Stacked vs unstacked uninsured motorist coverage

Stacking lets you combine the uninsured and underinsured motorist limits for each car you insure, so a household with three cars and $100,000 of UM per car could have up to $300,000 available for one injured person. Unstacked coverage caps you at the limit for a single vehicle. Stacking costs more, and it is available only in states that allow it; many states ban it or let insurers write it out of policies.

Stacking applies to uninsured and underinsured motorist coverage, which pays for your injuries when an at-fault driver has no insurance or too little. It does not apply to liability coverage, which protects other people.

How stacking works

There are two forms of stacking:

• Intra-policy stacking: adding the UM limits for several vehicles on the same policy.
• Inter-policy stacking: adding UM limits from different policies under which you are an insured, such as your own policy and a policy covering a car owned by a relative you live with.

State law and policy wording decide whether either form is allowed.

An example

Say you insure three cars on one policy, each with uninsured motorist limits of $100,000 per person, and an uninsured driver seriously injures you while you are driving one of them. Your damages total $260,000 (hypothetical figures).

The same logic applies to underinsured motorist coverage: stacked limits sit above whatever the at-fault driver's insurer pays, subject to your state's rules for calculating UIM.

Where stacking is allowed

There is no single national rule. According to the Insurance Information Institute, about half the states prohibit stacking, and among the states that allow some form of it, some let insurers include anti-stacking provisions if they are clearly stated. A few examples show how differently states handle it:

• Pennsylvania makes stacking the default. When more than one vehicle is insured, the UM/UIM limit applies separately to each vehicle and the limits are added together. A named insured can waive stacking only by signing a statutory rejection form, and the insurer must reduce the premium for anyone who waives (75 Pa.C.S. § 1738).
• Florida lets insurers offer a non-stacking option. If you accept it on a signed form, coverage on two or more vehicles is not added together, and the insurer's rates for the limited version must reflect a UM premium reduction of at least 20 percent (Fla. Stat. 627.727(8)).
• Kansas limits stacking by statute. Total UM/UIM limits available cannot exceed the highest limit of any single applicable policy, regardless of how many policies are involved (K.S.A. 40-284(d)).
• South Carolina ties optional limits to the vehicle involved. Coverage above the basic required limits is available only to the extent of the coverage on the vehicle involved in the accident (S.C. Code § 38-77-160).

Courts in many states have also ruled on stacking disputes, so the answer for your situation can depend on case law as well as statute. Your agent or the state car insurance requirements lookup is the place to start, and a licensed attorney is the place to finish if a serious claim turns on it.

What stacking costs

Stacked UM is priced higher than unstacked because the insurer could pay more on a single claim. How much more depends on the state, the insurer and the number of vehicles. In Pennsylvania and Florida the law itself builds in a lower price for giving up stacking. The only reliable way to know the difference is to ask your insurer for both prices on the same policy.

Who benefits most from stacking

Stacking is most valuable when several of these are true:

• You insure two or more vehicles. With one car there is nothing to stack within the policy.
• Your health insurance is thin, with a high deductible, or you have no disability coverage to replace lost income.
• You have household members who do not own cars, such as children, who are protected by your UM coverage as passengers or pedestrians.
• Your state has a high uninsured driver rate. See uninsured drivers by state.
• You cannot afford, or cannot buy, higher UM limits on each car. Stacking can be a way to reach a higher total.

It is less valuable if you already carry high UM limits per vehicle, have strong health and disability coverage, or insure only one car.

How to decide: a checklist

1. Find out whether your state allows stacking and whether your current policy is stacked. Look for "stacked" or "non-stacked" next to UM on your declarations page (how to read your car insurance declarations page).
2. Check whether you signed a waiver. In states like Pennsylvania, a waiver signed years ago may still be in effect.
3. Get prices for both options on your actual vehicles.
4. Compare the cost with simply raising UM limits. Raising each car's limit may give similar protection, and it helps even if you are hurt in a car you do not own.
5. Weigh your health and disability coverage.
6. Revisit when the number of cars changes. Adding or selling a car changes the math.

The How much car insurance do I need? can help you test UM limits against your other coverages.

Common misunderstandings

• Stacking does not raise your liability limits. It affects only UM and UIM, which protect you and your passengers.
• Stacking does not double-pay a loss. You still recover only your actual damages; stacking raises the ceiling.
• Unstacked does not mean uninsured. You still have the per-vehicle limit you chose.
• Your choice usually covers your household. In Pennsylvania's form, for example, the named insured's waiver applies to "myself and members of my household."

Key takeaways

• Stacking adds UM/UIM limits across vehicles or policies; unstacked caps you at one vehicle's limit.
• Pennsylvania makes stacking the default and requires a signed waiver to give it up; Florida offers a cheaper non-stacked option.
• Kansas and South Carolina are examples of states that limit stacking by statute.
• Stacking is most useful for multi-car households with thin health coverage.
• Compare stacked pricing with simply buying higher UM limits per car.