A crash involving an uninsured or underinsured driver can turn into a second problem after the collision itself: an insurance fight over UM/UIM coverage. That fight often starts quietly, with a release signed too early, a deadline missed, or a statement given before the medical picture is clear.
UM/UIM claims are often misunderstood because they sit in an awkward middle ground. You may be making a claim under your own policy, but the dispute can still feel adversarial. Rules vary by state, policy wording matters, and the details that seem minor at first can affect timing, leverage, and the amount in dispute. The National Association of Insurance Commissioners explains that uninsured and underinsured motorist coverage exists to protect insured people when the at-fault driver has no insurance or not enough insurance to cover the loss, and its recent database report notes that state rules differ significantly on whether UM is required, offered, or waivable, and how UIM is structured. NAIC
If you want the broader foundation first, it may help to start with this overview of how uninsured and underinsured motorist coverage works in serious injury cases. In this post, the focus is narrower: seven common mistakes that can complicate recovery after an accident.
The stakes are real. According to the Insurance Research Council, about 14.0% of U.S. drivers were uninsured in 2022—roughly one in seven—and newer IRC reporting indicates the combined share of uninsured and underinsured motorists remained a major issue through 2023. Insurance Research Council, Insurance Research Council That helps explain why UM/UIM disputes show up so often after serious wrecks.
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One of the most common UM/UIM mistakes is assuming the claim can wait until the liability case is over.
Many people focus first on the at-fault driver’s insurer, which is understandable. But UM/UIM claims often involve separate notice obligations under the policy and, in some states, under statute. New York’s Department of Financial Services, discussing SUM coverage, states that written notice of claim is required “as soon as practicable.” New York Department of Financial Services Arizona’s statute is even more specific: a claimant generally has to give written notice of intent to pursue UM or UIM benefits within set time frames, and later may have to request arbitration or file suit within another statutory window. Arizona Legislature
Here’s what often happens in real life:
That does not mean every late-notice situation destroys a claim. State law varies widely. But delay can create a side dispute that did not have to exist.
In general terms, early notice tends to preserve options. An attorney might help identify whether the policy requires prompt notice, sworn proof of claim, medical authorizations, or arbitration-related steps. If you are also trying to understand the paperwork side of these disputes, it may help to read more about reviewing settlement demands, policy limits, and notice issues in a UM/UIM case.
This is one of the costliest mistakes in underinsured motorist claims.
When the at-fault driver’s insurer offers its policy limits, the offer can feel like progress. But in many states and under many policies, settling with that driver without first addressing your own UIM carrier’s rights can create a major problem. The issue usually involves subrogation—your carrier may claim it had a right to pursue the at-fault driver after paying UIM benefits.
Several state laws expressly build out this process. Tennessee law describes a notice-and-response procedure when the liability carrier offers to settle and the UM carrier has to decide whether it consents, waives subrogation, and agrees to arbitration. Tennessee Code § 56-7-1206 West Virginia likewise provides a written-notice framework when a tortfeasor’s liability insurer offers policy limits and the UIM carrier is asked to waive subrogation rights. West Virginia Legislature Nebraska has a similar structure, including a deadline tied to the UIM carrier’s response to tentative settlement notice. Nebraska Legislature