Amending a federal pleading: the 21-day window, leave to amend, and the scheduling order that outranks both

Rule 15 is generous. Rule 16 is not. Which one governs an amendment depends on whether the scheduling order's deadline has passed, and that is the single most consequential thing to know about amending in federal court.

One amendment as of right

Rule 15(a)(1): a party may amend its pleading once as a matter of course no later than:

• 21 days after serving it; or
• 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.

Three things follow.

Once. The as-of-right amendment is a single use, not one per responsive pleading.

Whichever is earlier. A defendant who answers and later moves under Rule 12(f) doesn't reset the plaintiff's window; the earlier of the two triggers starts it.

A Rule 12 motion starts the clock too. A plaintiff facing a motion to dismiss has 21 days from service of that motion to amend without asking anyone — which is often a better answer to a well-taken Rule 12(b)(6) motion than opposing it.

After that — leave, freely given

Rule 15(a)(2): "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."

Two routes, and the first is often overlooked: written consent from the opposing party needs no motion at all.

"Freely give leave when justice so requires" is among the most permissive standards in the rules. Federal courts nonetheless deny leave for reasons developed in case law — undue delay, bad faith, repeated failure to cure, undue prejudice, and futility. Those factors are not in the rule's text.

Responding to an amended pleading

Rule 15(a)(3): 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.

So an amendment served late in the original response period buys the responding party at least 14 days, and never less than what was left.

Where Rule 16 takes over

Rule 16(b)(3)(A): a scheduling order "must limit the time to join other parties, amend the pleadings, complete discovery, and file motions."

Every federal case with a scheduling order therefore has an amendment deadline. And Rule 16(b)(4): "A schedule may be modified only for good cause and with the judge's consent."

After that deadline, a party seeking to amend has to satisfy Rule 16's good-cause standard before Rule 15's liberal standard is even reached. Good cause under Rule 16 focuses on the diligence of the party seeking the amendment — a different question from whether the other side would be prejudiced.

Rule 16(b)(2) sets when the order arrives: the judge must issue it as soon as practicable, and unless there is good cause for delay, "within the earlier of 90 days after any defendant has been served with the complaint or 60 days after any defendant has appeared."

That is the practical sequence. Rule 15 governs early; the scheduling order takes over within about three months of service; and from then on the first question about any amendment is whether the deadline has passed.

Relation back — Rule 15(c)

Whether an amendment relates back to the date of the original pleading decides whether a claim added after the limitations period is time-barred.

Rule 15(c)(1) gives three routes:

(A) The limitations law allows it. "[T]he law that provides the applicable statute of limitations allows relation back." In a diversity case this can make state relation-back law available where it is more generous.

(B) Same conduct, transaction, or occurrence. 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." Note "or attempted to be set out," which reaches an original pleading that described the events badly.

(C) Changing the party. An amendment changing the party, or the naming of the party, against whom a claim is asserted relates back if (B) is satisfied and, within the Rule 4(m) service period, the party to be brought in:

(i) received such notice of the action that it will not be 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.

Two conditions, both within the Rule 4(m) window, and the second is about a mistake of identity — not about a plaintiff who simply hadn't yet identified whom to sue.

Rule 15(c)(2) supplies a special rule where the United States or a federal officer or agency is added by amendment: the notice requirements of (c)(1)(C)(i) and (ii) are satisfied if, during the stated period, process was delivered or mailed to the United States attorney or their designee, to the Attorney General, or to the officer or agency.

Amending at and after trial

On an objection at trial — Rule 15(b)(1). If a party objects that evidence is not within the issues raised in the pleadings, the court may permit amendment, and "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 let the objecting party meet the evidence.

Issues tried by consent — Rule 15(b)(2). When an issue not raised by the pleadings is tried by 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 to the evidence. And failure to amend "does not affect the result of the trial of that issue."

Supplemental pleadings are different

Rule 15(d): 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.

An amended pleading replaces and covers the same period. A supplemental pleading adds later events. Rule 15(d) always requires a motion — there is no supplement as of right.

The order of questions

1. Is this within 21 days of serving the pleading, or of service of a responsive pleading or a Rule 12(b), (e) or (f) motion — and is it my one as-of-right amendment? → Rule 15(a)(1), just file it.
2. Will the other side consent in writing? → Rule 15(a)(2), no motion needed.
3. Has the Rule 16(b) amendment deadline passed? → good cause and the judge's consent first, then Rule 15.
4. Is limitations in play? → Rule 15(c), and for a party change, check the Rule 4(m) window.
5. Are these events that happened after the pleading? → Rule 15(d), by motion.

Where these rules live

• Rule 4 — Summons
• Rule 12 — Defenses and Objections
• Rule 15 — Amended and Supplemental Pleadings
• Rule 16 — Pretrial Conferences; Scheduling; Management
• Rule 26 — Duty to Disclose; General Provisions Governing Discovery

This page explains what the rules say. It isn't legal advice, and the factors courts weigh in deciding whether to give leave come from case law this site doesn't cover.