This coverage is commonly referred to as UIM coverage. This coverage will apply if another driver, who is legally responsible for an accident which injures you, is required to pay more than their bodily injury liability coverage limits. This coverage will pay up to the coverage limit, but only after all of the liable person's coverage limits have been exhausted. This coverage also protects relatives who live with you, and as a pedestrian.

The coverages and limits vary by state:

• Arkansas allows underinsured motorist coverage if uninsured motorist coverage has been purchased. Underinsured motorist coverage can be purchased at the same limit as uninsured motorist. If not desired, underinsured motorist coverage must be rejected in writing.
• Illinois underinsured motorist coverage is mandatory if uninsured motorist coverage has been purchased.  Underinsured motorist coverage must be purchased at the same limit as uninsured motorist coverage.  The minimum limit that can be selected is $25,000 per person and $50,000 per accident.  Higher coverage limits are available. 
• Indiana underinsured motorist coverage has the same limits as underinsured motorist coverage.  In order to purchase underinsured motorist coverage, you must also have uninsured motorist coverage of at least $50,000 per person and $100,000 per accident.  If not desired, this coverage must be rejected in writing.
• Kansas requires underinsured motorist coverage of $25,000 per person and $50,000 per accident. The limit purchased must be the same as the bodily injury liability limits unless waived in writing which allows lower limits.
• Louisiana refers to this coverage as UMBI, which is included in uninsured motorist coverage.
• Mississippi includes underinsured motorist coverage in the uninsured motorist coverage.
• In Missouri, underinsured motorist coverage is not required, but may be purchased at the same limits as uninsured motorist coverage (UM).
• Oklahoma includes underinsured motorist coverage in the uninsured motorist coverage.

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