Rule 15.Amended and supplemental pleadings.

Rule 15(a) allows a party to amend a pleading once as a matter of course at any time before a responsive pleading is served, or, for a pleading that permits no response and whose action is not yet calendared for trial, within 30 days after it is served. Beyond that window, amendment requires either leave of court or the adverse party’s written consent, and leave is to be freely given when justice requires it. A party must respond to an amended pleading within 30 days of its service, unless the court orders otherwise.

Rule 15(b) addresses issues that come up at trial without having been raised in the pleadings: if the parties try them by express or implied consent, they are treated in every respect as if the pleadings had raised them, and the pleadings may be amended to conform to the evidence at any time, before or after judgment, though failure to amend does not affect how those issues were tried. If a party objects that evidence falls outside the pleaded issues, the court is to freely allow amendment when doing so serves the merits and the objecting party cannot show the new evidence would cause real prejudice, and the court may grant a continuance to let that party respond to it.

Rule 15(c) gives an amended pleading the same effective filing date as the original — a claim in the amendment relates back to when the original pleading was filed — unless the original pleading failed to give notice of the transactions or occurrences the amendment now seeks to prove. Rule 15(d) separately allows a supplemental pleading, on motion, reasonable notice, and terms the court finds just, to add transactions, occurrences, or events that happened after the pleading being supplemented was filed, whether or not that original pleading was itself defective, and the court may order the adverse party to respond to it on a set timetable.