How Do Insurance Companies Determine Fault in an Accident?

Last Updated on October 18, 2026

By James Shaffer Reviewed by Thomas Rockford, insurance industry executive and financial analyst, on October 18, 2026 How we fact-check

After a car accident, your insurance company (and the other driver’s insurer) will investigate what happened to decide who is at fault. That decision can impact how much money gets paid for vehicle repairs and injuries—and it can also affect what you pay for coverage at renewal.

Determining fault isn’t always simple. Crashes happen fast, drivers remember events differently, and the evidence doesn’t always point in one clear direction. Below is how insurers typically determine fault, what “no-fault” really means, and what you can do to protect yourself during the claims process.

Insurers determine fault by reviewing evidence like police reports, driver and witness statements, photos/video, vehicle damage patterns, and sometimes dashcam or vehicle data.
In most no-fault states, PIP pays injury claims through your own policy first, but fault still matters for vehicle damage and many larger claims.
Shared-fault decisions are common: insurers may assign percentages (like 80/20 or 50/50), which can reduce what you’re paid depending on your state’s negligence rules.
If you disagree with a fault decision, provide additional evidence, request a re-review, and consider escalating to your state insurance department or an attorney for high-dollar disputes.

Table Of Contents

Fault vs. No-Fault States
How Insurance Companies Determine Fault
What If Both Drivers Share Fault?
What Happens If You’re Found at Fault?
Quick Steps After a Crash That Help the Fault Investigation
FAQs on How Insurance Companies Determine Fault
Bottom Line
Sources

Fault vs. No-Fault States

Auto insurance rules are different in every state. But most states fall into one of two systems: at-fault (tort) or no-fault. The system affects how injury claims are handled and when you can sue, but fault still matters in most accidents—especially for vehicle damage.

At-Fault States

In most states, the person who caused the crash is financially responsible. This is often called an at-fault system or a tort system. If you’re found at fault, your liability insurance pays for the other person’s injuries and property damage (up to your limits), and the other driver may be able to sue depending on the situation.

No-Fault States

In no-fault states, injury claims typically go through your own policy first, regardless of who caused the crash. That’s why these states usually require personal injury protection (PIP), which helps pay for medical bills after an accident. No-fault rules can also affect whether insurance is more expensive in a no-fault state, depending on where you live and how your state structures benefits and lawsuits.

Important: Even in no-fault states, property damage is usually handled based on fault. No-fault is mainly about how injury claims are paid and when lawsuits are allowed. The Insurance Information Institute counts 12 no-fault states plus Puerto Rico, and in three of them, Kentucky, New Jersey and Pennsylvania, drivers can choose to reject the limits on lawsuits. Michigan adds a twist for car damage: for crashes after July 1, 2020, you can recover up to $3,000 of vehicle damage your insurance doesn’t cover from a driver who was more at fault, as long as you were not more than 50% at fault yourself.

If you want the deeper breakdown of how no-fault systems work (including lawsuit thresholds), start here: how no-fault auto insurance works.

How Insurance Companies Determine Fault

The people who do the investigating are typically insurance claims adjusters. Their job is to gather evidence, apply state laws and policy language, and decide how the claim should be paid (including whether fault is shared).

In most cases, insurers determine fault using a combination of evidence—then compare that evidence against traffic laws and common crash patterns.

Evidence Insurers Use	Why It Matters	How You Can Help
Police report	Provides an official summary, diagrams, citations, and third-party observations.	File one when appropriate, then learn how to file a police report after an accident and whether insurers check police reports.
Driver statements	Explains what each driver claims happened and what they observed (signals, speed, lane position, etc.).	Stick to facts. Avoid guessing or apologizing. This includes not admitting fault even if you think you were in the wrong.
Witness statements	Independent accounts can confirm lane changes, red lights, following distance, and more.	If possible, collect names/phone numbers and follow this guide on getting witness statements after a car accident.
Photos & video	Vehicle damage angles, debris patterns, signage, skid marks, and road conditions can support or contradict statements.	Take wide and close photos, and follow a checklist for documenting damage and gathering evidence.
Vehicle/tech data	Some claims use dashcam footage, intersection cameras, event data recorders, phone usage indicators, or app/telematics data (where available).	Save and back up any dashcam footage immediately and tell your adjuster what you have.

Adjusters also look at crash-specific details like the point of impact, turning vs. through-traffic right-of-way, rear-end crash patterns, lane-change evidence, and whether a citation was issued. A ticket doesn’t automatically equal fault, but it can be a factor.

Some states write these patterns down. Massachusetts regulations list 19 situations, such as rear-ending another car, turning left across another car’s path or running a red light, in which a driver is presumed more than 50% at fault when insurers decide whether an accident counts against that driver’s premium, unless the evidence shows otherwise. That list is for insurance at-fault decisions in Massachusetts. It does not decide a lawsuit, and most states have no such list.

