California’s expert witness disclosure rules, set out in Code of Civil Procedure sections 2034.210 through 2034.730, require every party in a civil case to exchange written information about their trial experts on a fixed pre-trial schedule once any party demands it. The exchange is mutual and simultaneous, it has strict deadlines tied to the trial date, and an unreasonable failure to comply lets the other side move to exclude your expert’s testimony at trial.
How the Process Starts
Nothing happens until a party serves a written demand for the exchange of expert witness information. No court permission is required. The demand must be served by the 10th day after the initial trial date is set, or 70 days before trial, whichever is closer to trial.1California Legislative Information. California Code CCP 2034.220 – Demand for Exchange of Expert Witness Information When the trial date is set well in advance, the 70-day deadline is usually the one that controls.
The demand itself names the date on which all parties will exchange their expert information. That exchange date is 50 days before trial, or 20 days after service of the demand, whichever is closer to trial.2California Legislative Information. California Code CCP 2034.230 Either side can move for an earlier or later date on a showing of good cause. The windows are deliberately tight so there is still time to depose the other side’s experts before discovery closes.
The exchange goes to the other parties, not to the court. Keep a proof of service. If a dispute later arises about who complied, that document is the evidence.
What You Must Disclose
The exchange has three possible components, depending on who your experts are and what the demand requested.
The Expert List
Every party produces a written list with the name and address of each person whose expert opinion the party expects to offer at trial. Retained experts and non-retained experts both appear on this list. Treating physicians, investigating engineers, and other witnesses who formed opinions through their involvement in the underlying events are non-retained experts; a party or party’s employee, or anyone hired specifically to form opinions for the litigation, is retained.3California Legislative Information. California Code CCP 2034.210 – Exchange of Expert Witness Information If you do not intend to call any experts, the exchange must say so.4California Legislative Information. California Code CCP 2034.260
The Expert Witness Declaration
Every retained expert must be accompanied by an expert witness declaration, signed by the attorney under penalty of perjury, containing five specific items:4California Legislative Information. California Code CCP 2034.260
- A brief narrative of the expert’s qualifications.
- A brief narrative of the general substance of the testimony the expert is expected to give at trial.
- A representation that the expert has agreed to testify.
- A representation that the expert is sufficiently familiar with the case to give a meaningful deposition about the specific opinions they plan to offer, including their basis.
- The expert’s hourly and daily fees for providing deposition testimony and for consulting with the retaining attorney.
The fourth item is where litigants get into trouble. The attorney is representing, under penalty of perjury, that the expert is already prepared to sit for a deposition on the identified opinions. Filing the declaration before the expert has actually worked through the case materials invites a damaging deposition or a challenge to the declaration itself. Non-retained experts need only appear on the list; no declaration is required for them.
Reports and Writings
If the demand asked for them, each party must also produce all discoverable reports and writings its retained experts prepared in the course of forming their opinions. These documents are produced at the same time and place as the list and declarations.5California Public Law. California Code CCP 2034.270 Drafts, written analyses, and opinion-related notes typically fall within this category. Failure to produce the writings when demanded is a separate ground for exclusion, even if the designation and declaration are otherwise perfect, so confirm with your expert early what written materials exist.
Adding or Correcting Experts After the Exchange
California provides three distinct mechanisms for changing your expert lineup after the initial exchange. They are not interchangeable, and each has its own trigger.
Supplemental Designation
Within 20 days after the initial exchange, any party may file a supplemental expert list adding experts to address subjects covered by the other side’s designated experts, as long as the supplementing party had not already retained an expert on that subject.6California Legislative Information. California Code CCP 2034.280 The supplemental list must include the required declaration and all discoverable reports and writings, and the supplementing party must make the new experts available for deposition immediately, even past the normal discovery cutoff. This is a narrow response to a surprise, not a chance to upgrade an expert you already had.
Motion to Augment or Amend
If you need to add a newly retained expert, or to amend a declaration because an existing expert’s expected testimony has shifted, the vehicle is a motion to augment or amend under CCP 2034.610.7California Legislative Information. California Code CCP 2034.610 Only parties who timely participated in the original exchange may bring the motion, and it must be filed early enough before the discovery cutoff to allow a deposition. A meet-and-confer declaration is required.
To grant the motion, the court must find that the opposing party will not be prejudiced and must consider the extent of reliance on the original list. It must also find either that reasonable diligence would not have identified the expert earlier, or that the omission was due to mistake or excusable neglect and the moving party acted promptly on discovery.8Justia. California Code CCP 2034.620 – Conditions for Granting Motion to Augment or Amend Even when granted, the court will usually require the expert to sit for an immediate deposition and may impose other conditions.
Motion for Late Submission
A party that missed the exchange deadline altogether may move under CCP 2034.710 for permission to submit expert information late.9California Legislative Information. California Code CCP 2034.710 The court must find all of the following: no prejudice to the opposing party on the merits; mistake, inadvertence, surprise, or excusable neglect as the cause; and prompt action by the moving party to seek leave and serve the information on discovery of the error.10California Legislative Information. California Code CCP 2034.720
If relief is granted, the expert must be made available for immediate deposition, and the court may allow the opposing side to designate additional experts, continue the trial, or recover costs. “Excusable neglect” is a real standard. A party that simply forgot the deadline will struggle; a party whose new counsel inherited the case and discovered the gap has a better case to make.
Expert Depositions and Fees
The party noticing the deposition pays the expert’s reasonable and customary hourly or daily fee. The clock starts at the noticed time (or the expert’s arrival if later) and runs until the expert is dismissed, whether or not any questions are actually asked.11California Legislative Information. California Code CCP 2034.430 A daily rate applies only when the expert attends for a full day or was required to hold the day open and cancel other commitments. If opposing counsel arrives late, that tardy attorney personally owes the expert’s fee for the delay, capped at the rate charged to the retaining party.
What Happens If You Miss a Step
CCP 2034.300 requires the trial court, on timely objection, to exclude the expert testimony of a party who unreasonably failed to comply with the exchange requirements. There are four independent grounds:12California Legislative Information. California Code CCP 2034.300
- Failing to list the expert in the designation.
- Failing to submit the required declaration for a retained expert.
- Failing to produce discoverable reports and writings when demanded.
- Failing to make the expert available for deposition.
Two features of this remedy shape how it plays out in practice. The statute speaks of an unreasonable failure, which gives the court room to weigh circumstances; a small, quickly corrected oversight is not treated like a deliberate refusal. And only a party that itself made full and timely compliance can invoke exclusion. If you missed your own deadlines, the other side’s noncompliance is not a weapon available to you.