Table of Contents
Quick answer: Fax your reply to the number printed on the letter itself: the IRS has no single fax number for answering letters. Put the response page or a copy of the letter on top, add copies of your documents, sign where the letter asks, and send it before the date on the letter. For a CP2000, the IRS also publishes a fax number for each processing location, listed below. For many letters, the IRS Document Upload Tool is an online alternative.
An IRS letter asking for information comes with a deadline, and mail takes days each way. Faxing gets your reply there the same day and leaves you a dated confirmation page, which is the record you want if the IRS later says it never heard from you.
Each letter routes to the team handling your case, so the fax number that counts is the one on your letter. A general number, or one meant for a form, can send your documents to a team that isn’t handling your case.
Where the fax number is
Every letter here tells you where to send your reply, though not always in the same place:
- CP2000: the processing location is printed on the top left side of the notice. Fax to that location’s number in the table below.
- CP05A: the IRS says to fax “to the fax number in the notice”.
- CP75 and CP75A: the IRS says the toll-free fax number “is shown on your notice”.
- Letter 12C: irs.gov gives no fax number and no general one exists. Use the contact details printed on the letter.
If you can’t find a fax number on your letter, call the number printed on it, or the IRS on 800-829-1040, and ask before you send. It’s also the number the IRS gives for checking a letter that doesn’t look genuine.
CP2000 fax numbers, by processing location
From the IRS page “Understanding your CP2000 series notice” (last reviewed 14 July 2026), checked on 18 October 2026. Match the location to the one printed on the top left of your notice.
| Location on your notice | Fax |
|---|---|
| Andover, MA | 877-477-9485 |
| Atlanta, GA | 877-477-0967 |
| Austin, TX | 877-477-0583 |
| Fresno, CA | 877-477-0962 |
| Holtsville, NY | 877-477-9599 |
| Ogden, UT | 877-477-9640 |
| Philadelphia, PA | 877-477-9602 |
What each letter is asking for
Four letters you can answer by fax
From each letter’s page on irs.gov, checked on 18 October 2026.
| Letter | Why you got it | What to send | Deadline |
|---|---|---|---|
| Letter 12C | The IRS needs more information to process your return, such as a missing form or schedule, or proof of income, withholding or credits | What the letter asks for. Don’t send an amended return (Form 1040-X) | 20 days |
| CP2000 | Income reported to the IRS by others doesn’t match your return | The signed response form, saying whether you agree, plus documents if you don’t | The date on the notice |
| CP05A | The IRS wants to check your income and withholding before it sends your refund | A copy of the notice and at least 3 pay stubs including the year-end one, or a letter on company letterhead. Not your W-2 | The date on the notice |
| CP75 / CP75A | The IRS is auditing items you claimed on your return | The completed response form and copies of your records | The date on the notice |
If you agree with a CP2000 and have nothing else to report, the IRS says you don’t need to amend your return. For a CP2000 that leaves you owing, the IRS notes that interest accrues until the balance is paid and penalties may apply. For a 12C, the IRS says to reply even if you disagree, and to explain clearly what you disagree with.
Putting the fax together
- Put the response page from your letter on top. If there isn’t one, use a copy of the letter’s first page. For a Letter 12C, the Taxpayer Advocate Service says to include a copy of the letter, and for a CP05A, the IRS says your reply must include one.
- Add copies of your documents, not originals, in the order the letter lists them.
- For a CP2000, put your name and Social Security number (or Taxpayer Identification Number) on each page: the Taxpayer Advocate Service asks for this on faxed replies.
- Sign and date the response form if the letter asks you to.
- Check the fax number against the letter one more time, digit by digit.
- Add a cover sheet with your name, the letter number and the page count. Our cover sheet generator makes one.
- Send it, and file the confirmation page with the letter. Then expect to wait: the IRS says about 6 to 8 weeks for a refund after a 12C reply, and to allow 60 days for a CP05A review.
Faxing or uploading?
