We reverse the final judgment for failure to award prejudgment interest to Har-drives in its judgment against Reliance Insurance Company, the surety on a labor and material payment bond. Argonaut Ins. Co. v. May Plumbing Co., 474 So.2d 212 (Fla. 1985); Zacco Contractors, Inc. v. Irving Trust Co., 488 So.2d 616 (Fla. 3d DCA 1986). The trial court found that Reliance was required by its bond to pay Hardrives on April 8, 1986, 90 days after Hardrives performed the last of its work. The bonding company’s obligation to pay *193interest on the principal amount of the judgment runs from that date.