Cumulative trauma claims in California: date of injury, liable employers and deadlines

A cumulative trauma (CT) claim alleges an injury built up over time from repetitive physical or mental activity at work, rather than from one event. CT claims are a growing share of California's caseload, and they are almost always litigated. They also turn on dates more than most claims: the date of injury, the last day of injurious exposure and the date a termination notice was given. This guide sets out the statutes that control those dates. It is general information, not legal advice.

The California Workers' Compensation Institute reported in 2026 that CT claims rose from about 1 in 11 California claims in 2018 to about 1 in 6 in 2025. For applicant firms that means more cases where the result depends on employment history, exposure dates and medical opinions on causation over many years of records.

What makes an injury cumulative

Labor Code 3208.1 separates two kinds of injury:

• A specific injury comes from one incident or exposure.
• A cumulative injury comes from repetitive mentally or physically traumatic activities over a period of time, whose combined effect causes disability or a need for treatment.

The same worker can have both. Labor Code 5303 says there is only one cause of action for each injury, and a specific injury and a cumulative trauma can't be merged into one. A case where a client hurt a shoulder lifting a pallet after years of overhead work may involve a specific injury and a separate CT, each with its own date and its own evaluation.

The date of injury

For a CT, the date of injury isn't the first day of pain. Under Labor Code 5412, it is the date the employee first suffered disability from the cumulative injury and knew, or in the exercise of reasonable diligence should have known, that it was caused by present or prior employment.

Both parts matter, and each needs its own evidence. "Knew or should have known" often turns on when a doctor first told the client the condition was work-related. Write down the evidence for both, because the date drives the statute of limitations, the employers who are liable and, after a termination, whether the claim is allowed at all.

Which employers are liable

Under Labor Code 5500.5(a), liability for a CT is limited to the employers who employed the worker during the one year immediately before the date of injury under 5412 or the last date of injurious exposure, whichever comes first.

The applicant may choose to proceed against one or more of those employers, who are then jointly and severally liable, and they sort out contribution among themselves.

Deadlines and the 90-day presumption

Calendar the 90th day after the claim form is filed on every CT case. A late denial changes the case.

Post-termination claims

Many CT claims are filed after a layoff or firing, which is where Labor Code 3600(a)(10) applies. A claim filed after a notice of termination or layoff, for an injury before the notice, is barred unless one of four exceptions applies:

1. The employer had notice of the injury before the termination notice.
2. Medical records from before the notice show the injury.
3. The date of injury under Labor Code 5411 falls between the notice and the effective date of termination.
4. The date of injury under Labor Code 5412 is after the notice.

A notice not followed by termination within 60 days doesn't count. For CT claims the fourth exception often carries the case, which is why the 5412 date needs evidence behind it.

Psychiatric claims have their own rules in Labor Code 3208.3: actual events of employment must be the predominant cause of the injury compared with all causes combined, the worker generally needs six months of employment with the employer, and 3208.3(e) sets a separate post-termination rule. A good-faith personnel action defense also applies.

An intake checklist for CT claims

• Full employment history for at least the last several years, with dates and duties.
• Every employer and insurer in the last year of injurious exposure.
• Last day of exposure and the reason it ended.
• First lost time, first treatment and the first medical opinion linking the condition to work.
• Any termination or layoff notice: date given, effective date, and whether termination followed within 60 days.
• Records predating any termination notice that mention the condition.
• Prior claims, specific injuries and non-industrial conditions that may raise apportionment.
• Claim form filing date and the 90-day date.

Evidence that helps a CT claim

A CT case is built from history the client may not think matters. At intake and early in the case, collect:

• A job description in the client's own words: tasks, weights, repetitions, hours, shifts and changes over time.
• Payroll or personnel records showing the dates of each role and any modified duty.
• Witness names, such as coworkers who did the same work.
• Every treating record, including urgent care, chiropractic and primary care visits that mention the symptoms.
• The claim form and the date it was given to the employer.
• Any termination, layoff or discipline documents, with dates.

The medical-legal evaluator will be asked to address causation over years, and sometimes to separate a specific injury from the cumulative one. A clear, served record of the work history makes that opinion more useful. Our QME and AME guide covers what to serve and when.

How a firm can track this

CT files are heavy on records and dates. A chronology that puts every employer, exposure period, medical visit and notice on one timeline makes the 5412 and 3600(a)(10) questions much easier to answer, and the QME needs the same history.

In PlaintiffStack, each workers' comp case holds the employer, date of injury and body parts, and agents read searchable records and propose facts and dates with the page they came from, for a person to accept. Scanned records and faxes aren't read yet, which matters for older CT files.