How Does Apportionment Work in California Workers Comp?

What does Labor Code 4663 require?

Labor Code 4663 requires disability to be divided by causation, with a medical explanation for any non-work share.

The key idea is causation. The doctor must look at what caused the permanent disability, not just what caused the injury event. A worker may have age changes on imaging. That does not prove those changes caused disability.

A valid opinion should name the non-work cause. It should explain how that cause produces current limits. It should give a reasoned percentage. A report that says half is non-industrial because of degeneration may be too thin.

Permanent disability values belong in the standard table.

Who has the burden of proof?

The employer or insurer has the burden to prove apportionment with substantial medical evidence.

The worker does not have to prove a perfect past. The insurer is the side asking to reduce the award. It must support that reduction. The QME or AME report is usually the main battleground.

Labor Code 4664 also matters because it limits liability to the work-caused share. But it does not let the insurer use vague labels. The evidence must still show how much disability was caused by non-work factors.

What does a strong QME report include?

A strong report gives a clear history, compares records, explains symptoms before and after work injury, and states a reasoned percentage.

The doctor should discuss job duties, treatment history, prior injuries, imaging, exam findings, and work limits. The report should not treat every older worker as partly disabled before injury. It should ask what the worker could actually do before the claim.

If the report is weak, the worker can request a supplemental report. The doctor can be deposed. The judge can reject a conclusion that is not substantial evidence.

How do workers fight unfair apportionment?

Workers fight it by proving pre-injury function, correcting the medical history, and forcing the doctor to explain the percentage.

Useful proof includes attendance records, job reviews, coworker statements, wage records, lack of prior care, and proof of full duty before the injury. These facts can show that an old condition was not disabling.

The attorney can also send records to the QME, ask focused questions, and take a deposition. The goal is not to hide old facts. The goal is to make the split fair and based on real evidence.

What if the judge accepts the apportionment?

A worker may challenge an unsupported finding through reconsideration, but the record must be built before that point.

Appeals are not a place to add a brand new case. The stronger move is to build the record before trial. That means fixing the QME report, adding missing records, and making the legal issue clear.

If the final decision relies on a report that lacks substantial evidence, a Petition for Reconsideration may be available. Deadlines are short, so the decision should be reviewed at once.

What records should I gather now?

The best apportionment dispute record is built early, with job proof, medical proof, wage proof, and clear notes about what changed.

Start with the basics. Save prior medical records, old ratings, job duty proof, witness names, attendance records, performance reviews, and the full QME or AME report. Keep the papers in date order if you can. A simple folder on your phone can help. Take screenshots before messages disappear. Write names with job titles, not just first names.

Medical proof should be clear and practical. Keep every work status slip. Keep every report that lists restrictions. Keep visit summaries and referral notes. If a doctor writes something wrong, ask how to correct it. Small errors can grow into large disputes later.

Wage proof also matters. Save pay stubs, direct deposit records, tip records, time cards, mileage notes, and missed-work calendars. Benefit disputes often turn on dates and wages. A clean record makes the claim easier to explain.

Do not edit records or guess at facts. If you are unsure about a date, say so. A careful timeline is better than a perfect-sounding story that later proves wrong. The goal is to make the record honest, complete, and easy for a judge or doctor to follow.

What mistakes should I avoid?

Avoid rushed choices, vague medical histories, missing documents, and settlement talks before the key apportionment dispute facts are checked.

The largest mistake is accepting a percentage because it appears in a medical report. A percentage is only as strong as the reasoning behind it. The doctor must explain the how and why, not just name age or degeneration.

A second mistake is trying to hide older symptoms. That can damage trust. A better plan is to explain what symptoms existed, what work you could still do, and what changed after the new injury.

Another mistake is using legal words before the facts are clear. Plain facts win these disputes. What job did you do? What did the doctor restrict? What did the employer know? What changed after the injury? Those answers should come before argument.

Also avoid signing broad papers without review. A release, resignation, voucher clause, or settlement term can close rights you still need. Ask questions before signing. Keep a copy of every page you sign.

How can a lawyer help without making the case harder?

A lawyer can organize the proof, ask the right medical questions, and bring the apportionment dispute issue to the WCAB when the insurer will not fix it.

Good representation should make the claim clearer. It should not turn every issue into a fight. The first job is to sort the facts. The second job is to decide which dispute matters most. Some issues need a letter. Some need a QME question. Some need a hearing.

Yazdchi Law focuses on practical next steps. That may mean getting treatment moving, correcting a report, filing a petition, preparing for deposition, or checking whether settlement terms protect the worker. The plan should fit the injury, the job, and the worker goals.

The consultation is free. The worker should bring claim numbers, adjuster letters, medical reports, job offers, denial letters, and any settlement papers. Clear documents let the review move faster and help identify the first useful step.