California Code, Civil Code - CIV § 3291

In any action brought to recover damages for personal injury sustained by any person resulting from or occasioned by the tort of any other person, corporation, association, or partnership, whether by negligence or by willful intent of the other person, corporation, association, or partnership, and whether the injury was fatal or otherwise, it is lawful for the plaintiff in the complaint to claim interest on the damages alleged as provided in this section.

If the plaintiff makes an offer pursuant to Section 998 of the Code of Civil Procedure which the defendant does not accept prior to trial or within 30 days, whichever occurs first, and the plaintiff obtains a more favorable judgment, the judgment shall bear interest at the legal rate of 10 percent per annum calculated from the date of the plaintiff's first offer pursuant to Section 998 of the Code of Civil Procedure which is exceeded by the judgment, and interest shall accrue until the satisfaction of judgment.

This section shall not apply to a public entity, or to a public employee for an act or omission within the scope of employment, and neither the public entity nor the public employee shall be liable, directly or indirectly, to any person for any interest imposed by this section.