In this case, plaintiff obtained a UIM arbitration award for the entire $1 million umbrella policy limit due to emotional distress plaintiff suffered from seeing the underinsured motorist hit her mother who was crossing the street with her.  Before the arbitration award, plaintiff made a 998 offer for a penny less than the umbrella policy limits, which the insurer refused.  Held, plaintiff cannot recover prejudgment interest uder Civ. Code 3291 since UIM is not a tort claim to which that section applies.  (See Pilimai v. Farmers Ins. Exchange Co. (2006) 39 Cal.4th 133.)  Plaintiff also couldn’t recover prejudgment interest under Civ. Code 3287(a) because damages were not calculable, and the 998 offer did not make them calculable.  Also, the umbrella insurer did not know before the arbitration that its policy was in play due to economic damages exceeding the primary policy’s limits.