Rule 15.Amended and supplemental pleadings

Group III: Pleadings and Motions · Last amended March 1, 2017 · Last verified July 14, 2026

In one sentenceRule 15 lets parties amend or supplement their pleadings before and during trial, sets deadlines for responding to amendments, and defines when an amendment relates back to the date of the original pleading.

Full Text of Rule 15

Text sizeJump to: (a) (b) (c) (d)

(a) Amendments Before Trial. —

(1) Amending as a Matter of Course. — A party may amend its pleading once as a matter of course within:

(A) 21 days after serving it, or

(B) if the pleading is one to which a responsive pleading is required, 21 days after service of a responsive pleading or 21 days after service of a motion under Rule 12(b), (e), or (f), whichever is earlier.

(2) Other Amendments. — In all other cases, a party may amend its pleading only with the opposing party’s written consent or the court’s leave. The court should freely give leave when justice so requires.

(3) Time to Respond. — Unless the court orders otherwise, any required response to an amended pleading must be made within the time remaining to respond to the original pleading or within 14 days after service of the amended pleading, whichever is later.

(b) Amendments During and After Trial. —

(1) Based on an Objection at Trial. — If, at trial, a party objects that evidence is not within the issues raised in the pleadings, the court may permit the pleadings to be amended. The court should freely permit an amendment when doing so will aid in presenting the merits and the objecting party fails to satisfy the court that the evidence would prejudice that party’s action or defense on the merits. The court may grant a continuance to enable the objecting party to meet the evidence.

(2) For Issues Tried by Consent. — When an issue not raised by the pleadings is tried by the parties’ express or implied consent, it must be treated in all respects as if raised in the pleadings. A party may move — at any time, even after judgment — to amend the pleadings to conform them to the evidence and to raise an unpleaded issue. But failure to amend does not affect the result of the trial of that issue.

(1) When an Amendment Relates Back. — An amendment to a pleading relates back to the date of the original pleading when:

(A) the law that provides the applicable statute of limitations allows relation back;

(B) the amendment asserts a claim or defense that arose out of the conduct, transaction, or occurrence set out — or attempted to be set out — in the original pleading; or

(C) the amendment changes the party or the naming of the party against whom a claim is asserted, if Rule 15(c)(1)(B) is satisfied and if, within the period provided by Rule 4(w) for serving the summons and complaint, the party to be brought in by amendment:

(i) received such notice of the action that it will notbe prejudiced in defending on the merits; and

(ii) knew or should have known that the action would have been brought against it, but for a mistake concerning the proper party’s identity.

(2) Notice to the State. — When the State or a State officer or agency is added as a defendant by amendment, the notice requirements of Rule 15(c)(1)(C)(i) and (ii) are satisfied if, during the stated period, process was delivered or mailed to the Attorney General of the State or to the officer or agency.

(d) Supplemental Pleadings. — On motion and reasonable notice, the court may, on just terms, permit a party to serve a supplemental pleading setting out any transaction, occurrence, or event that happened after the date of the pleading to be supplemented. The court may permit supplementation even though the original pleading is defective in stating a claim or defense. The court may order that the opposing party plead to the supplemental pleading within a specified time.

End

Amendment History

Added February 2, 2017, effective March 1, 2017.

Plain-English Summary

Rule 15 gives parties room to fix or update their pleadings as a case develops. A party can amend a pleading once without asking permission, but only within a set window: 21 days after serving it, or if a response is required, 21 days after that response or a Rule 12 motion is served, whichever comes first. Once that window closes, the party needs either the other side's written consent or the court's permission, and courts are told to grant that permission freely when justice calls for it. If someone amends a pleading, the deadline for responding resets to the greater of the original response time or 14 days after the amendment lands.

The rule also covers what happens closer to or during trial. If a party objects that certain evidence goes beyond what the pleadings raised, the court can allow the pleadings to be amended on the spot, and should do so freely when the change helps get at the merits without prejudicing the objecting party — a continuance can buy time to respond to the new evidence. When both sides try an unpleaded issue without objection, the law treats that issue as if it had been pleaded all along, whether or not anyone bothers to formally amend. Rule 15 also spells out when an amendment relates back to the date of the original filing — a distinction that matters when a statute of limitations has since run — including the narrow path for correcting a mistaken party name, and it allows supplemental pleadings to add events that happened after the original pleading was filed.

Frequently Asked Questions

What does amending "as a matter of course" mean and how long do I have?

It means you can change your pleading without asking the other side or the court for permission. You get one free amendment within 21 days of serving the original pleading, or, if a response is required, within 21 days of the response or a Rule 12(b), (e), or (f) motion, whichever happens first.

What happens once the deadline for amending as a matter of course has passed?

You still may amend, but only with the other party's written consent or the court's leave. Courts are directed to grant leave freely when justice requires it, so a late amendment is often still available — it just needs permission first.

Can I add a new party after the statute of limitations has run?

Sometimes. Rule 15(c) lets an amendment relate back to the date of the original pleading if it grows out of the same conduct, transaction, or occurrence, and if the new party received notice of the case in time and knew or should have known it was the intended target of a mistaken identification.

What if evidence at trial does not match what was pleaded?

If a party objects, the court can still allow the pleadings to be amended to match the evidence, and should do so when it helps resolve the case on the merits without prejudicing the objecting party. If both sides try the issue without objection, the court treats it as if it had been pleaded from the start.

What is the difference between an amended pleading and a supplemental pleading?

An amendment changes or adds to what happened before the pleading was filed. A supplemental pleading adds events that happened after the original pleading, and the court can allow one even if the original pleading had defects of its own.

Source & verification. Rule text and amendment history are reproduced verbatim from the Wyoming Rules of Civil Procedure, adopted by the Supreme Court of Wyoming. Last verified July 14, 2026. · Official source

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