Underinsured/Uninsured Motorists Stacking Provisions

Underinsured motorist coverage, sometimes abbreviated UIM, and uninsured motorist coverage, sometimes abbreviated UM, are included in motor vehicle insurance policies as a consequence of the fact that many owners and operators of cars and trucks either do not maintain adequate insurance coverage on their vehicles or operate those vehicles without any insurance coverage at all. Underinsured motorist and uninsured motorist provisions in auto insurance policies attempt to provide persons insured under a policy and innocent third parties with some of the insurance protection they would have had if an underinsured or uninsured motorist with whom they are involved in an accident had maintained the appropriate insurance coverage on his or her vehicle.

The process called "stacking" of uninsured or underinsured motorist coverage occurs when a person making a claim under an auto insurance policy attempts to recover more than the amount of coverage specified by the policy for the particular loss that has been suffered. This may happen because the uninsured motorist or underinsured motorist coverage in a policy does not provide a sufficient amount to fully indemnify the claimant for the damages that have been suffered. Stacking claims are often made where a policy covers more than one vehicle or where more than one policy is involved, so that the claimant can argue that separate uninsured motorist or underinsured motorist limits for each such vehicle or policy, rather than a single such limit, should apply, thus allowing a greater recovery than would otherwise be available. Insurers often include provisions in their policies that attempt to prohibit or restrict the use of stacking, and state insurance statutes often contain provisions on the subject of stacking.

The business of insurance, including motor vehicle insurance, has traditionally been regulated by the law of each state rather than by a single unified system of federal law. As a result, the answers to questions related to stacking of uninsured motorist or underinsured motorist coverage may vary widely from one state to another.