# Stacking (UM and UIM coverage)

> Stacking means adding together uninsured or underinsured motorist limits from more than one vehicle or policy. When state law allows it and why it matters.

Canonical page: https://accidentclaimfacts.com/glossary/stacking/  
Last reviewed: October 29, 2026 by the Accident Claim Facts editorial team  
General information, not legal advice. Talk to a licensed attorney in your state.

## Quick answer

Stacking means adding together the uninsured motorist (UM) or underinsured motorist (UIM) limits from more than one vehicle or policy, to create a larger total for one claim. Whether you can stack depends on state law and the wording of your policy.

## In a car accident claim

Stacking matters when the at-fault driver has no insurance or too little, and your injuries are larger than one UM or UIM limit. If you insure several cars, or more than one policy covers you, stacking can raise the total available from your own coverage.

Pennsylvania is one example. There, the uninsured and underinsured motorist limits for each insured vehicle are added together unless the named insured signs a waiver. Other states handle stacking differently, and some policies limit it, so the declarations page and the policy wording matter.

The guides to [uninsured driver accidents](https://accidentclaimfacts.com/accidents/uninsured-driver-accidents/) and [hit-and-run accidents](https://accidentclaimfacts.com/accidents/hit-and-run-accidents/) explain how UM and UIM claims work, including when your own insurer becomes the one you claim against.

## Example

> **Example:** A driver insures two cars on one policy, each with the same UIM limit, and lives in a state that allows stacking. The at-fault driver's coverage is too small to cover the injuries. Because the policy stacks, the injured driver can claim up to the two UIM limits added together, instead of the limit for one car.

## Related terms

- [Uninsured motorist coverage](https://accidentclaimfacts.com/glossary/uninsured-motorist-coverage/)
- [Policy limits](https://accidentclaimfacts.com/glossary/policy-limits/)
- [Phantom vehicle](https://accidentclaimfacts.com/glossary/phantom-vehicle/)

## FAQ

### How do you know if your policy has stacking?

Check the declarations page and the UM/UIM section of the policy, and ask your insurer. In a state like Pennsylvania, any waiver form you signed when you bought the policy also matters.

### Can you give up stacking?

In some states, yes. In Pennsylvania, limits stack unless the named insured signs a waiver. Whether a waiver is allowed, and what it must look like, depends on the state.

## Sources

- [Insurance Information Institute, Facts + Statistics: Uninsured motorists](https://www.iii.org/fact-statistic/facts-statistics-uninsured-motorists) — what uninsured and underinsured motorist coverage pays
- [Pennsylvania General Assembly, 75 Pa.C.S. § 1738](https://www.legis.state.pa.us/WU01/LI/LI/CT/HTM/75/00.017.038.000..HTM), checked October 29, 2026