The 90-Day Workers’ Comp Presumption in California: What Starts the Clock—and What It Does Not Prove

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California Labor Code section 5402 generally gives the employer 90 days after the employee files the claim form to reject liability. If the claim is not rejected within that period, the injury is presumed compensable. Evidence discovered after 90 days may be admitted to rebut the presumption only if it could not have been obtained with reasonable diligence during the 90-day period.

The clock is tied to the filed claim form

Notice of an injury and filing a claim form are related but distinct events. An email, incident report, or supervisor conversation may require the employer to provide a DWC-1 form, yet the statutory 90-day investigation period is generally measured from the filed claim form. Preserve proof of the date the completed form was delivered.

Create a receipt record, not just a mailing story

Keep a copy of every side of the DWC-1, the delivery email or portal confirmation, certified-mail record, hand-delivery acknowledgment, or other proof showing what the employer or claims administrator received and when. Record weekends and holidays, but do not rely on informal counting when a deadline is disputed.

If the employer supplied a partially completed form, retain that version as well as the employee’s completed copy. If the form was returned through a supervisor, identify the person and date. The strongest timeline shows the document itself and its route to the recipient.

Track the investigation and the denial

Save requests for statements, medical authorizations, examinations, wage records, and follow-up correspondence. Preserve the denial notice and envelope or electronic transmission. The date printed on a notice may not answer when or how it was communicated.

A timely denial and a reasonable investigation are related but different questions. Conversely, the end of 90 days does not erase disputes over the scope of injury, disability, treatment, or benefits. Identify exactly what the presumption addresses and what remains contested.

Late evidence has its own test

When the carrier relies on evidence obtained after the period, ask when the underlying facts became available, what investigative steps were taken, and why the evidence could not reasonably have been obtained earlier. The statute focuses on reasonable diligence, not merely the date a report was signed.

The worker should also respond promptly to legitimate investigative requests and document any inability to comply. A complete record lets the parties evaluate whether delay resulted from missing cooperation, ordinary investigation, or lack of diligence.

Calendar companion issues separately

During the investigation period, medical treatment duties and temporary-disability questions can arise under separate rules. The 90-day investigation period is not a blanket permission to ignore every benefit request. Keep a parallel log of treatment authorizations, work-status reports, wage loss, and benefit notices.

The practical file should contain the claim form, receipt proof, a day-by-day deadline calculation, all investigative activity, the denial or acceptance notice, and the evidence cited. That record is more useful than the shorthand statement that the carrier “missed 90 days.”

For broader claim guidance, review the firm’s California workers’ compensation practice and the primary-source Case Library.