UM/UIM is the insured person's own gap protection

Liability insurance protects against damages an insured causes to others. UM/UIM works in the opposite direction: it is first-party coverage purchased to protect insured persons when the responsible motorist has no liability insurance or not enough liability insurance to cover the proved loss.

UM

Uninsured motorist

UM addresses covered bodily injury or death caused by a motorist whose required liability coverage is absent or who falls within another qualifying uninsured-motorist situation.

UIM

Underinsured motorist

UIM addresses the gap when liability insurance exists but the damages exceed the available liability limits, subject to the UM/UIM policy limit and the statutory framework.

First-party

Your insurer adjusts the claim

The insured must prove entitlement under the contract and statute, while the carrier retains the duties imposed on first-party insurers by Colorado law.

Colorado's statutory design is gap-filling. Section 10-4-609(1)(c) describes UM/UIM coverage as additional to liability coverage and ties available protection to damages sustained above legal-liability coverage, up to the UM/UIM coverage purchased.

Start with whether UM/UIM was purchased — or validly rejected

A Colorado automobile policy generally must provide the statutory UM protection unless the named insured rejects it in writing. The insurer also must offer the named insured the opportunity to obtain UM limits equal to the policy's bodily-injury liability limits, subject to § 10-4-609.

Colorado UM/UIM purchase and rejection framework.
Issue	Colorado rule	What to obtain
Basic UM/UIM coverage	Qualifying Colorado automobile liability policies must provide UM protection unless rejected in writing.	Declarations, full policy, endorsements and application/selection records.
Available limits	Before issue or renewal, insurer must offer the named insured the right to UM limits equal to bodily-injury liability limits.	Coverage-selection forms, quote history and policy declarations.
Written rejection	A named insured may reject the statutory UM protection in writing.	Actual signed/electronic rejection and proof of the policy period to which it applies.
2026 policy-summary protection	C.R.S. § 10-4-123 can make a written § 10-4-609 rejection voidable if a personal-auto insurer fails to comply with the statutory summary/language requirements.	Language-selection form, summary document, delivery record and rejection record.
Renewals	After selection or rejection, § 10-4-609 does not require repeated notice at every renewal, subject to other current statutory duties.	Prior selection/rejection plus any later written request or coverage change.

Do not accept “UM/UIM was rejected” without the file. Obtain the rejection itself, determine who made it and under what authority, identify the policy period, and test the rejection against the 2026 personal-auto summary requirements when they apply.

When does UM/UIM become relevant?

No liability insurance

Classic UM

The at-fault motorist lacks applicable liability coverage and the insured can establish covered liability and damages.

Insufficient liability insurance

Classic UIM

The at-fault motorist has liability insurance, but the insured's proved damages exceed the legal-liability coverage available.

Missing tortfeasor

Statutory uninsured status

Section 10-4-609(6) provides a mechanism under specified conditions for treating an unlocatable alleged tortfeasor as uninsured for UM-payment purposes.

Hit-and-run / phantom vehicle

Evidence becomes critical

Preserve scene evidence, witnesses, reports, video and prompt insurer notice. Missing-driver cases often turn first into evidence-preservation cases.

Multiple UM/UIM policies

Guide 05 problem

Separate policies, different insurers, resident-relative coverage and excess UM/UIM can create priority, stacking and exhaustion questions.

Rental vehicle

Special statutory exception

Section 10-4-609(1)(b) excludes motor-vehicle rental agreements and rental companies from subsection (1). Rental claims require separate contract and insurance analysis.

UM/UIM does not eliminate proof of the underlying crash. The insured ordinarily must establish the fault of the uninsured or underinsured motorist, causation, covered damages and the insured's own status under the policy.

Build the UM/UIM claim as a first-party proof file

The claim should show both sides of the gap: what the responsible motorist's liability coverage can provide and what covered damages remain after that layer.

