Letter 12C: The IRS Needs More Information to Process Your Return

What the Letter 12C asks for

The IRS page for this letter opens with one sentence: “We need more information to process your individual income tax return.” It names three kinds of requests: missing or corrected forms or schedules that support your Form 1040 or 1040-SR, proof of your income, withholding and credit amounts, and proof of a taxpayer identification number or Social Security number.

The Internal Revenue Manual (IRM), the IRS’s staff rulebook, places the letter in original return processing. That means the IRS has not finished your return yet. The IRM also says the IRS generally keeps the return rather than mailing it back, and waits for your answer. Your letter marks the items it needs, so read it line by line before you gather anything.

The IRS page’s tips for next year point to the usual causes: entries without complete support, the wrong form or schedule for an item, and a mistyped Social Security number or individual taxpayer identification number (ITIN).

What to send, and how to disagree

The IRS page gives four steps: read the letter carefully, send the information “within 20 days,” respond even if you disagree, and do not file a Form 1040-X. If your letter prints its own reply date, use that date.

Answer every item on the letter in one reply. If you think a request is wrong, say so and explain why; the IRS page asks for “a clear explanation of what you disagree with.” Keep copies of everything you send, and note the date you mailed it. If a tax professional helps you, the IRS page notes that you can authorize someone to represent you or receive your tax information.

Why you should not file an amended return

A Letter 12C arrives while the IRS still holds your first return, unfinished. The IRS page says plainly: “Do not file a Form 1040-X, Amended U.S. Individual Income Tax Return.” Send the missing pieces with your reply instead.

The letter asks for specific items, so send those items, not a new return.

Your refund, and what happens without an answer

If you have a refund coming, the IRS page says: “We’ll send any refund due about 6-8 weeks after we receive your response.” The clock starts with your answer, so a quick, complete reply is the fastest route to the money.

This is the trap: you may get only one letter. The IRM tells IRS staff not to write a second time when a taxpayer leaves the request unanswered or answers only part of it. Staff then use the IRM’s No Reply steps: they finish your return without the missing information, which can mean they take off a credit or amount the letter asked you to support. That can shrink your refund or leave you owing. A partial answer counts the same as no answer, so send everything the letter lists.

What people mistake a Letter 12C for

Some readers take a 12C for a bill or a proposed change to their tax. It asks for information so the IRS can finish processing. A CP2000 is a different letter about income that other payers reported; our CP2000 page explains it.

Others confuse it with a letter that asks you to prove who you are before the IRS processes a return. That is a different letter, such as the Letter 5071C, with its own steps. Check the letter number in the corner of your page before you follow any advice.

If you did not file the return the letter describes, check the “not my return” box on the letter or write “not my return” in your reply. The IRM gives IRS staff separate steps for that answer.

Common Questions