What Letter 6304-C is
Sent when a 972CG penalty is waived in full, or when a reconsideration request after assessment was incomplete and the IRS closed the case without adjustment, telling you what was missing. Reconsiderations are never suspended for more information (IRM 4.19.25.17).
Where this sits: CP2100 (the mismatch list) → B-Notices to payees → Notice 972CG a year later (the proposed penalty) → CP15 or CP215 if it isn't waived (the assessment) → CP504 if it isn't paid (collection). Letters 1948-C, 854-C and 6304-C are the IRS's replies to your 972CG response.
The deadline
None if the waiver was granted. If the case closed as incomplete, resubmit a complete request; the RSED for refund is two years from payment.
What to do
Check which of the two it is. A full waiver refunds any amount you prepaid.
Two very different letters with one number
Letter 6304-C closes a 972CG case, and it is used for the best outcome and for one of the worst. In the first, the examiner accepted your reasonable-cause statement and the proposed penalty is waived in full; the letter says so, no balance is assessed, and any amount you paid in advance is refunded with interest. In the second, you filed a reconsideration request after the penalty had already been assessed, the request was incomplete, and because reconsiderations are never suspended for more information the way an original response is, the case was simply closed without adjustment. The letter tells you what was missing but does not invite a reply. The penalty stands, interest keeps running, and collection notices continue. Read the first paragraph carefully, because the two versions look alike at a glance and payers have filed the second as good news.
If the case closed as incomplete
Nothing stops you from submitting a complete reconsideration request, so do that, addressing the stated gap and including everything from the original request as well, signed under penalties of perjury by an officer or a Form 2848 representative. If the penalty has been paid, the request should be framed as a claim for refund on Form 843, because the refund statute runs two years from the date of payment and a claim preserves Appeals and suit rights that a bare abatement request does not. If it has not been paid, decide whether to pay it first for the same reason. Check the account transcript after a full waiver to confirm the penalty and the interest both reversed and that the refund of any prepayment issued. The response guide explains what a complete request contains, the after-the-denial guide covers the reconsideration route, and the claim versus abatement page explains why the paid-or-unpaid distinction matters.
Questions about Letter 6304-C
Who receives Letter 6304-C?
Payer. Sent when a 972CG penalty is waived in full, or when a reconsideration request after assessment was incomplete and the IRS closed the case without adjustment, telling you what was missing.
What is the deadline on Letter 6304-C?
None if the waiver was granted. If the case closed as incomplete, resubmit a complete request; the RSED for refund is two years from payment.
What should I do when Letter 6304-C arrives?
Check which of the two it is. A full waiver refunds any amount you prepaid.
Is Letter 6304-C about my own income tax?
No. This decoder covers information reporting and withholding: the notices a payer, filer or payee sees because of Forms 1099, W-2, 945 and the TINs on them. Individual income-tax notices follow a different track.
Have a different notice? The IRS notice decoder lists all 77 in the order they tend to arrive.