1 Confirm insured status Named insured, resident-relative, occupant or other policy-defined insured status.

2 Confirm liability coverage Use Guide 03 to establish the tortfeasor's available liability limits and policies.

3 Prove fault Reports, witnesses, photographs, video, reconstruction and applicable traffic law.

4 Prove damages Medical, wage, future, noneconomic and other covered damages with admissible proof.

5 Preserve policy compliance Notice, cooperation, releases, settlement communications and policy-specific conditions.

Obtain the complete UM/UIM policy and all endorsements.
Obtain any rejection or limits-selection records.
For 2026 personal-auto policies, preserve § 10-4-123 summary/language records.
Document the at-fault motorist's liability coverage through Guide 03.
Identify every UM/UIM policy that may insure the injured person.
Separate undisputed covered benefits from genuinely disputed damages.
Respond to targeted insurer information requests in writing.
Track whether the carrier is investigating the claim as new information arrives.
Do not sign a tortfeasor release without reviewing UM/UIM policy conditions and subrogation issues.
Preserve admissible damages evidence rather than relying only on settlement evaluations.

Colorado does not permit an all-or-nothing approach to undisputed benefits

State Farm v. Fisher · 2018 CO 39

Pay what is undisputed

Fisher holds that an insurer may not unreasonably delay or deny an undisputed covered benefit merely because other components of the UIM claim remain reasonably disputed. The case involved covered medical expenses.

Colorado Supreme Court · controlling

Fear v. GEICO · 2024 CO 77

Not limited to medical bills

Fear extends Fisher's reasoning beyond medical expenses. Non-economic damages can be undisputed or not reasonably disputable in a particular case, but the insured still must prove the amount with admissible evidence.

Colorado Supreme Court · controlling

Evidence matters. Fear also holds that the type of internal settlement evaluation at issue there could not be used under CRE 408 to prove the amount of undisputed benefits, although such material may be admissible for another permitted purpose.

Wenzell changed the practical analysis of excess UIM exhaustion

Excess UIM coverage can sit above liability insurance and another UM/UIM layer. In 2026, the Colorado Supreme Court rejected the proposition that an excess carrier can simply wait for underlying carriers to physically pay their limits before its own adjustment duties arise.

Wenzell excess UIM exhaustion framework.
Issue	Wenzell rule	Practical consequence
Exhaustion clause	An excess UIM exhaustion clause can be valid.	Read the clause; do not assume all exhaustion provisions are void.
What constitutes exhaustion	Exhaustion turns on demonstrated undisputed damages exceeding all underlying policy limits.	Payment sequence by underlying carriers is not the controlling trigger.
Excess carrier duty	Once the required damages showing exists, the excess carrier must investigate, adjust, and address undisputed covered amounts above the underlying limits.	Send the damages proof to every implicated UM/UIM layer rather than waiting passively for lower carriers.

Wenzell follows the damages, not merely the checks. The insured still must demonstrate undisputed damages beyond all underlying limits. An excess carrier is not required to pay below the layer where its coverage attaches.

Cooperation is reciprocal with investigation — not a substitute for it

Colorado's first-party cooperation statute, C.R.S. § 10-3-1118, establishes procedures an insurer must follow before relying on a general failure-to-cooperate defense. Wenzell also makes clear that not every separately enumerated policy condition is the same thing as the general cooperation clause.

Written request

Specific information

For the statutory general-cooperation defense, the insurer's request must be written and seek information unavailable without the insured's assistance.

Reasonable need

Claim adjustment or fraud prevention

Section 10-3-1118 requires information a reasonable person would determine the insurer needs to adjust the claim or prevent fraud.

Response period

60 days

The statutory request must provide the insured sixty days to respond, followed by the required notice-and-cure procedure for an alleged failure.

Cure

Particularized notice

The insurer must describe the alleged failure and allow sixty days after receipt of the cure notice to remedy it before using the general defense.

Prejudice

Limited to affected claim portion

The statutory defense applies to the portion of the claim materially and substantially prejudiced to the extent the insurer could not evaluate or pay it.

Investigation

Carrier duty remains

The existence of a cooperation duty does not relieve the insurer of its own statutory duty to investigate and comply with Colorado claim-handling law.

Wenzell nuance: § 10-3-1118's procedural requirements govern the general failure-to-cooperate defense. Wenzell distinguishes that defense from a policy's separately stated conditions precedent. Read the actual policy before characterizing any request or defense.

