(a) A pleading may be amended 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 upon the trial calendar, the pleading may be amended at any time within thirty days after it is served. Otherwise, the pleading may be amended only by leave of court or by written consent of the adverse party; and leave shall be freely given when justice so requires. A party shall plead in response to an amended pleading within the time remaining for response to the original pleading or within ten days after service of the amended pleading, whichever period may be the longer, unless the court otherwise orders.
Rule 55.33.Amended and Supplemental Pleadings.
Part I · Rule 55: Pleadings, Motions and Hearing · Last amended January 1, 1994 · Last verified July 22, 2026
In one sentenceRule 55.33 lets a party amend a pleading once as a matter of course within set windows, otherwise only by leave of court or written consent, allows amendments to conform to evidence tried by consent, lets certain amendments relate back to the original filing date, and permits supplemental pleadings covering later events.
Full Text of Rule 55.33
(b) Amendments to Conform to the Evidence. When issues not raised by the pleadings are tried by express or implied consent of the parties, they shall 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 does not affect the result of the trial of these issues. If 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 and shall do so freely when the presentation of the merits of the action will be subserved thereby and the objecting party fails to satisfy the court that the admission of such evidence would cause prejudice in maintaining the action or defense upon the merits. The court may grant a continuance to enable the objecting party to meet such evidence.
(c) Relation Back of Amendments. Whenever 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 relates back to the date of the original pleading. An amendment changing the party against whom a claim is asserted relates back if the foregoing provision is satisfied and within the period provided by law for commencing the action against the party and serving notice of the action, the party to be brought in by amendment: (1) has received such notice of the institution of the action as will not prejudice the party in maintaining the party’s defense on the merits and (2) knew or should have known that, but for a mistake concerning the identity of the proper party, the action would have been brought against the party.
(d) Supplemental Pleadings. Upon motion of a party the court may, upon reasonable notice and upon such terms as are just, permit service of a supplemental pleading setting forth transactions or occurrences or events that have happened since the date of the pleading sought to be supplemented. Permission may be granted even though the original pleading is defective in its statement of a claim for relief or defense. If the court deems it advisable that the adverse party plead to the supplemental pleading, it shall so order, specifying the time therefor.
Amendment History
Adopted Jan. 19, 1973, eff. Sept. 1, 1973. Amended June 24, 1986 and Dec. 1, 1986, eff. Jan. 1, 1987; Amended June 1, 1993, eff. Jan. 1, 1994; Amended Sept. 28, 1993, eff. Jan. 1, 1994.
Plain-English Summary
A pleading can be amended once as a matter of course before a responsive pleading is served, or, if no responsive pleading is permitted and the case isn’t yet on the trial calendar, within 30 days after the pleading is served. Beyond that window, amendment requires leave of court or the adverse party’s written consent, and leave is to be given freely when justice requires it. A party responding to an amended pleading gets whichever is longer: the time remaining to respond to the original pleading, or 10 days after the amended pleading is served.
When issues not raised in the pleadings are tried by the parties’ express or implied consent, those issues are treated as if they had been pleaded all along. A motion to amend the pleadings to conform to that evidence can be made at any time, even after judgment, and failing to make that motion doesn’t undo the result of trying those issues. If evidence is objected to as outside the pleadings, the court can still allow an amendment and generally should when it would serve the merits and the objecting party can’t show real prejudice, granting a continuance if needed to let that party meet the new evidence.
Relation back lets an amendment reach back to the date of the original pleading when the amended claim or defense arises from the same conduct, transaction, or occurrence already set out or attempted in the original pleading. An amendment that changes the party against whom a claim is asserted relates back too, but only if that new party got notice of the action in time to avoid prejudice in defending on the merits, and knew or should have known that, but for a mistake about identity, the action would have named it in the first place.
Supplemental pleadings cover a different situation: events or transactions that happened after the original pleading was filed. On motion, with reasonable notice and on just terms, the court may permit a supplemental pleading setting those later events out, even if the original pleading was itself defective in stating a claim or defense, and the court can order the adverse party to respond to it.
Frequently Asked Questions
How many times can I amend a pleading without court permission in Missouri?
Once, as a matter of course, before a responsive pleading is served or, if none is permitted, within 30 days after the pleading is served and before the case is on the trial calendar.
What does it mean for an amendment to relate back?
The amendment is treated as if filed on the date of the original pleading, which matters for statute-of-limitations purposes, as long as it arises from the same conduct, transaction, or occurrence.
Can I amend a pleading to add a new defendant after the limitations period runs?
Possibly, if the new party got timely notice of the action and knew or should have known the suit would have named it but for a mistake about identity.
What is a supplemental pleading?
A pleading that sets out transactions, occurrences, or events that happened after the original pleading was filed, allowed by the court on motion.
What happens if issues outside the pleadings are tried without objection?
They’re treated as if they had been raised in the pleadings, and the pleadings can be amended to conform to that evidence even after judgment.
Can I amend a pleading after judgment has already been entered?
Yes, for the limited purpose of conforming the pleadings to issues that were tried by consent, even after judgment.
Source & verification. Rule text and amendment history are
reproduced verbatim from the Missouri State & Federal Court Rules, adopted by the
Supreme Court of Missouri. Last verified July 22, 2026. ·
Official source
Also known as: amended pleading Missourirelation back of amendmentssupplemental pleadingamend to conform to evidenceleave to amend freely given