes an accident — liability pays the other party. The driver’s car gets hit — collision pays for the repair. This framing is correct as far as it goes. But the highest-stakes claim category for families — uninsured and underinsured motorist coverage — is about the empty seats next to you. It’s about what happens when someone else causes an accident that injures your family, and they either have no insurance or not enough of it.

What UM/UIM Actually Covers

Uninsured motorist (UM) coverage pays for your injuries — and your passengers’ injuries — when an at-fault driver either has no insurance or leaves the scene. Underinsured motorist (UIM) coverage pays when the at-fault driver has insurance, but their liability limits are too low to cover the actual medical costs, lost wages, and related damages your family sustains.

Neither UM nor UIM is about your car. They’re about your body, and the bodies of every person in your vehicle at the time of a crash. A $30,000 UIM policy may cover a single broken leg with follow-up surgery. It doesn’t cover a spinal injury, a brain injury, or months of rehabilitation for multiple family members. The gap between what the at-fault driver’s policy pays and what the actual harm costs comes out of your UM/UIM limits — and then, if those are exhausted, out of your own pocket.

UM coverage also typically includes a provision for hit-and-run incidents where the responsible driver cannot be identified. If someone runs a red light, hits your car, and drives away, there’s no liability coverage to collect from. Your UM policy is what fills that gap.

Why State Minimums Fall Short

Most states require drivers to carry a minimum level of liability insurance — the coverage that pays the other party when you cause an accident. Those minimums are often shockingly low by modern medical cost standards. A $25,000 bodily injury limit — the minimum in many states — covers less than one night in an ICU plus emergency stabilization in most metro areas.

The problem compounds when the at-fault driver is carrying those same minimums. Their $25,000 is exhausted quickly against real injuries. Your UIM coverage is supposed to bridge the gap, but only up to your own UIM limit — and if you’re carrying the same low minimums as state law requires, you have very little bridge to work with.

The standard recommendation in the industry: carry UM/UIM limits that match your liability limits, and carry liability limits well above the state minimum. A $100,000/$300,000 bodily injury liability policy paired with matching UM/UIM limits provides meaningful protection. A $25,000/$50,000 minimum limit policy with the state minimum UM/UIM does not.

Stacking, and Where It’s Allowed

“Stacking” refers to adding the UM/UIM limits from multiple vehicles on your policy together for a single claim. If you have three vehicles on a policy with $100,000 UIM per vehicle, a stacking policy would allow you to combine those limits to $300,000 for a single incident involving any one of those vehicles.

Stacking is permitted in about half of U.S. states and prohibited in the other half. Where it’s available, it’s typically purchased as an explicit endorsement — you have to opt in. The premium increase for stacking is usually modest (10–25%) relative to the coverage expansion.

In states that don’t permit inter-vehicle stacking, some carriers allow “intra-vehicle” stacking — applying your UM/UIM limit per person in a multi-person accident rather than once per incident. Ask your agent specifically about stacking availability in your state; it’s one of those benefits that exists quietly and is rarely volunteered.

A Right-Sized UM/UIM Number

The right UM/UIM limit for a family isn’t a fixed number — it depends on the number of people who regularly ride in your vehicles, your household’s income level (because lost wages are a component of the claim), and your existing health insurance coverage.

Families with robust health insurance that covers accident-related injuries, short-term disability coverage that addresses lost wages, and smaller households may find $100,000/$300,000 UM/UIM limits adequate. Families with high-deductible health plans, no disability coverage, and multiple frequent passengers should consider $250,000/$500,000 or more.

A useful benchmark: multiply the number of people who regularly ride in your primary vehicle by $100,000. That’s a rough floor for your UIM per-occurrence limit. It’s not actuarially precise, but it’s the right order of magnitude for a family thinking about protecting its passengers.

What to Do This Week

• Pull your current policy and locate your UM/UIM limits. They’re typically listed on the declarations page separately from your liability limits. If you’re carrying the state minimum, call your agent and ask for a quote to double it.
• Ask your agent whether stacking is available in your state. If it is, ask for the incremental cost of adding the stacking endorsement.
• Consider your household’s health insurance deductible and whether it would leave a significant out-of-pocket gap after a serious accident. UM/UIM coverage fills that gap when it’s caused by an underinsured driver.
• If you’re near the end of a policy period, don’t wait until renewal to make this change — you can adjust UM/UIM limits mid-term at most carriers.

Ready to put this to work? Pull your declarations page and compare your UM/UIM limits against your liability limits — they should match. If they don’t, run a quote to see what it costs to close that gap.