Uninsured & Underinsured Motorist Coverage (UM/UIM): The Complete Guide [2026]

Table of Contents

• 1. What UM vs. UIM Coverage Is and the Gap They Fill
• 2. Stacking UM/UIM By State
• 3. “Setoff” vs. “Add-On” (Difference in How UIM Pays)
• 4. When to File: Timing and Statutes of Limitation
• 5. Phantom Vehicle and Hit-and-Run UM Claims
• 6. UIM-Specific Challenges: Arbitration, Bad Faith, Consent-to-Settle
• 7. State Minimum vs. Realistic UM/UIM Limits
• Common UM/UIM Mistakes to Avoid
• What to Do Next: A Checklist

1. What UM vs. UIM Coverage Is and the Gap They Fill

Uninsured Motorist (UM) and Underinsured Motorist (UIM) coverage are distinct yet complementary parts of your auto insurance policy designed to protect you when another driver is at fault but lacks sufficient insurance.

Uninsured Motorist (UM) Coverage

UM coverage steps in when the at-fault driver is legally considered uninsured. This can occur in several common scenarios:

• The at-fault driver has no liability insurance whatsoever.
• The at-fault driver is a hit-and-run phantom driver, meaning they cannot be identified (covered in many states).
• The at-fault driver's liability insurer denies coverage or becomes insolvent (expressly treated as “uninsured” in some states, like Georgia).

For example, Illinois requires UM bodily injury limits of at least $25,000 per person and $50,000 per accident for policies issued in the state. 215 ILCS 5/143a; the state Department of Insurance confirms these minimums.¹

Underinsured Motorist (UIM) Coverage

UIM coverage applies when the at-fault driver has some liability insurance, but not enough to cover your total damages. The Illinois Department of Insurance describes “gap” UIM as paying “the difference between your UIM limits and the liability limits of the at-fault driver, if lower than your UIM limits.”²

UM/UIM coverage fills a critical gap because even though every state requires or strongly encourages liability coverage, a substantial percentage of drivers either carry no insurance or carry bare minimum limits (often 25/50 or 30/60) that are inadequate for serious injuries. UM/UIM effectively stands in for what you would have recovered from the at-fault driver had they carried reasonable liability limits.³

2. Stacking UM/UIM By State

“Stacking” refers to combining UM/UIM limits to increase the total available coverage. There are two primary forms:

1. Inter-policy stacking: Adding limits from multiple policies, such as your own policy plus a household member’s policy.
2. Intra-policy stacking: Multiplying limits by the number of vehicles insured under the same policy.

States approach stacking in three main ways:

(a) States that Generally Allow Stacking (Absent Clear Anti-Stacking Language)

Many courts presume stacking is allowed unless clearly and unambiguously excluded in the policy. Some statutes even affirmatively allow stacking.

• Pennsylvania: Stacking is the default; insureds must sign a valid waiver to reject stacking. 75 Pa. Cons. Stat. § 1738.
• Georgia: Georgia law allows “add-on” UM that stacks on top of liability coverage and on other UM policies. O.C.G.A. § 33-7-11(b)(1)(D)(ii) (post-2009).
• Missouri: Often allows stacking if the policy is ambiguous; see, for example, Ritchie v. Allied Prop. & Cas. Ins. Co., 307 S.W.3d 132 (Mo. 2009).

(b) States That Permit Anti-Stacking Clauses (And Many Policies Use Them)

Many states allow insurers to prohibit stacking through clear policy wording. Whether stacking is available depends heavily on the specific policy language.

• Illinois: Anti-stacking language is generally enforceable if clear and unambiguous. See, for example, Hobbs v. Hartford Ins. Co. of the Midwest, 823 N.E.2d 561 (Ill. 2005).
• Texas: Insurers may include anti-stacking clauses; stacking is frequently barred by contract language. See Texas Ins. Code § 1952.101 et seq.
• Florida: Allows “stacked” versus “non-stacked” UM; the choice affects premium and stacking rights. See Fla. Stat. § 627.727(9).

(c) States That Heavily Restrict or Effectively Prohibit Stacking

Some states statutorily limit stacking, especially intra-policy stacking, or treat UM as a “per accident” cap that cannot be multiplied.

