Uninsured and Underinsured Motorist Coverage in Arizona

What Is Uninsured and Underinsured Motorist Coverage in Arizona?

Uninsured motorist (UM) coverage pays for your injuries when the driver who hit you has no insurance or flees the scene. Underinsured motorist (UIM) coverage pays when the at-fault driver has insurance, but not enough to cover your losses.

Both come from your own auto policy, and in Arizona, you probably have them.

Under A.R.S. § 20-259.01, every insurer has to offer UM and UIM coverage, and you only go without it if you rejected it in writing.

That coverage matters here more than in most states, because Arizona's minimum liability limits are low and a serious crash blows past them fast.

There is a catch most people do not expect: a UM or UIM claim is filed against your own insurance company, and the moment you do, it starts acting like the other side.

Knowing what coverage you have and how to make your own carrier pay it is where these claims are won.

UM vs. UIM: What Each One Covers

The two coverages solve two different problems, and a serious crash often triggers one or the other.

Uninsured motorist (UM). This applies when the driver who caused the crash carried no insurance at all, or when a hit-and-run driver is never identified. Arizona has a significant share of uninsured drivers on the road, so this is not a rare situation. Without UM coverage, an uninsured at-fault driver often means no one to collect from. With it, your own policy stands in for the coverage the other driver should have had.

Underinsured motorist (UIM). This applies when the at-fault driver has insurance, but the limits are too low to cover your injuries. On a catastrophic injury, an at-fault driver carrying Arizona's minimum can be exhausted by a single hospital stay. UIM coverage fills the gap between what the at-fault driver's policy pays and what your losses actually are, up to your UIM limit.

If you are not sure the at-fault driver's coverage is enough, see our breakdown of whether Arizona's minimum insurance is enough after a serious crash.

You Probably Have This Coverage, Even If You Forgot

People often assume they do not have UM or UIM coverage because they do not remember buying it. Arizona law works the other way.

A.R.S. § 20-259.01 requires every insurer writing auto policies in the state to make UM and UIM coverage available and to offer it to the named insured in writing.^[1] The coverage is part of the package unless you affirmatively rejected it, or selected lower limits, in writing. The limits can be set up to your liability coverage limits.

What this means in practice: after a crash with an uninsured or underinsured driver, the first thing to do is pull your own policy and check the declarations page. Many people discover UM and UIM coverage they did not realize they were paying for. An insurer that has the coverage on the policy cannot pretend it is not there, and a lawyer reading the policy closely is often how the coverage gets found and used.

When Your Own Insurer Becomes Your Opponent

A liability claim is filed against the other driver's insurer. A UM or UIM claim is different. It is a first-party claim, filed against your own insurance company, the one you have paid premiums to for years.

The relationship changes the moment you make the claim. Your carrier now has a financial reason to value your injuries low, dispute your treatment, and delay. The friendly company from the commercials becomes the adverse party at the table.

Arizona law does require your insurer to handle your claim in good faith. When it lowballs, stalls, or denies a valid UM/UIM claim without a reasonable basis, that conduct can itself become an insurance bad faith claim on top of the underlying coverage. Knowing the carrier is now an opponent, and being ready for it, is half the battle in a first-party case.

A lot of clients are surprised to find their own insurer not treating them fairly, because they still think of it as their company. The day you file a UM claim, it stops being that. Your own insurance company becomes the one standing between you and compensation in a UM claim. Your own insurance company must be treated like an adversary in order to force a fair evaluation of your injuries and losses.

Can You Stack UM/UIM Coverage in Arizona?

Stacking means combining UM or UIM limits, either across multiple vehicles on one policy or across more than one policy, to increase the total coverage available for a single crash. In the right circumstances, it can multiply what you recover.

Whether you can stack in Arizona depends on the policy language and the facts. A.R.S. § 20-259.01 lets an insurer require that the vehicles on a single policy carry the same UM/UIM limits, and policies often contain anti-stacking provisions. Those provisions are not always enforceable, and the analysis turns on how the policy is written and how many policies and vehicles are in play.

This is detailed, policy-specific work, and it is easy to leave coverage on the table by assuming a single limit is all that applies. Reviewing every policy in the household is part of finding the full coverage available to a serious claim.

UM vs. UIM Coverage in Arizona at a Glance

The two coverages solve two different problems, but both come from your own policy and both must be offered under Arizona law:

How It Works	Uninsured Motorist (UM)	Underinsured Motorist (UIM)
When it applies	The at-fault driver has no insurance, or fled the scene	The at-fault driver has insurance, but not enough
What it pays	Stands in for the coverage the other driver should have had	Fills the gap above the at-fault driver's limits
Whose policy pays	Your own	Your own
Must insurers offer it	Yes, under A.R.S. § 20-259.01	Yes, under A.R.S. § 20-259.01

Because both are first-party coverages, the carrier handling the claim is your own. Knowing which one applies, and whether more than one policy is in play, is where these claims are won.