What is the test for awarding prejudgment interest under section 3287 of the California Civil Code?

The award or denial of prejudgment interest under section 3287, subdivision (a) presents a question of law we review de novo. (Pierotti v. Torian (2000) 81 Cal.App.4th 17, 27-28.)

Civil Code section 3287, subdivision (a) provides for the payment of prejudgment interest to every person entitled to receive damages that are certain, or capable of being made certain by calculation, if the right to receive such damages vested on a particular day. "Under [Civil Code] section 3287, subdivision (a) the court has no discretion, but must award prejudgment interest upon request, from the first day there exists both a breach and a liquidated claim." (North Oakland Medical Clinic v. Rogers (1998) 65 Cal.App.4th 824, 828.) Civil Code section 3287 does not authorize prejudgment interest where the amount of damage, as opposed to the determination of liability, "'. . . "depends upon a judicial determination based upon conflicting evidence and is not ascertainable from truthful data supplied by the claimant to his debtor.". . . '"

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