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✦ Certified Specialist in Workers’ Compensation Law — Certified by the State Bar of California, Board of Legal Specialization ✦
Serving injured workers across California. Board-certified specialist; no fee unless we win.
By Eman Yazdchi, Esq. · Certified Specialist in Workers' Compensation Law, State Bar of California Board of Legal Specialization
In California, Labor Code §4663 lets a workers' compensation insurer apportion permanent disability between industrial causes and non-industrial causes — directly reducing the PD award. The burden of proving apportionment rests on the employer. Yazdchi Law handles California §4663 apportionment disputes statewide.
California Labor Code §4663 allows a California workers' compensation insurer to apportion the injured worker's permanent disability between industrial causes (the work injury) and non-industrial causes (pre-existing conditions, prior injuries, degenerative changes, recreational activities). The §4663 California rule directly reduces the California Labor Code §4660 permanent disability award by the percentage attributed to non-industrial causes. The §4663 burden of proving California apportionment rests squarely on the employer or insurer, not the injured worker.
Under California Labor Code §4663, if a California medical evaluator assigns 40% of a worker's lumbar disability to pre-existing degenerative disc disease and 60% to the industrial injury, the California Labor Code §4660 permanent disability award is reduced by 40%. The §4663 California reduction applies dollar-for-dollar to the PD payment schedule under California Labor Code §4658. A California worker who would otherwise receive a $100,000 PD award with 40% non-industrial §4663 apportionment receives $60,000 instead.
Under California Labor Code §4663, the California burden of proving apportionment rests on the employer or insurer — not the injured worker. The §4663 California employer must produce substantial medical evidence from a treating physician, Panel Qualified Medical Evaluator under California Labor Code §4062.2, or Agreed Medical Evaluator that identifies a specific non-industrial cause and quantifies its contribution to the worker's permanent disability. An asymptomatic pre-existing California condition is a weak basis for §4663 apportionment; symptomatic prior injuries with prior PD awards are the strongest basis.
Under California Labor Code §4663, California apportionment must be supported by substantial medical evidence — meaning the medical evaluator's opinion must identify the specific non-industrial cause, quantify its percentage contribution, and explain the reasoning under the AMA Guides 5th Edition framework that California Labor Code §4660 incorporates. Conclusory California §4663 apportionment opinions — "I think 50% is non-industrial" — without underlying analysis are routinely rejected by California WCAB judges as not substantial evidence.
Under California Labor Code §4663 (general apportionment) and California Labor Code Section 4664 (prior-PD apportionment), California has two related apportionment frameworks. The §4663 California rule covers apportionment to any non-industrial cause. Section 4664 covers apportionment to prior permanent disability — when the worker has a prior California PD award for the same body region, that prior PD is conclusively attributable to the prior injury and is subtracted from the current rating. The §4663 California rule does most of the apportionment work; Section 4664 handles the prior-PD-overlap cases.
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Tap to call →Last reviewed by Eman Yazdchi, Esq., May 2026.
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