• New York: Stacking is generally not permitted beyond the highest single limit applicable unless the policy structure allows it; N.Y. Ins. Law § 3420(f); see also Government Emps. Ins. Co. v. Kligler, 319 N.E.2d 842 (N.Y. 1974) (enforcing anti-stacking).
• New Jersey: Anti-stacking policy provisions are widely enforced; see N.J.S.A. 17:28-1.1.

Because stacking rules are intensely state-specific and often turn on contract wording, the starting point is always your state’s UM/UIM statute and the specific policy language, including “other insurance,” “limits of liability,” and “anti-stacking” clauses.

3. “Setoff” vs. “Add-On” (Difference in How UIM Pays)

A key distinction in UIM coverage is whether it operates as **gap/offset** coverage or **add-on** coverage.

Gap / Setoff States

In a setoff scheme, your UIM limits are reduced by the at-fault driver’s liability limits (not necessarily the amount actually collected, in many states).

Example (Illinois – classic gap approach):

• You have UIM limits: $100,000 per person.
• At-fault driver has liability: $50,000 per person.
• Under 215 ILCS 5/143a-2(4), UIM is triggered only if the at-fault driver’s limits are less than your UIM limits, and the maximum UIM available is the difference.
• Total bodily injury coverage available to you: $50,000 liability + up to $50,000 UIM = $100,000.

Other setoff/gap jurisdictions include Indiana, Ohio, and many others, often by statute.

Add-On States

In an add-on regime, your UIM limits are payable on top of what the at-fault driver carries, up to your policy limits, without subtracting the liability amount.

Example (Georgia post-2009):

• O.C.G.A. § 33-7-11(b)(1)(D)(ii) creates “add-on” UM (“excess” UM) if selected.
• You have UM/UIM: $100,000.
• At-fault driver has liability: $50,000.
• You may collect $50,000 from the liability carrier plus up to $100,000 from your UM/UIM, for a total of $150,000 (subject to proof of damages). No offset.

Some states allow the consumer to choose between “reduced/gap” and “add-on” UM/UIM (Georgia, Florida). In others, the regime is fixed by statute.

4. When to File: Timing and Statutes of Limitation

UM/UIM timing is tricky because it involves two layers:

1. The underlying **tort claim** against the at-fault driver (governed by your state’s personal injury statute of limitations; often 2 or 3 years).
2. The **contract claim** against your own insurer for UM/UIM benefits (often a longer contract limitations period, but not always).

General Patterns

• Personal injury tort limitations: 2-3 years in many states (e.g., Illinois – 2 years, 735 ILCS 5/13-202; Texas – 2 years, Tex. Civ. Prac. & Rem. Code § 16.003).
• Contract/UM limitations: often 4-6 years for written contracts, but policies frequently include shorter contractual “suit limitations” periods (e.g., 2 or 3 years from date of accident, or from when UM coverage was “breached”).

In several states, courts treat UM/UIM actions as either contract claims subject to the contract statute of limitations (e.g., Minnesota; see Schwartz v. line of cases) or as hybrid claims where the tort limitation governs notice or the underlying claim, while the contract limitation governs suit against the insurer.

Important Case Example – Minnesota: Schmidt v. Clothier

Schmidt v. Clothier, 338 N.W.2d 256 (Minn. 1983), established a detailed procedure for UIM, including timing and notice requirements. When the liability insurer tenders its policy limits to settle, the UIM carrier must be given notice and an opportunity (usually 30 days) to:

• Substitute its own payment to preserve subrogation rights; or
• Allow the insured to accept the settlement.

Failure to follow this procedure can forfeit UIM rights. Many states have adopted Schmidt-style notice and consent procedures either by statute or case law (including New Jersey’s Longworth process, discussed below).

Practical implication:

You usually must preserve the underlying tort claim within the ordinary personal injury statute of limitations. You must also comply with policy notice requirements (often “prompt” or within a stated time), any contractual “suit within X years” clause, and special statutory procedures (Schmidt/Longworth style notice and consent to settle).

5. Phantom Vehicle and Hit-and-Run UM Claims

UM often covers injuries caused by unknown or hit-and-run drivers. States impose varying **corroboration** requirements to prevent fraud.

