Rule 12.190. Amended Pleadings
(a) Amendments. A party may amend a pleading once as a matter of course at any time before a responsive pleading is served or, if the pleading is one to which no responsive pleading is permitted and the action has not been placed on the trial calendar, may so amend it at any time within 20 days after it is served. Otherwise a party may amend a pleading only by leave of court or by written consent of the adverse party. If a party files a motion to amend a pleading, the party must attach the proposed amended pleading to the motion. Leave of court shall be given freely when justice so requires. A party must plead in response to an amended pleading within 10 days after service of the amended pleading unless the court otherwise orders.
(b) Amendments to Conform with the Evidence. When issues not raised by the pleadings are tried by express or implied consent of the parties, they will be treated in all respects as if they had been raised in the pleadings. Such amendment of the pleadings as may be necessary to cause them to conform to the evidence and to raise these issues may be made upon motion of any party at any time, even after judgment, but failure so to amend will not affect the result of the trial of these issues. If the evidence is objected to at the trial on the ground that it is not within the issues made by the pleadings, the court may allow the pleadings to be amended to conform with the evidence and must do so freely when the merits of the cause are more effectually presented thereby and the objecting party fails to satisfy the court that the admission of such evidence will prejudice the objecting party in maintaining an action or defense upon the merits.
(c) Relation Back of Amendments. When the claim or defense asserted in the amended pleading arose out of the conduct, transaction, or occurrence set forth or attempted to be set forth in the original pleading, the amendment must relate back to the date of the original pleading.
(d) Amendments Generally. At any time in furtherance of justice, upon such terms as may be just, the court may permit any process, proceeding, pleading, or record to be amended or material supplemental matter to be set forth in an amended or supplemental pleading. At every stage of the action the court must disregard any error or defect in the proceedings that does not affect the substantial rights of the parties.