TL;DR
- FDA's Regulatory Procedures Manual says a Warning Letter response is "usually" due within 15 working days — a strong norm, not a statutory deadline (FDA Regulatory Procedures Manual, Ch. 4).
- In October 2025, FDA gave two device firms 30 business days instead of the usual 15 — an acknowledged anomaly, not a new standard (FDA Law Blog, Oct. 2025).
- A separate 15-business-day clock covers Form 483 responses; FDA's March 2026 draft guidance says late 483 responses may not be considered before FDA decides on escalation (Federal Register, March 9, 2026).
- Missing the window isn't an automatic penalty, but FDA can proceed with further enforcement — a warning letter or import alert — without waiting for you (Alston & Bird, March 2026).
- Extensions exist but aren't guaranteed; build your CAPA response readiness before the letter arrives, not after.
How long does a company have to respond to an FDA warning letter?
You generally have 15 working days from the date on the letter to submit a written response. That's the number FDA's own Regulatory Procedures Manual uses, and it's the number nearly every Warning Letter you'll actually receive will cite. It is not, technically, a fixed legal deadline — but treating it as one is the only sane approach if you want FDA to take your response seriously.
If you're staring at a Warning Letter right now, wondering whether that 15-day clock is real or just FDA being FDA, the honest answer is: it's real enough to build your whole week around, even though the underlying language is softer than most compliance teams realize.
Is 15 working days a hard legal requirement, or just FDA's usual practice?
It's FDA's usual practice, not a statute or regulation. Chapter 4 of the Regulatory Procedures Manual says a firm should respond "usually" within 15 working days. In October 2025, FDA issued Warning Letters to two device manufacturers, FC Company and Dongguan Rainbow Tech, giving both 30 business days instead of 15, citing Quality System Regulation violations under Section 501(h) of the FD&C Act (FDA Law Blog, October 2025). The FDA Law Blog called it an anomaly, not a policy shift; the letters don't explain why those two firms got double the usual window.
Unless your own letter names a longer window, assume 15 working days is your number.
What counts as a "working day" here, and when does the clock start?
Working days means business days — no weekends, no federal holidays. Most guidance treats the clock as starting the day after you receive the letter, not the date printed on it, though the safest move is to confirm the actual receipt date in writing and count from there rather than assume.
Does a Form 483 have the same 15-day clock as a Warning Letter?
It's a related but separate 15-day window, and FDA just tightened how seriously it takes that deadline. On March 9, 2026, FDA published draft guidance, "Responding to FDA Form 483 Observations at the Conclusion of a Drug CGMP Inspection," recommending a response within 15 business days of the 483's issuance (Federal Register, March 9, 2026). The guidance states plainly that a late response may be considered untimely and may not be reviewed when FDA classifies the inspection or decides on a Warning Letter or import alert. Law firms covering the guidance describe it as FDA formalizing an expectation that used to live mostly in practice, not policy (Alston & Bird, March 2026; Cooley, April 2026).
Practically, this means your 483 response and any later Warning Letter response aren't two independent tasks on two independent clocks you can juggle loosely. A weak or late 483 response can shape whether you get a Warning Letter in the first place, and a Warning Letter response that ignores what you already told FDA in your 483 response looks inconsistent to the reviewer reading both.
What actually happens if you miss the deadline?
Nothing triggers automatically the day the clock runs out, but FDA isn't obligated to wait for you, and usually doesn't. The March 2026 draft guidance says FDA won't delay a compliance action, including a Warning Letter, to review a late 483 response. For an already-issued Warning Letter, a non-response or late response reads as a sign the firm isn't taking the findings seriously, and it costs you your best chance to shape FDA's next move before it happens.
The real risk isn't a penalty for lateness itself. It's that FDA proceeds — toward a follow-up inspection, an import alert, or escalated enforcement — using only what it observed, without your side of the story on record.
Can you get an extension?
You can ask, but don't plan around getting one. Extensions aren't a standard entitlement, and the 30-business-day cases from October 2025 were something FDA granted on its own initiative in the letter itself, not something the recipients requested afterward. If you know you'll need more time, especially for a CAPA plan requiring equipment changes or revalidation, put that request in writing early rather than letting the 15-day mark pass silently.
What should a compliance team actually do in the first 48 hours?
Start the response before you've finished being upset about the letter. Pull the inspection's Form 483, if one was issued, and check that your response stays consistent with what you're about to tell FDA now. Assign an owner for root-cause investigation on each cited CFR section immediately, not after a first meeting to discuss strategy. Fifteen working days is roughly three weeks, and a CAPA plan with real timelines and evidence of implementation takes most of that time. Teams that spend the first week deciding who's in charge routinely run out of runway before the letter is even drafted.
FAQ
Does the 15-day period apply to every FDA Warning Letter, across all product types?
The 15-working-day norm comes from FDA's Regulatory Procedures Manual and applies broadly across drug, device, and other Warning Letters, but individual letters can and occasionally do specify a different number, as seen in the October 2025 device letters that gave 30 business days. Always read the specific deadline stated in your own letter rather than assuming the general norm applies verbatim.
If I respond within 15 days, does that mean FDA won't take further action?
No. A timely, thorough response gives FDA what it needs to potentially close out the matter without further escalation, but it doesn't guarantee that outcome. FDA may still run a follow-up inspection to verify corrective actions were implemented before issuing a close-out letter.
Is the 15-day Form 483 response window the same as the Warning Letter response window?
They're separate 15-business-day windows tied to different documents. The 483 response addresses what inspectors observed on-site: the Warning Letter response, if a letter follows, addresses FDA's formal legal characterization of those violations. Under the March 2026 draft guidance, a late or weak 483 response can influence whether a Warning Letter gets issued at all.
Updated 2026-08-23: re-checked FDA's March 9, 2026 Form 483 response guidance — as of this update it remains in draft/comment status, not yet finalized, so the "draft guidance" framing throughout this piece is still accurate. No change to the 15-working-day Warning Letter response norm or the October 2025 30-business-day device-letter anomaly; no new instance of FDA granting an extended response window was found on re-verification.
Sources: FDA Regulatory Procedures Manual, Chapter 4, FDA Law Blog, October 2025, Federal Register, March 9, 2026, Alston & Bird, March 2026, Cooley, April 2026. Byline: Andy Gaber, Founder. Published 2026-07-05.