The IRS also takes replies online. Its Document Upload Tool accepts scans and photos as JPG, PNG or PDF files, needs the access code or the letter number from your letter, and confirms that the IRS received your documents. It doesn’t take tax returns. The IRS calls it the fastest route for a CP05A, lists it for a CP2000, and gives CP75 audits an upload tool of their own; its 12C page doesn’t mention one, so check your letter.
A fax suits you if the upload tool won’t accept your letter, if your documents are on paper and you’d rather not scan them on a computer, or if you want the reply out today. Its confirmation page shows that the fax went through to the IRS number. The IRS asks anyone using an online fax service to understand that service’s privacy and security policies first.
From your phone, Municorn Fax scans the response page and your pay stubs or records with the camera, sends them to the number on your letter and keeps a confirmation page showing when the fax was delivered. The first single-page fax is free. EveryFax sends from a computer or by email.
Faxing a form rather than answering a letter? The IRS publishes fax numbers for many forms, and our IRS fax numbers by form lists them.
Frequently Asked Questions
Is there one IRS fax number for answering letters?
No. Each letter routes to the team handling your case, so use the number printed on it. CP2000 replies go to one of seven processing locations, listed above.
Should I send an amended return with my reply?
Not for a Letter 12C: the IRS says not to file Form 1040-X in reply. For a CP2000 you agree with, the IRS says you don’t need to amend your return either.
How do I know the letter is really from the IRS?
Look it up on irs.gov by its number. If it isn’t there, or something about it looks wrong, call the IRS on 800-829-1040 rather than any number in the letter.
What if I miss the deadline?
Reply as soon as you can, and call the number on the letter if you need more time. The IRS says so for CP75 audits, and that replying by the due date is what protects your appeal rights. For a CP2000, the IRS says you can send a request for more time by the same routes as a reply.
Can my tax professional reply for me?
Yes, if you authorize them. Form 2848 lets someone represent you before the IRS; Form 8821 only lets them see your tax information. Our guide to faxing Form 2848 covers sending it. The Taxpayer Advocate Service, an independent part of the IRS, also helps for free if you qualify.
Sources
- IRS, “Understanding your Letter 12C” (last reviewed 7 November 2025): 20 days, reply even if you disagree, no Form 1040-X, refund about 6 to 8 weeks after your reply; no fax number given. Checked 18 October 2026.
- IRS, “Understanding your CP2000 series notice” (last reviewed 14 July 2026): the seven processing-location fax numbers, the response form, no amendment if you agree, asking for more time, interest and penalties, online fax privacy. Checked 18 October 2026.
- IRS, “Understanding your CP05A notice” (last reviewed 25 September 2026): the documents, a copy of the notice, the fax number in the notice, 60 days, the upload tool as the fastest route. Checked 18 October 2026.
- IRS, Topic no. 654, “Understanding your CP75 or CP75A notice” (last reviewed 16 October 2026): the response form and records, the toll-free fax number on the notice, calling for more time. Checked 18 October 2026.
- IRS Document Upload Tool (last reviewed 27 August 2026): file types, the access code or letter number, confirmation of receipt, no tax returns. Checked 18 October 2026.
- IRS, “Understanding your IRS notice or letter” (last reviewed 26 May 2026): act by the due date, 800-829-1040, appeal rights. Checked 18 October 2026.
- Taxpayer Advocate Service, Letter 12C (updated 7 July 2026): enclose the information requested and a copy of the letter. Checked 18 October 2026.
- Taxpayer Advocate Service, CP2000 (updated 10 June 2026): your name and SSN or TIN on each faxed page. Checked 18 October 2026.
- IRS, “Power of attorney and other authorizations” (last reviewed 17 July 2026): Form 2848 and Form 8821. Checked 18 October 2026.
- IRS, “The Taxpayer Advocate Service is your voice at the IRS” (last reviewed 14 October 2026): independent within the IRS; its help is free. Checked 18 October 2026.