UM litigation can put the insured's carrier into the underlying tort case

When the responsible motorist is uninsured, the insured may need to establish liability and damages while simultaneously pursuing first-party UM benefits. Colorado recognizes the tension created when the UM carrier seeks to participate in litigation against the uninsured motorist.

Progressive v. Ortiz, 2026 CO 40: reaffirming Brekke, the Colorado Supreme Court held that a UM insurer seeking an appropriate level of participation in tort litigation between its insured and an uninsured motorist must identify its legitimate defenses specifically and as soon as practicable. Boilerplate does not give the court the information needed to balance the insured's undiluted UM recovery against the carrier's right to a fair hearing on legitimate defenses.

Underlying tort

Liability must be established

UM benefits ordinarily depend on proving the uninsured driver's legal responsibility and the insured's damages.

Carrier defenses

Specific and timely

Ortiz requires legitimate defenses to be identified specifically and as soon as practicable when carrier participation in the tort case is at issue.

Bad-faith case

Different claim track

Contract benefits and unreasonable-delay/bad-faith issues can overlap factually but remain legally distinct questions requiring their own proof and defenses.

Colorado UM/UIM case authority map

Calderon v. American Family · 2016 CO 72

No MedPay setoff from UM/UIM payment

The Supreme Court construed § 10-4-609(1)(c)'s setoff prohibition as applying to the UM/UIM coverage actually available on the claim, not merely the abstract policy limit.

Colorado Supreme Court

State Farm v. Johnson · 2017 CO 68

Written rejection and agency

Colorado's UM/UIM statute does not displace ordinary agency principles. One named insured's rejection can bind other named insureds, and authorized agents may affect the rejection analysis.

Colorado Supreme Court

State Farm v. Fisher · 2018 CO 39

Undisputed covered benefits

A carrier cannot hold an undisputed covered benefit merely because other portions of the UIM claim remain reasonably disputed.

Colorado Supreme Court

Fear v. GEICO · 2024 CO 77

Non-economic damages can fall within Fisher

Non-economic damages are not categorically always disputed, but the insured must establish the undisputed amount with admissible evidence.

Colorado Supreme Court

USAA v. Wenzell · 2026 CO 25

Excess UIM and cooperation

Excess exhaustion is measured by demonstrated undisputed damages above underlying limits, and the opinion clarifies the scope of § 10-3-1118's general failure-to-cooperate procedures.

Colorado Supreme Court · rehearing denied May 11, 2026

Progressive v. Ortiz · 2026 CO 40

UM insurer participation in tort litigation

Reaffirms Brekke's requirement that a UM carrier identify legitimate defenses specifically and as soon as practicable when seeking participation in the underlying tort litigation.

Colorado Supreme Court

Primary authority map

C.R.S. § 10-4-609 UM/UIM statute

Offer, written rejection, limits, UIM inclusion, setoffs and unlocatable-tortfeasor provisions.

Official CRS portal →

C.R.S. § 10-4-123 2026 policy-summary protection

Personal-auto summary/language requirements and the voidability remedy for qualifying mandatory-coverage rejections.

Official CRS portal →

Regulation 5-2-16 · 3 CCR 702-5 Private-passenger policy disclosures

Implements the Colorado private-passenger automobile summary disclosure and Spanish summary-document system.

Colorado Code of Regulations →

C.R.S. §§ 10-3-1115 & 1116 Unreasonable delay or denial

First-party claim-handling duties and statutory remedies implicated by Fisher and Fear.

Official CRS portal →

C.R.S. § 10-3-1118 Failure-to-cooperate defense

Written-request, response, cure and prejudice requirements for the statutory general cooperation defense.

Official CRS portal →

Colorado Supreme Court Official opinions

Fisher, Fear, Wenzell, Ortiz, Calderon, Johnson and related current UM/UIM authority.

Official opinions →

2026 source control: the General Assembly's official 2026 CRS set is current through the changes made by the Seventy-fifth General Assembly at its Second Regular Session in 2026. Policy language and current primary authority control over this guide.

Existing VictimsGuide UM/UIM tools remain useful

The new Guide 04 becomes the normalized doctrinal hub. Existing Colorado resources can remain as supplemental educational and workflow tools during the transition.

