On the paper
Read the specific item the letter asks for and the fax number or address it gives for sending it.
The letter names one or two documents, not a category. Form 8962 with the marketplace statement, a missing signature page, or a schedule that did not transmit are the usual requests. Sending the whole return again instead of the named item is the most common reason a 12C response does not close the file.
Find the date printed on your notice or letter. The paper notice and the current official IRS instructions control, even where this page differs.
Where this notice comes from
This letter comes out of return processing rather than out of examination, which is why the request is narrow and the turnaround is short.
Health insurance premium tax credit reconciliation is the most frequent trigger, followed by missing signatures, missing schedules, and identity protection PIN issues.
Because the return is not considered processed while the letter is open, the ordinary refund status tools often show nothing useful until the response is matched to the file.
The short period on this letter is a processing rule rather than a statutory one, and it exists because the return is sitting in a queue. Missing it does not forfeit a right; it sends the return down a slower path, and the IRS may process the return without the item or ask for it again.
General next steps
- Identify the exact document or figure the letter names.
- Send only that, with the copy of the letter the IRS asks you to include, by the method printed on the letter.
- Keep the transmission confirmation, because processing will not resume until the item is matched to your file.
Timing
The IRS page for Letter 12C, checked September 10, 2026, states to send the information requested within 20 days. The date printed on the notice controls; do not calculate a deadline from this page.
What Letter 12C does not mean
Letter 12C is not an audit and not a proposed change. The IRS has not questioned any figure; it cannot finish processing without the item it names. It also does not mean the refund is denied. The refund is held while the return sits unprocessed, and it moves again once the item arrives.
What this page cannot tell you
This page cannot tell you whether the document you send will satisfy the request or when processing will resume.
Official sources
If anything on this page differs from your notice or from current IRS instructions, follow the notice and the IRS.
Common questions
Should I file an amended return instead of replying?
No. The return has not been processed yet, so there is nothing to amend. The letter asks for a specific item to be added to the pending return.
Why is my refund status showing nothing?
The return is not processed while the request is open. The status tools generally show movement again only after the response is matched to the file.
Does replying restart the refund timeline?
Processing resumes when the response is matched to the pending return. The IRS does not treat the reply as a new filing, so the return keeps its original filing date for the purposes that depend on it.
What if I do not have the document the letter asks for?
Obtain it from the issuer where possible; marketplace statements and wage statements are reissued on request. If it does not exist, the letter's contact instructions are the route for explaining that.