Auto Insurance

Stacking (UM/UIM)

Combining UM/UIM limits across multiple vehicles or policies to increase the total protection available.

Last reviewed: May 2026 · Editorial methodology

Definition

Stacking allows you to add together the uninsured/underinsured motorist (UM/UIM) limits from multiple vehicles or policies to create a larger coverage pool. For example, if you own three vehicles each with $100,000 in UM coverage, stacked coverage provides up to $300,000 per accident. Interstate stacking — combining policies from multiple insurers — is less common and more complex than intra-policy stacking. About half of U.S. states permit stacking; others prohibit it or allow insurers to include anti-stacking language. Florida and Pennsylvania explicitly allow it, while California generally does not. Stacked coverage costs more but significantly improves protection in serious accidents.

Where this term matters

Auto Insurance →

Tip

Glossary definitions are educational. Always check your own policy language — insurers can define common terms differently from one another. When in doubt, request a written explanation from your agent.

Related terms

Uninsured/Underinsured Motorist (UM/UIM)Auto coverage that pays your injuries and damage when the at-fault driver has no/inadequate insurance.Bodily Injury Liability (BI)Auto liability coverage that pays for injuries you cause to other people in an at-fault accident.PIP (Personal Injury Protection)Auto coverage that pays your medical bills and lost wages after an accident regardless of fault.No-Fault InsuranceAn auto insurance system where each driver's own insurance pays their injuries regardless of fault.

Related guides

Source: Cover Forge USA editorial team|Last verified: May 2026|Methodology
Definitions are educational and may be simplified. Always refer to your policy contract and consult a licensed agent for terms that affect coverage decisions.
CF

Cover Forge USA Editorial Team

Editorial Lead

This article was researched and written by the Cover Forge USA editorial team against federal sources (NAIC, CMS, FEMA, DOL, SSA, state DOIs) and standard policy forms. Bylines organize content by topic — they do not assert individual licensure. See our editorial-policy for details.

Reviewed June 2026

Get Insurance Updates

Occasional updates on insurance rules, coverage changes and new guides — and ways to save.

  • ✓State-specific insurance rule changes
  • ✓Seasonal enrollment deadline reminders
  • ✓Expert tips to lower your premiums
  • ✓New coverage options in your state

Free forever. Unsubscribe with one click. No spam, ever.

Important Disclaimer

This site provides general educational information only and is not a substitute for professional insurance advice. All rates, data, and coverage details are estimates and may not reflect your actual premiums. Insurance availability and pricing vary by state, insurer, and individual risk factors. Always consult a licensed insurance professional in your state before making coverage decisions.

← Back to Insurance Glossary (355 terms)