(a) Amendments. A party may amend his pleading once as a matter of course at any time before a responsive pleading is filed or, if the pleading is one to which no responsive pleading is permitted and the action has not been placed upon the trial calendar, he may so amend it any time within 21 days after it is filed. Otherwise, a party may amend his pleading 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 14 days after service of the amended pleading, whichever period may be the longer, unless the court otherwise orders.
Rule 15.Amended and Supplemental Pleadings
Current through June 1, 2026 · Last verified July 10, 2026
In one sentenceRule 15 sets out when a party can amend a pleading without permission, when the court's leave is required, how amendments relate back to the original filing date for statute-of-limitations purposes, and how a party can add later-arising facts through a supplemental pleading.
Full Text of Rule 15
(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 prejudice him in maintaining his 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 Rule 4(m) for serving the summons and complaint, the party to be brought in by amendment: (1) Has received such notice of the institution of the action that he will not be prejudiced in maintaining his 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 him.
(d) Supplemental Pleadings. Upon motion of a party the court may, upon reasonable notice and upon such terms as are just, permit him to serve a supplemental pleading setting forth transactions or occurrences or events which 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
Amended effective January 1, 2012; September 5, 2013.
Plain-English Summary
Rule 15 governs changes to pleadings after they're filed. A party can amend once without asking the court, as long as no responsive pleading has been filed yet, or — if no response is allowed and the case isn't yet on the trial calendar — within 21 days of filing. After that window, amendment requires either the other side's written consent or the court's leave, which the rule directs courts to grant freely when justice calls for it. A party responding to an amended pleading gets whichever is longer: the time left to respond to the original pleading, or 14 days after being served with the amendment.
The rule also lets pleadings catch up to what happened at trial. If the parties try an issue that wasn't in the pleadings but don't object, the court treats it as if it had been pleaded all along, and either side can move to amend the pleading to match — even after judgment. If a party does object that evidence strays outside the pleadings, the court can still allow the pleading to be amended when doing so serves the merits and the objecting party can't show real prejudice, granting a continuance if needed to let that party respond to the new evidence.
Perhaps most consequential is the relation-back doctrine: an amendment that arises from the same conduct, transaction, or occurrence in the original pleading is treated as if filed on the original date — which can save a claim that would otherwise be time-barred. Relation back extends to amendments that swap in a new defendant, but only if the new party is notified of the suit and learns of the mistake in identity within the time Rule 4(m) allows for serving the summons and complaint. Separately, Rule 15 lets a party file a supplemental pleading to add events that happened after the original pleading, even if that original pleading had its own defects.
Frequently Asked Questions
How many times can I amend a pleading in Colorado without the court's permission?
You can amend once as a matter of course before the other side files a response, or within 21 days of filing if no response is allowed and the case isn't yet set for trial; after that you need consent or leave of court.
What does it mean for an amendment to relate back to the original complaint?
It means the amendment is treated as if it had been filed on the date of the original pleading, which matters when a statute of limitations would otherwise bar the new claim.
Can I add a new defendant after the statute of limitations has run?
Only if the claim against that defendant arises from the same events as the original pleading and the new defendant received notice of the suit and knew of the identity mistake within the time Rule 4(m) allows for service.
What is a supplemental pleading and how is it different from an amended one?
A supplemental pleading adds facts or events that happened after the original pleading was filed, rather than correcting or expanding on what was already alleged, and requires the court's permission.
Source & verification. The rule text is reproduced verbatim from the
official Colorado Rules of Civil Procedure (Colo. R. Civ. P. 15). Prescribed by the Supreme Court of Colorado (C.R.S. § 13-2-108; Colo. Const. art. VI). The plain-English summary is original and written by us. Last verified July 10, 2026. ·
Official source
Also known as: amend a complaint coloradoamended pleading deadlinerelation back doctrinesupplemental pleadingCRCP 15adding a new defendant after limitationsleave to amend