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California jury instructions / Guide

CACI No. 405 and 406: comparative fault and dividing responsibility

CACI No. 405 lets a defendant reduce an award by proving the plaintiff's own negligence helped cause the harm. CACI No. 406 has the jury assign a percentage of responsibility to everyone at fault, including people who are not in the courtroom.

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Where this applies. California only. California uses pure comparative fault; many other states bar recovery once the plaintiff's share reaches 50 or 51 percent.

Checked against. Judicial Council of California Civil Jury Instructions (CACI), 2026 edition, Nos. 405, 406 and 3902, and the July 2026 supplement, which made no change to these instructions.

California juries do not decide fault as all or nothing. When more than one person helped cause an injury, the jury assigns each a share. CACI No. 405 handles the plaintiff's own share. CACI No. 406 handles everyone else's. Together they produce the percentages on the verdict form that later shape who pays what (CACI Nos. 405 and 406).

CACI No. 405: the plaintiff's own fault

CACI No. 405 is the defendant's instruction. The defendant has to prove that the plaintiff was negligent and that the plaintiff's negligence was a substantial factor in causing the plaintiff's harm. If the defendant proves both, the plaintiff's damages go down by the percentage of responsibility the jury assigns to the plaintiff. Jurors give the percentage, and the judge calculates the reduction.

The Directions for Use set a threshold: the instruction should not be given without substantial evidence that the plaintiff was negligent. A defendant cannot get a comparative fault finding by suggestion alone.

The rule traces to Li v. Yellow Cab Co. (1975), where the California Supreme Court replaced the old contributory negligence rule, under which any fault by the plaintiff barred recovery. The court called the all-or-nothing approach inferior on logic, experience and fairness. California adopted the pure form of comparative fault, so a plaintiff found mostly at fault can still recover the share caused by others. Our guide to comparative vs. contributory negligence compares California with states that use a 50 or 51 percent bar.

CACI No. 406: dividing responsibility

CACI No. 406 does two jobs. First, if the defendant claims that someone not on trial also caused the harm, the defendant must prove that person was negligent or at fault and that the fault was a substantial factor. Second, once more than one person's fault is found to be a substantial factor, the jury gives a percentage to everyone named on the verdict form, and the shares must total 100.

The jury also makes a separate finding of the plaintiff's total damages. The instruction tells jurors not to let anyone's percentage affect that number. The split happens afterward. A business can be a person for this purpose, and the instruction includes optional language saying so.

The Directions for Use fill in the rest:

  • The instruction is built to help the jury complete verdict form VF-402, which compares the conduct of all defendants, the plaintiff and any nonparties.
  • Nonparties include anyone at fault who is not at trial, such as defendants who settled before trial and people who were never sued, citing DaFonte v. Up-Right (1992).
  • The word fault replaces negligence when someone's liability rests on another theory, such as strict products liability.
  • The defendant carries the burden of proving that other causes contributed.

Why the percentages matter: Proposition 51

The percentages do more than reduce the plaintiff's award. Civil Code section 1431.2, adopted by voters as Proposition 51, makes each defendant's liability for non-economic damages several only. A defendant pays non-economic damages in proportion to its own percentage of fault, and a separate judgment is entered for that amount (Civ. Code § 1431.2).

Economic damages work differently. The California Supreme Court explained in DaFonte, quoted with CACI No. 3902, that Proposition 51 kept joint liability among wrongdoers for provable money losses such as medical bills and lost earnings. For the intangible losses, the plaintiff now bears the risk that a responsible person cannot pay a share. This is one reason CACI No. 3902 has jurors state economic and non-economic damages separately.

The Sources and Authority for CACI No. 406 add a limit. In B.B. v. County of Los Angeles (2020), the California Supreme Court held that section 1431.2 does not let an intentional wrongdoer reduce its liability for non-economic damages based on the negligence of others.

Hypothetical example

A pedestrian in California steps off a curb while looking at a phone and is hit by a driver who was speeding. A road crew that left a sign blocking the driver's view settled before trial. The jury finds the plaintiff 20 percent responsible, the driver 50 percent and the road crew 30 percent, and sets total damages separately. The judge then applies the reduction and Proposition 51 to work out what the driver owes. This scenario is illustrative only.

Questions to sort a shared-fault case

  • Is there real evidence the plaintiff was careless? CACI No. 405 needs more than speculation.
  • Who else might share fault? List settled parties and anyone never sued.
  • Which theory applies to each person? Negligence, strict liability and intentional conduct are treated differently.
  • How are the damages split? Separate economic from non-economic losses early.
  • Can each defendant pay? Under Proposition 51, an unpaid share of non-economic damages is the plaintiff's risk.

This page explains California's official jury instructions for general readers and is legal information, not legal advice. For a case going to trial, work from the official text and consult a lawyer licensed in California.

Common questions

What does CACI No. 405 require the defendant to prove?

Two things: that the plaintiff was negligent, and that the plaintiff's negligence was a substantial factor in causing the plaintiff's own harm. If the defendant proves both, the plaintiff's damages are reduced by the percentage of responsibility the jury assigns to the plaintiff.

Who does the math when a jury finds the plaintiff partly at fault?

The judge. Under CACI No. 405 the jury states the plaintiff's percentage of responsibility, and the instruction tells jurors the judge will calculate the actual reduction.

Can a jury assign fault to someone who is not a party?

Yes, if the defendant proves that person was negligent or at fault and that the fault was a substantial factor. The Directions for Use for CACI No. 406 say nonparties can include defendants who settled before trial and wrongdoers who were never sued.

How does Proposition 51 affect a California damages award?

Under Civil Code section 1431.2, each defendant's liability for non-economic damages, such as pain and suffering, is several only and tied to that defendant's percentage of fault. The California Supreme Court has explained that joint liability remains for economic losses such as medical bills and lost earnings.

Sources

The material this guide relies on, with the jurisdiction each source covers. Links open the publisher’s own site.