IRS & CT DRS Tax Letters Explained › Letter 12C
IRS Letter 12C Explained: The IRS Needs More Information
By Andrew Nocera, Tax Preparer & Small-Business Finance Consultant, Enhance Finance LLC (serving all of Connecticut from Shelton). Updated November 2026.
Letter 12C means the IRS can't finish processing your individual return until you send it something: a missing form or schedule, or proof of income, withholding, credits or identification numbers. Answer it quickly; any refund waits until you do.
IRSWe can help with this| What it is | Request for missing or corrected information on your Form 1040 or 1040-SR. |
|---|---|
| Deadline | "Send the information we requested within 20 days." |
| Official page | IRS: Understanding your Letter 12C |
What Letter 12C is
The IRS says: "We need more information to process your individual income tax return." It lists what that could be:
- Missing or corrected forms or schedules to support your entries on Form 1040 or Form 1040-SR.
- Verification of income, withholding and credit amounts.
- Verification of taxpayer identification numbers or Social Security numbers.
Why you got it
Something on your return needs support before the IRS can finish. The letter itself lists exactly what's missing. Typical examples are a schedule that should have been attached, withholding the IRS needs to verify, a credit that needs a supporting form, or an SSN or ITIN that needs checking.
Deadline
What to do, step by step
- Read the letter carefully and list every item it asks for.
- Gather the documents: the missing form or schedule, W-2s, 1099s, support for credits, or proof of identification numbers.
- Include the letter's reply instructions and any response page it came with, so your documents get matched to your return.
- Disagree with what they're asking? The IRS says to respond anyway, "providing a clear explanation of what you disagree with."
- Send it the way the letter instructs, within 20 days, and keep a copy of everything you send and the date.
- Don't file an amended return. The IRS says: "Do not file a Form 1040-X, Amended U.S. Individual Income Tax Return."
Common mistakes
- Filing Form 1040-X instead of answering the letter.
- Sending only part of what was asked, which can mean more letters and a longer wait.
- Missing the 20-day window.
- Not keeping copies of what you sent and when.
- Not replying because you disagree. Reply with your explanation.
When to get help
Get help if you aren't sure which form or schedule the IRS wants, the numbers you reported don't match your documents, or whoever prepared the return isn't responding. We can help you read the letter, pull together the right forms and draft a response for you to send.
General information, not advice for your situation. Not tax, legal, investment, or insurance advice. Agency rules and procedures change; always follow the instructions and dates on your own notice and check the official sources below.
Frequently asked questions
How long do I have to answer Letter 12C?
The IRS says to send the information it requested within 20 days.
When will I get my refund after answering Letter 12C?
The IRS says it will send any refund due about 6 to 8 weeks after it receives your response.
Should I file an amended return?
No. The IRS says do not file Form 1040-X. Send the information the letter asks for instead.
What if I disagree with the letter?
Respond anyway. The IRS says to respond even if you disagree, with a clear explanation of what you disagree with.
Sources (checked November 10, 2026)
- IRS, Understanding your Letter 12C (what may be needed, 20 days, refund about 6-8 weeks after response, respond even if you disagree, do not file Form 1040-X): www.irs.gov
Not sure what the IRS is asking for? Go through Letter 12C with a Connecticut tax preparer.