Stacked vs. Unstacked UM/UIM Coverage in Arizona

By the FigureMyTax Editorial Team · How we calculate

In Arizona, every vehicle on a multi-vehicle policy carries its own uninsured or underinsured motorist coverage, so the limits can be stacked unless the policy contains clear and unambiguous language that prohibits it.

What stacking means

Most auto policies list a UM/UIM limit for each insured vehicle. Stacking adds those limits together after one injury, so a $100,000 limit on three vehicles becomes $300,000. Unstacked coverage pays only one limit. It matters only when your damages are larger than what the at-fault driver's insurer paid and larger than a single limit.

Arizona starts from stacking

The Arizona Supreme Court held in Franklin v. CSAA General Insurance Co. (2023) that a single policy insuring multiple vehicles provides separate UIM coverage for each vehicle, and that insurers cannot avoid that with technical definitions or limitation-of-liability clauses. In July 2026 the Court wrote that stacking is permitted unless the insurer includes clear and unambiguous policy language expressly prohibiting it.

A worked Arizona example

Say your policy carries $100,000 of UIM on each of three vehicles, your damages are $250,000, and the at-fault driver's insurer paid its $25,000 limit. The unpaid damages are $225,000. With stacking, the ceiling is $300,000, so you could collect the whole $225,000. If the policy clearly bars stacking, you select one coverage and the most you can collect is $100,000. Try your own numbers in the Arizona UM/UIM stacking calculator.

UIM is not capped by liability limits

The Court also held in Franklin that A.R.S. 20-259.01(B) does not limit UIM coverage to the policy's bodily injury liability limits, so the UIM limit can be higher or lower than the liability limit you carry.

How an insurer can limit it

Subsection (H) says that when multiple policies or coverages purchased by one insured on different vehicles apply, the insurer may limit coverage so only one policy or coverage, selected by the insured, applies to any one accident. The Court has emphasized that insurers must put unambiguous language plainly disavowing stacking in the policy. Read what subsection (H) and the cases say for the legal detail, and how UM and UIM differ for when each applies.

This is general information, not legal advice, and the state comparisons above are illustrative, not an exhaustive survey. Confirm how Arizona's rules apply to your specific case with a licensed Arizona attorney.