Proving Fault in Personal Injury Accidents: General Rules

How to decide who is legally at fault for an accident or personal injury.

Updated by , Attorney · University of Missouri–Kansas City School of Law

Determining legal responsibility for an accident or injury (called "liability") can be complicated, but often rests on whether someone acted carelessly. It's easy enough to say that the person or business that caused an accident must pay for your injuries. But before you get to that point, you have to determine who was legally at fault.

We'll take you through the basic rules for determining who's at-fault in an accident, who pays when more than one person is to blame, how your fault can reduce the value of your claim, and more.

Determining Legal Liability

Most accidents happen because someone was careless, or as the law calls it, "negligent." The basic rule is: If one person involved in an accident was less careful than another, the less careful one must pay for at least a portion of the damages suffered by the more careful one.

Legal liability for almost all accidents is determined by the rules of negligence (carelessness), and by one or more of the following rules.

Trespassing and Assumption of the Risk

If the injured person was where they weren't supposed to be (for example, they were trespassing), or somewhere they should have expected the kind of activity which caused the accident (the law calls this "assumption of the risk"), the person who caused the accident might not be liable.

Why? Because in those situations, the person who caused the accident probably had no legal "duty" to be careful toward the injured person.

Comparative Negligence

If the injured person was also careless, in most states their compensation will be reduced by the percentage of their own fault for the accident. We'll explain this comparative negligence rule in more detail below.

Employer Liability for Employee Negligence

If a negligent person causes an accident while working for someone else, their employer might also be legally responsible for the accident. The fancy legal name for this rule is "respondeat superior," meaning "let the superior answer."

Dangerous Conditions on Property

If an accident happens on a property that is dangerous because it is poorly built or maintained, the owner of the property can be liable for being careless in maintaining the property, even if the owner didn't actually create the dangerous condition.

For example, a property owner can be responsible for a fall on an icy parking lot if the owner carelessly failed to remove the ice. The owner didn't cause the ice to be there, but negligently failed to get rid of it.

Liability for Defective Products

If an accident is caused by a defective product, both the manufacturer and seller of the product can be legally liable for injuries it causes. This can be true even if the injured person doesn't know which one was careless in creating or allowing the defect, or exactly how the defect happened. The law calls this a "product liability claim."

When More Than One Person Is at Fault

When more than one person is responsible for an accident—for example, if several careless drivers cause a wreck—the law in most states says that you can collect compensation for your injuries from any one (or more) of the careless parties you choose. This rule is called "joint and several liability."

The joint and several liability rule has a couple of important advantages. First, if one liable person is insured and the other is not, you can make your claim against the insured person for the full amount of your damages. Collecting from the uninsured person isn't your problem. The responsible parties decide among themselves whether they have to reimburse each other.

Second, even if all the liable persons are insured, you only have to settle your claim with one insurance company. When you first make your injury claim, notify everyone you think might be liable that you plan to file a claim.

Then, as you learn more about how the accident happened, you can pursue your claim against one liable person and that person's insurance company and collect all your compensation. Let the insurers fight each other over reimbursement.

How Your Own Fault Affects Your Claim

We mentioned the comparative negligence rule above. Here's a bit more about how it works.

In most states, even if you partly cause an accident, you can still get some compensation from anyone else who was also partly responsible. The amount of the other person's liability for the accident is determined by comparing their carelessness with your own. The other person's percentage of liability determines the amount of the resulting damages they must pay.


Bob was driving a bit too fast in a school zone. Out of the corner of his eye, he spotted a child on the sidewalk and thought the child was about to dart out into the road. Instinctively, Bob slammed on his brakes, stopping suddenly. Bob's car was hit from behind and Bob suffered personal injuries. If the other driver had been 100% at fault, Bob's medical bills and lost income would entitle him to $5,000.

The insurance company for the driver whose car hit Bob points out that Bob should have been going slowly enough in the school zone to be able to stop without having to slam on his brakes.

Let's assume that Bob was 10% negligent and the other driver was 90% negligent. Because of Bob's comparative negligence, the person who hit him isn't liable to Bob for the full compensation of $5,000. Instead, Bob is entitled to collect $4,500 ($5,000 x 90% = $4,500).

There is no easy-to-apply rule or formula for figuring out each person's share of the blame. You and an insurance adjuster will discuss all the factors that might have caused the accident. Your comparative negligence gets negotiated along with all the other factors that determine the value of your claim—like the seriousness of your injury and the amount of your medical bills.

(Learn more about how an insurance company calculates the value of your case.)

Different Comparative Negligence Rules

There are three different kinds of comparative negligence rules: Pure comparative negligence, modified comparative negligence, and contributory negligence. The rule in your case depends on the state where the accident happened.

Pure Comparative Negligence

The more generous states allow you to recover compensation for your injuries no matter how big your share of the fault, as long as it's less than 100%. Even if you're 99% to blame and the other party is 1% to blame, you can collect 1% of your total damages.

Modified Comparative Negligence

Most states use a less generous comparative negligence rule. In these modified comparative negligence states, you can't recover anything if you were 50% or more to blame (in some states, it's 51% or more) for the accident.

Contributory Negligence

A handful of tight-fisted states don't allow you to recover any compensation at all if your fault contributed in any way to the accident. This is called "contributory negligence," and it's a harsh rule. If you're even 1% to blame for an accident, you're not allowed to collect any damages.

Next Steps

If you've been in an accident and think you might have a personal injury claim, the legal rules can be a bit overwhelming. We've covered some of the basics here, but even they can be tricky to apply if the facts or legal issues in your case are complicated.

If you need help understanding how these or other legal rules apply to your case, give some thought to consulting with an experienced personal injury lawyer in your area. A seasoned attorney who regularly handles cases like yours can guide you through the process and help you get the best possible outcome. Here's how to find a personal injury lawyer who's right for you and your case.

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