What If Both Drivers Share Fault?

It’s common for insurers to decide that both parties are partially at fault. When that happens, insurers assign each driver a percentage of fault (for example, 80/20 or 50/50). Your payout can be reduced based on your share of responsibility.

How shared fault affects your claim depends heavily on your state’s rules. Generally, states fall into one of these categories:

Pure comparative negligence: You may be able to recover something even if you’re mostly at fault, but your payout is reduced by your percentage.
Modified comparative negligence (50% or 51% bar): You can recover only if you’re below the state’s cutoff.
Contributory negligence: In a few places, being even slightly at fault can bar recovery (rules and exceptions vary).

Because partial-fault claims can involve negotiation between insurers, it’s smart to keep tight documentation of vehicle repairs through your insurance company, understand whether you need medical payments coverage if you already have health insurance, and know how pain and suffering may (or may not) be handled depending on your state, injury severity, and the available liability limits.

If evidence is unclear, insurers may split fault, sometimes evenly, and adjust as more documentation comes in. When two insurers disagree, they may negotiate, re-open the analysis as new information comes in, or take the dispute to intercompany arbitration. Arbitration Forums, which calls itself the largest arbitration and subrogation service in the country, runs programs for auto physical damage and PIP disputes.

What Happens If You’re Found at Fault?

If you’re found at fault in an accident, your insurer generally pays the other party’s damages under your liability coverage—up to your policy limits. If your limits aren’t high enough, you can be personally responsible for the difference, and the other party may choose to sue (which can raise the question: do I have to hire a lawyer to defend me if I’m sued?).

Fault also drives your own premium. The NAIC’s consumer guide notes that in some states insurers can’t charge you more because of an accident that wasn’t your fault, which is one more reason to get the fault decision right.

If you disagree with the fault decision, you can contest it by providing additional evidence (photos, video, witness contacts, diagrams) and requesting a re-review. For more serious disputes or larger claims, it may be worth working with an auto insurance lawyer who can help you understand your options.

If you believe your claim is being handled unfairly, you can also contact your state’s insurance department. The National Association of Insurance Commissioners keeps a directory of every state’s department on its website.

Quick Steps After a Crash That Help the Fault Investigation

If you want the best chance at an accurate fault decision, your actions immediately after a crash matter. Use this as a practical checklist (when it’s safe to do so):

Move to safety, check for injuries, and call emergency services if needed.
Exchange information (names, contact info, policy numbers, plate numbers).
Take wide and close photos/video of all vehicles, the road, and any relevant signs or signals.
Get witness contact information if anyone saw the crash.
Notify your insurer promptly and follow the proper way to file an insurance claim after an accident.

FAQs on How Insurance Companies Determine Fault

Do police decide who is at fault, or does the insurance company?

Police reports can be very influential, but insurers still make their own coverage and fault decisions based on all available evidence. A citation or police opinion may support a fault finding, but it isn’t always the final word for insurance purposes.

Can I still get paid if I’m partially at fault?

Often, yes—depending on your state. Many states reduce your payout by your percentage of fault (comparative negligence). Some states limit or block recovery once you reach a certain fault threshold, and a few apply very strict rules.

How long does it take for insurance to determine fault?

It varies. Simple crashes with clear evidence may be decided quickly, while disputed accidents can take longer—especially if the insurers are waiting on a police report, witness statements, medical records, or additional documentation.

What evidence is most helpful for proving fault?

Clear photos of the scene and vehicle damage, dashcam footage, independent witness statements, and a detailed police report are often the most helpful. The sooner you preserve evidence after a crash, the better.

Does a no-fault state mean nobody is “at fault”?

No. “No-fault” usually means injury claims go through your own policy first (often via PIP) and lawsuits may be limited for minor injuries. Fault still matters for property damage and for many more serious claims.

What if the other driver’s insurance denies fault?

Denials happen when evidence is unclear or disputed. You can submit additional documentation, use your own collision coverage (if you have it) while insurers work it out, and ask your insurer about subrogation or arbitration processes that may apply between carriers.

Can I challenge an insurance fault decision?

Yes. Ask your insurer what evidence they relied on, provide any new documentation you have (photos, video, witness contacts), and request a re-review. For major injuries or large losses, getting legal advice may also be appropriate.

Bottom Line

Insurance companies determine fault by collecting evidence (police reports, statements, photos/video, and sometimes vehicle/tech data) and applying state laws and policy rules. In no-fault states, injuries often go through your own PIP coverage first—but fault still matters for vehicle damage and many larger claims.

If you think fault is being assigned incorrectly, don’t panic—ask your adjuster what evidence they relied on, provide any documentation you have, and escalate appropriately when the stakes are high.

My advice is to ask the adjuster for the fault decision in writing, with the percentage and the evidence behind it. If you think it’s wrong, send your photos, video and witness names in one email and ask for a second look before you agree to anything.

Sources

Checked October 18, 2026