Expert Witness Disclosure in California: The Demand, the Exchange, and What Happens if You Miss It

Last updated: November 2026. Reviewed by Pavel Kolmogorov, California business litigation attorney (State Bar No. 321018).

Expert witness disclosure is the exchange, late in a California case, of each side's list of experts it expects to call at trial. Any party may demand it once the first trial date is set. The exchange takes place 50 days before that trial date, or 20 days after the demand is served, whichever is closer to trial. A party that unreasonably fails to disclose an expert can have the expert's opinion excluded. (Code Civ. Proc., §§ 2034.230, 2034.300.) Kolmogorov Law, P.C. represents companies and their owners in business disputes.

Call (909) 235-6116 or contact us online to discuss a business case that is approaching trial.

The demand and its timing

There is no exchange unless someone asks for one. After the initial trial date is set, any party may demand that all parties simultaneously exchange information about their expert trial witnesses. (Code Civ. Proc., § 2034.210.) No court permission is needed. The demand must be made no later than the 10th day after the initial trial date has been set, or 70 days before that trial date, whichever is closer to the trial date. (Code Civ. Proc., § 2034.220.)

The demand is in writing and names the date of the exchange. That date is 50 days before the initial trial date, or 20 days after service of the demand, whichever is closer to the trial date. The court may order a different date on motion and a showing of good cause. (Code Civ. Proc., § 2034.230.) Our litigation deadlines guide places these dates alongside the other pretrial deadlines.

What each side must exchange

On or before the exchange date, every party that has appeared must provide one of two things in writing. The first is a list with the name and address of each person whose expert opinion it expects to offer at trial. The second is a statement that it does not presently intend to offer expert testimony. (Code Civ. Proc., § 2034.260, subds. (a), (b).)

If the expert was retained to form and express an opinion for the litigation, or is a party or an employee of a party, the list must come with an expert witness declaration. (Code Civ. Proc., § 2034.210, subd. (b).) A chief financial officer or an engineer on the payroll who will give opinion testimony must be disclosed this way.

The attorney signs the declaration under penalty of perjury. It must contain:

A brief narrative statement of the expert's qualifications.
A brief narrative statement of the general substance of the expected testimony.
A representation that the expert has agreed to testify at trial.
A representation that the expert will be familiar enough with the case to give a meaningful deposition on the specific testimony, including each opinion and its basis.
The expert's hourly and daily fee for deposition testimony and for consulting with the retaining attorney.

(Code Civ. Proc., § 2034.260, subd. (c).) If the demand asks for them, the experts' discoverable reports and writings are produced at the same time. (Code Civ. Proc., § 2034.270.)

The 20-day window for supplemental experts

Within 20 days after the exchange, a party that took part may serve a supplemental list naming experts on a subject an adverse party's expert will cover. This is allowed only if the party had not previously retained an expert to testify on that subject. The supplemental list needs its own declaration and reports, and those experts must be made available for deposition immediately. (Code Civ. Proc., § 2034.280.)

Expert depositions and who pays

Once a list arrives, any other party may depose the people on it. (Code Civ. Proc., § 2034.410.) The party taking the deposition of a retained expert pays the expert's reasonable and customary hourly or daily fee for the time spent at the deposition. That rule does not cover an expert who is a party or an employee of a party. (Code Civ. Proc., § 2034.430, subds. (a), (b).) An expert for whom a declaration is required must produce the materials the deposition notice calls for no later than three business days before the deposition. (Code Civ. Proc., § 2034.415.)

A party is entitled to complete expert discovery on or before the 15th day before the date initially set for trial, and to have related motions heard on or before the 10th day before that date. (Code Civ. Proc., § 2024.030.)

What happens if a party misses the exchange

The penalty is exclusion, subject to the exceptions below. On objection, the trial court must exclude the expert opinion of a witness offered by a party that unreasonably failed to list the witness, submit the declaration, produce the reports, or make the expert available for deposition. The objecting party must itself have complied completely and on time. (Code Civ. Proc., § 2034.300.)

The statute leaves three ways back in.

A party may call an expert it did not designate if another party designated that expert and the expert was then deposed. An undesignated expert may also impeach the facts another expert relied on, but may not contradict the opinion itself. (Code Civ. Proc., § 2034.310.)
A party that made a timely exchange may move to add an expert or to amend the description of an expert's testimony. (Code Civ. Proc., § 2034.610.)
A party that missed the exchange may move for leave to submit the information late. The court must find that the failure resulted from mistake, inadvertence, surprise, or excusable neglect, that the party moved promptly, and that the opponent will not be prejudiced. It may add conditions, including a trial continuance and an award of costs. (Code Civ. Proc., §§ 2034.710, 2034.720.)

How disclosure shapes a business case

In a commercial dispute, expert opinion may address damages: lost profits, business valuation, and accounting.

Experts need records and time, so retain one well before the exchange. A consultant who will not testify is not listed. The protection for that kind of advisor is covered on our page about work product.

What to bring to the first meeting

The trial setting order or notice showing the initial trial date.
Any demand for exchange of expert witness information, with its proof of service.
Expert lists, declarations, and reports already exchanged.
The damages calculation and the financial records behind it.
The names of employees who may be asked to give opinions.

Frequently asked questions

Our trial is in three months and our lawyer says expert disclosures are due. What is that and what happens if we miss it?

It is the exchange of expert witness lists that California Code of Civil Procedure section 2034.210 lets any party demand once a trial date is set. Each side names the experts it expects to call and, for retained experts, serves a declaration describing their qualifications and testimony. If your side unreasonably fails to disclose an expert, the court must exclude that expert's opinion on a proper objection.

When is expert witness disclosure due in California?

The demand sets the date. Under Code of Civil Procedure section 2034.230, the exchange is 50 days before the initial trial date, or 20 days after service of the demand, whichever is closer to the trial date. A California court can order an earlier or later date on motion and a showing of good cause.

What does CCP 2034.260 require?

Section 2034.260 of the California Code of Civil Procedure requires each party that has appeared to exchange, in writing, either a list of its expert witnesses or a statement that it does not presently intend to offer expert testimony. For retained experts, and for experts who are parties or employees of a party, a declaration under penalty of perjury must accompany the list.

When is the expert discovery cutoff in California?

Under California Code of Civil Procedure section 2024.030, a party is entitled as a matter of right to complete discovery about disclosed experts on or before the 15th day before the date initially set for trial. Motions about that discovery are to be heard on or before the 10th day before that date.

We missed the expert exchange date by a week. Can we still use our damages expert at trial?

Possibly, with the court's permission. California Code of Civil Procedure sections 2034.710 and 2034.720 allow a motion to submit tardy expert information. The court must find, among other things, that the failure resulted from mistake, inadvertence, surprise, or excusable neglect, that you moved promptly, and that the other side will not be prejudiced. The expert must be available for deposition immediately.

Talk to a California civil litigation attorney

If a trial date is set and expert disclosure is coming, or an exchange date has been missed, call (909) 235-6116 or contact us online. Kolmogorov Law, P.C. is a business litigation firm in Irvine, California.

This page provides general information about California law and is not legal advice. Outcomes depend on the trial date, the facts, and the court.