Missing forms or schedules
A required attachment may be absent, damaged, incomplete, unsigned, or illegible.
IRS Letter 12C • Missing Information
Received IRS Letter 12C?
The IRS received your individual income tax return but needs missing, corrected, or verifying information before it can finish processing it.
Respond within 20 days. Send only what the letter requests. Do not file Form 1040-X and do not send another complete return unless the IRS specifically asks for it.
There is no fee to book the call. No documents are required when booking. Have the complete Letter 12C and filed return available during your call.
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What Letter 12C Means
The return cannot be processed accurately yet
The IRS may need a missing schedule, a corrected form, verification of income or withholding, complete taxpayer identification numbers, or Premium Tax Credit information.
Letter 12C is not an amended-return request. The IRS will use the response to continue processing the original return.
Common Requests
Why the IRS may send Letter 12C
Income verification
The IRS may ask for Forms W-2, 1099, or records supporting income reported on the return.
Withholding verification
The IRS may need proof of federal income tax withheld before allowing the claimed amount.
Premium Tax Credit
Form 1095-A or Form 8962 may be needed to reconcile Marketplace health insurance information.
Taxpayer identification
A Social Security number or individual taxpayer identification number may be missing or inconsistent.
Credit support
The IRS may need records or schedules supporting a credit claimed on the return.
How To Respond
Send only the requested information
Follow each numbered request
Organize the response in the same order as the items listed in Letter 12C.
Include a copy of the letter
Use the response method and identifying information shown on the letter so the IRS can match the records to the return.
If you disagree
Respond within the deadline with a clear explanation and the records supporting your position.
Records To Review
Have these available for the call
- Every page of Letter 12C
- The filed federal return and schedules
- The specific forms and schedules requested
- W-2s, 1099s, and withholding records
- Form 1095-A and Form 8962, if requested
- Documents supporting the questioned credit
- Correct identification information
- Proof and explanation for any disagreement
Avoid Duplicate Filing
Do not send an amended or duplicate return
The IRS instructs taxpayers not to file Form 1040-X in response to Letter 12C. Do not send another full copy of the original return unless the letter asks for it. A duplicate filing can create additional processing problems.
Response Quality
Make the submission easy to match and review
Use complete, readable copies
Make sure every page is legible and that names, tax year, amounts, and identification information match the return and letter.
Keep proof of submission
Retain the complete response and confirmation, fax transmission report, or mailing proof permitted by the letter instructions.
What Happens Next
The IRS will review the response
Return processed
The IRS may use the response to finish processing the original return.
More information requested
The IRS may ask for additional explanation or documentation.
Return adjusted
If the response is missing or insufficient, the IRS may reduce the refund or increase the tax.
Frequently Asked Questions
IRS Letter 12C questions
Is Letter 12C an audit?
Not generally. It is a request for information needed to process the original return accurately.
Should I file Form 1040-X?
No. The IRS specifically says not to file an amended return in response to Letter 12C.
Should I send my whole return again?
No, unless the letter specifically asks for it. Send only the requested information and a copy of Letter 12C.
What if I do not respond?
The IRS may adjust the return, reduce the refund, or increase the tax based on the information available.
Is there a fee to book?
No. There is no fee to book the call. Professional work requires a separate written engagement.
Can TaxDecoders help?
Assistance may be offered after the letter, deadline, filed return, requested forms, and supporting records are reviewed.
Verified Resources
Official IRS information
This page was reviewed on July 27, 2026. Always follow the date and instructions printed on your actual letter.
Understanding Letter 12C
Taxpayer Advocate roadmap
Marketplace statements
Respond correctly so the IRS can finish processing the return.
Book a call with TaxDecoders. Have the complete Letter 12C, filed return, and the specific forms or records requested available during the call.
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