Existing Guide to UM/UIM Legacy Colorado guide to mine, preserve and later redirect or relabel after normalization. Guide 03 — Find Every Policy Establish tortfeasor liability coverage and additional insurance before final UIM evaluation. Clean Claim System Chronology, damages proof, coverage map and first-party claim organization.

Frequently asked questions

Is UM/UIM automatically included in every Colorado auto policy?

Qualifying Colorado automobile liability policies generally must provide the protection described in C.R.S. § 10-4-609 unless the named insured rejects it in writing. The actual policy, selection/rejection documents and current 2026 summary-document rules should be reviewed.

What is the difference between UM and UIM?

UM addresses qualifying losses caused by an uninsured motorist. UIM addresses the gap when the responsible motorist has liability coverage but the insured's covered damages exceed that liability layer. Colorado includes UIM within its statutory uninsured-motorist protection.

Can a UM/UIM rejection from an earlier policy period still matter?

Yes. Section 10-4-609 addresses continuing selection/rejection treatment at renewal. But the actual rejection, later coverage changes and the 2026 personal-auto policy-summary requirements under § 10-4-123 must be examined before concluding that a rejection is valid for the loss.

Can an insurer subtract MedPay from what it owes under UM/UIM?

Colorado's § 10-4-609(1)(c) contains a broad setoff prohibition. In Calderon, the Colorado Supreme Court held that MedPay could not be set off from the UM/UIM amount actually available on that claim.

Does the UM/UIM carrier have to pay anything before the whole claim is settled?

Potentially yes. Fisher holds that an insurer may not unreasonably withhold an undisputed covered benefit merely because other parts of the UIM claim remain reasonably disputed. Fear confirms the principle is not categorically limited to medical expenses, though admissible proof of the amount remains necessary.

Can an excess UIM carrier wait until the primary UIM carrier pays its limits?

Not merely for that reason. Wenzell holds that a valid excess exhaustion clause is measured by demonstrated undisputed damages exceeding all underlying policy limits, rather than by the physical payment sequence of underlying insurers.

What if the insurer says I did not cooperate?

Section 10-3-1118 imposes specific procedures for a general failure-to-cooperate defense, including written requests, a 60-day response period, notice and an opportunity to cure. Wenzell also distinguishes that general defense from separately enumerated policy conditions precedent, so the actual policy must be read.

Does UM/UIM cover a hit-and-run?

Colorado authority recognizes UM protection in qualifying hit-and-run and unknown-motorist situations, and § 10-4-609(6) contains a specific mechanism for certain unlocatable alleged tortfeasors. Evidence preservation and prompt policy notice are especially important.

Can I settle with the at-fault insurer before finishing the UM/UIM claim?

A liability settlement can affect the UM/UIM file. Before signing a release, review the actual UM/UIM policy for notice, consent, cooperation, subrogation and other conditions; confirm every liability layer; and preserve the proof of damages and remaining UIM gap.

Does the rental car company's optional insurance have to include Colorado UM/UIM?

Section 10-4-609(1)(b) expressly excludes motor-vehicle rental agreements and rental companies from subsection (1), and Hertz v. Babayev, 2026 CO 26, reinforces the statutory distinction between rental companies and insurers. Guide 13 addresses rental-vehicle coverage separately.

UM/UIM file checklist

Complete declarations and policy with all UM/UIM endorsements.
Original UM/UIM offer, limits selection and any rejection.
2026 policy-summary/language-selection records when applicable.
Every policy that may provide liability coverage to the responsible motorist.
Every policy under which the injured person may qualify as a UM/UIM insured.
Crash report, photographs, witnesses, video and liability evidence.
Medical causation and admissible damages proof.
Chronology of all insurer requests, responses, evaluations and payments.
Written identification of undisputed versus disputed covered benefits.
Any cooperation demand, 60-day request, cure notice or asserted condition precedent.
Every proposed release, settlement agreement and subrogation-related communication.
For excess UIM, proof showing whether undisputed damages exceed all underlying limits.

Closing principle: UM/UIM should be treated as its own first-party claim, not as an afterthought to the liability settlement. Establish coverage, preserve policy conditions, prove the remaining damages gap, separate undisputed benefits, and make every implicated carrier adjust the layer it may owe.

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