Wisconsin Statutes Civil Procedure (Ch. 799 to 847) § 807.01. Settlement offers

(1) After issue is joined but at least 20 days before the trial, the defendant may serve upon the plaintiff a written offer to allow judgment to be taken against the defendant for the sum, or property, or to the effect therein specified, with costs. If the plaintiff accepts the offer and serves notice thereof in writing, before trial and within 10 days after receipt of the offer, the plaintiff may file the offer, with proof of service of the notice of acceptance, and the clerk must thereupon enter judgment accordingly. If notice of acceptance is not given, the offer cannot be given as evidence nor mentioned on the trial. If the offer of judgment is not accepted and the plaintiff fails to recover a more favorable judgment, the plaintiff shall not recover costs but defendant shall recover costs to be computed on the demand of the complaint.

(2) After issue is joined but at least 20 days before trial, the defendant may serve upon the plaintiff a written offer that if the defendant fails in the defense the damages be assessed at a specified sum. If the plaintiff accepts the offer and serves notice thereof in writing before trial and within 10 days after receipt of the offer and prevails upon the trial, either party may file proof of service of the offer and acceptance and the damages will be assessed accordingly. If notice of acceptance is not given, the offer cannot be given as evidence nor mentioned on the trial. If the offer is not accepted and if damages assessed in favor of the plaintiff do not exceed the damages offered, neither party shall recover costs.

(3) After issue is joined but at least 20 days before trial, the plaintiff may serve upon the defendant a written offer of settlement for the sum, or property, or to the effect therein specified, with costs. If the defendant accepts the offer and serves notice thereof in writing, before trial and within 10 days after receipt of the offer, the defendant may file the offer, with proof of service of the notice of acceptance, with the clerk of court. If notice of acceptance is not given, the offer cannot be given as evidence nor mentioned on the trial. If the offer of settlement is not accepted and the plaintiff recovers a more favorable judgment, the plaintiff shall recover double the amount of the taxable costs.

(4) If there is an offer of settlement by a party under this section which is not accepted and the party recovers a judgment which is greater than or equal to the amount specified in the offer of settlement, the party is entitled to interest at an annual rate equal to 1 percent plus the prime rate in effect on January 1 of the year in which the judgment is entered if the judgment is entered on or before June 30 of that year or in effect on July 1 of the year in which the judgment is entered if the judgment is entered after June 30 of that year, as reported by the federal reserve board in federal reserve statistical release H. 15, on the amount recovered from the date of the offer of settlement until the amount is paid. Interest under this section is in lieu of interest computed under ss. 814.04(4) and 815.05(8).

(5) Subsections (1) to (4) apply to offers which may be made by any party to any other party who demands a judgment or setoff against the offering party.