Typical Requirements

Common statutory or policy requirements include:

• Physical contact requirement: Some states require actual physical contact between the phantom vehicle and the insured’s vehicle to trigger UM coverage in a hit-and-run (e.g., California Ins. Code § 11580.2(b)(1)).
• Independent corroboration: If there is no physical contact, some states require an independent witness or other evidence corroborating the insured’s account.
• Prompt reporting: Many policies require reporting the hit-and-run to police within 24 hours or a short period.

Examples:

• Texas: UM/UIM must cover hit-and-run accidents, but courts enforce policy requirements for corroboration and prompt reporting. Tex. Ins. Code § 1952.101; see also cases like Latham v. Mountain States Mut. Cas. Co., 482 S.W.2d 655 (Tex. Civ. App. 1972) (requiring corroborating evidence).
• New York: MVAIC and UM claims generally require proof of physical contact or corroborated testimony. See N.Y. Ins. Law § 5217 (hit-and-run requirements).
• Georgia: Defines uninsured motor vehicle to include hit-and-run vehicles, but older case law applied a “physical contact” rule; later statutory amendments and decisions have somewhat softened these requirements; see O.C.G.A. § 33-7-11(b)(2).

Because the details vary sharply, it matters a lot whether the state follows a strict “physical contact” requirement, a flexible “corroboration” approach, or a more claimant-friendly rule allowing circumstantial proof. Failure to satisfy these conditions can bar a UM claim even if liability is otherwise clear.

6. UIM-Specific Challenges: Arbitration, Bad Faith, Consent-to-Settle

UIM/UM claims are contract claims against your own insurer, but they involve tort-style issues (fault, damages). Three recurring issues are particularly important:

(a) Arbitration vs. Litigation Clauses

Many UM/UIM policies contain clauses requiring arbitration of the insured’s entitlement to damages from the uninsured/underinsured motorist and the amount of damages.

• Some states broadly enforce UM/UIM arbitration clauses (e.g., New York – N.Y. Ins. Law § 5106(b) and 11 NYCRR 65; New Jersey’s UM is often arbitrated by policy).
• Others limit arbitration or allow the insured to elect court.

Points of friction include arbitration deadlines shorter than standard court limitations, limited discovery compared to litigation, and less predictable “case law” because awards are often not published.

(b) Bad Faith and Unfair Claims Practices

Because the UM/UIM insurer is your own carrier, a tension arises: the insurer owes you duties as an insured, but stands in an adversarial position as if it were the at-fault driver’s insurer. Bad faith UM/UIM claims may arise from unreasonable delays in evaluating clear liability/coverage, low-ball offers in the face of obvious, well-documented damages, or refusal to investigate or consider evidence.

• Illinois: Section 155 of the Illinois Insurance Code (215 ILCS 5/155) allows fee-shifting penalties for “vexatious and unreasonable” delay or denial.
• Texas: Chapters 541 and 542 of the Texas Insurance Code (unfair settlement practices, prompt payment of claims) and common law bad faith apply, but UIM has unique timing issues; see Brainard v. Trinity Universal Ins. Co., 216 S.W.3d 809 (Tex. 2006) (UIM insurer’s obligation generally arises only after tort liability and damages are established).

7. State Minimum vs. Realistic UM/UIM Limits

Understanding the difference between statutory minimums and realistic coverage needs is crucial.

Typical Statutory Minimums (Examples)

• Illinois: Liability minimum: 25/50 bodily injury; UM BI must be at least 25/50 and is mandatory. UIM is required when UM is purchased above minimum limits. 625 ILCS 5/7-601; 215 ILCS 5/143a, 143a-2; see also Illinois DOI.¹
• Georgia: UM must be offered in at least 25/50 for BI and $25,000 property damage. O.C.G.A. § 33-7-11(a)(1)(A). Insured may reject or choose lower limits in writing.⁶
• Texas: Liability minimums 30/60/25; UM/UIM must be offered but can be rejected in writing. Tex. Ins. Code § 1952.101.

These minimums are often grossly inadequate for serious injuries. A single helicopter transport and a few days in a trauma center can easily exceed $100,000. For comprehensive protection, consider UM/UIM limits that match or exceed your liability limits, ideally $250,000/$500,000 or higher, especially if you have significant assets to protect. The cost difference for higher limits is often minimal compared to the financial devastation a serious accident with an underinsured driver can cause.