The LTR 12C is one of the most common letters the IRS sends, and it's usually the easiest to resolve. The IRS received your tax return but can't finish processing it because something is missing. They need documents from you before they can move forward.
The letter tells you exactly what they need. Your job is to send it. All of it. The first time.
What the IRS Typically Requests
The LTR 12C usually asks for one or more of the following: a copy of your W-2 that the IRS didn't receive from your employer, documentation supporting a credit or deduction you claimed, proof of income or withholding, verification of your filing status or dependents, or a signed copy of your return if the original wasn't signed.
The letter lists each item the IRS needs. Read the list carefully. Every item matters. If they ask for three documents, sending two of them means you'll wait another 8 to 12 weeks for the IRS to process what you sent, determine it's incomplete, and send you another letter asking for the missing piece.
How to Respond
Gather every document the letter requests. Make copies of everything. Include the tear-off stub from the bottom of the letter with your response. That stub contains your identifying information and helps the IRS match your response to your account.
Send your response to the address on the letter. Not to a general IRS address. Not to the address you used for your tax return. The address on the letter routes your response to the specific processing center handling your case.
Use certified mail with return receipt. The IRS processes millions of pieces of mail. Things get lost. Your certified mail receipt is proof that they received your response and when. That proof can be worth thousands if there's ever a dispute about whether you responded on time.
Common Mistakes
The number one mistake is sending a partial response. You send two of the three requested items, thinking the third one will follow next week. It doesn't. Or it does, but the IRS has already processed your partial response and sent a new letter asking for what's missing. Now you've added 8 to 16 weeks to the timeline.
The number two mistake is sending documents for the wrong tax year. If the letter is about your 2024 return, don't send your 2023 W-2. Check the tax year on every document before you mail it.
The number three mistake is not including the tear-off stub. Without it, your response goes into a pile of unidentified correspondence waiting for manual matching. That can add weeks to processing.
How Long Does Processing Take
After the IRS receives your complete response, allow 6 to 8 weeks for processing. If your return was filed electronically and you're waiting for a refund, the refund clock restarts after your response is processed. If you filed on paper, it may take longer.
Check your IRS Online Account or call the IRS after 8 weeks if you haven't received your refund or a follow-up letter. Have your copies ready so you can reference exactly what you sent and when.
The Bottom Line
The LTR 12C is not scary. It's a documentation request. Send everything they ask for, send it on time, and keep copies. If you're not sure what they're asking for, call the number on the letter or call us at (813) 229-7100. A quick review of the letter can save you months of back-and-forth.