Arizona has the 7th-highest uninsured driver rate in the United States. Roughly 12% of drivers on Phoenix-area roads carry no insurance, and another 15-20% carry only the state minimum ($25,000 / $50,000 per ARS 28-4009). If one of those drivers hits you, the at-fault driver’s policy will not come close to covering your damages. Arizona’s Uninsured Motorist (UM) and Underinsured Motorist (UIM) stacking law — ARS 20-259.01 — is the legal mechanism that protects you when their insurance falls short.
Most Arizona drivers don’t know their own policies can stack. Here is exactly how it works, and how to claim it.
What ARS 20-259.01 Actually Says
Arizona Revised Statutes section 20-259.01 governs uninsured and underinsured motorist coverage. The statute contains a critical concept: when an insured has multiple vehicles on a single policy or multiple policies in a household, the UM/UIM limits can “stack” under specific conditions.
Stacking Within a Single Policy (Inter-Policy)
If your policy covers three vehicles at $50,000 UM coverage each, the law presumes those limits stack to $150,000 unless the policy contains a specific anti-stacking clause AND the carrier obtained your written waiver of stacking under ARS 20-259.01(D).
Stacking Across Multiple Policies (Intra-Household)
If you live in a household with multiple policies (yours, your spouse’s, an adult child on a separate policy), Arizona law has historically allowed claiming UM/UIM from any policy under which you qualify as an insured. This is where adjusters work hardest to limit you.
The Stacking Argument Adjusters Use Against You
When you file an UM/UIM claim, your own insurance company is now in an adversarial position with you. They will:
- Point to anti-stacking language in your policy
- Argue that any prior waiver you signed was binding
- Apply per-accident vs per-person limits in confusing ways
- Require “exhaustion” of the at-fault driver’s policy before paying UIM
- Dispute whether your injuries exceed the at-fault driver’s coverage
Your own carrier may be friendly when you pay premiums. They become adversaries when you claim. Treat the UM/UIM claim as a separate negotiation.
How to Calculate Your Available Stacked Coverage
- List every auto policy in your household. Yours, your spouse’s, any policy covering vehicles you don’t own but use regularly.
- Pull the declarations page for each. Identify the UM and UIM limits.
- Check each policy for anti-stacking language. Search for “non-stacking,” “reduction,” or “limit of liability” clauses.
- Look for stacking waivers. When you purchased the policy, did you sign a waiver of stacking? If you can’t find one, the law presumes stacking applies (ARS 20-259.01(D) places the burden on the insurer to prove a knowing waiver).
- Calculate total available coverage. Sum the applicable limits across stacked policies.
- Then look at the at-fault driver’s coverage. If their policy paid out fully and your damages exceed it, the gap is what UIM owes.
Hit by an uninsured or underinsured driver in Arizona?
Wood Injury Law stacks every available policy under ARS 20-259.01. $15M+ recovered for AZ clients. National Top 100 Trial Lawyers.
UIM vs UM — The Critical Distinction
Uninsured Motorist (UM) applies when the at-fault driver has no insurance at all. You file directly with your own UM carrier. No exhaustion requirement, no waiting.
Underinsured Motorist (UIM) applies when the at-fault driver has insurance but the limits are insufficient for your damages. Critical: most Arizona UIM policies have a setoff provision — your UIM only pays the difference between the at-fault driver’s coverage and your UIM limit, not the full UIM limit on top of the at-fault coverage.
Example: at-fault driver has $25,000. Your UIM is $100,000. Setoff: UIM pays $75,000. If the policy has “true excess” language (rare in Arizona), UIM would pay the full $100,000 on top. Read your policy.
Frequently Asked Questions
What is the statute of limitations for an UM/UIM claim in Arizona?
Two years from the date of the crash under ARS 12-542 for tort-based UM. Contract-based UIM claims may have a longer limitations period (6 years under ARS 12-548 for written contracts). But you must give your carrier prompt notice or risk a denial. Notify within 30 days of identifying the need.
If I waived stacking when I bought my policy, can I still stack?
Only if the waiver was “knowing” under ARS 20-259.01(D). The insurer must show you were informed of the right to stack and knowingly waived it. Generic policy language buried in fine print may not satisfy the knowing waiver requirement. This is litigated regularly.
Does my UM coverage apply if I was hit as a pedestrian or on a motorcycle?
Often yes. UM/UIM coverage typically attaches to the named insured (you) and resident family members, regardless of whether you were in a vehicle at the time. Read your “persons insured” clause.
What if the at-fault driver fled the scene? Does UM apply?
Yes. ARS 20-259.01 covers “phantom vehicle” or hit-and-run scenarios as long as you can establish the unidentified vehicle caused the crash. Documentation requirements vary by carrier; the police report and physical evidence are central.
Can my insurer raise my rates after a UM/UIM claim?
By Arizona statute (ARS 20-263.B), surcharges for not-at-fault claims are restricted. However, carriers sometimes apply “general experience” rate adjustments. If your rates are raised after a UM/UIM claim where you were not at fault, push back — your carrier may be in violation.
Don’t Leave Stacked Coverage on the Table
Wood Injury Law stacks every applicable policy under ARS 20-259.01 for Arizona UM/UIM claims. Josh Wood is a former insurance defense attorney — he wrote the same anti-stacking arguments the carriers are now using against you.
$15M+ recovered for clients. National Top 100 Trial Lawyers. 4.9 stars from 191 reviews. No fee unless we win.
