Affirming a district court's confirmation of an arbitration award, the Idaho Supreme Court held that an arbitrator's award of prejudgment interest, though improper, was not a "miscalculation of figures" and thus not grounds for modifying an arbitration award under Idaho law.

In Cranney v. Mutual of Enumclaw Ins. Co., No. 33501, 2007 WL 4472242 (Idaho Dec. 24, 2007), the Cranneys were involved in a car accident. They were unable to reach an agreement with their insurer about coverage and sued. Mutual of Enumclaw moved to compel arbitration, as the insurance contract contained an arbitration agreement. The district court granted the motion and stayed judicial proceedings.

After the arbitrator awarded damages, including $61,262 in prejudgment interest, to the Cranneys, they moved to confirm the award. Mutual of Enumclaw objected, arguing the arbitrator had incorrectly calculated prejudgment interest. The district court confirmed the award and awarded court costs to the Cranneys. Mutual of Enumclaw appealed, arguing the district court erred by not modifying the arbitrator's award of prejudgment interest.

The Court held that an arbitrator's improper award of prejudgment interest was not a basis for modifying an arbitration award under Idaho law. Although Idaho Code § 7-913(a)(1) permits a court to modify an award for "an evident miscalculation of figures," the error "must be a mathematical error in calculating the amount of an award, not a legal error in the elements or measure of damages when making the award." Because the arbitrator's award of prejudgment interest was a legal error rather than a mathematical one, the trial court properly declined to modify the arbitrator's award.