800-829-8310 is a real IRS phone number. It’s printed on the CP2000, the notice the IRS sends when income reported by employers, banks or other payers doesn’t match your tax return. On the CP2000 we reviewed, it appears in the “To contact us” box and again in the line “If you need assistance contact us at 1-800-829-8310.”
Updated September 25, 2026 · Checked against real notices our clients received
IRS phone number lookup
800-829-8310
✓ Real IRS number
- Who answers
- The IRS unit that handles CP2000 notices. The notice shows an “AUR control number,” short for Automated Underreporter.
- Printed on
- CP2000: “We are proposing changes to your [year] Form 1040 tax return. This is not a bill.”
- Fax
- CP2000s also list a fax number for your response. Use the one printed on yours.
- Deadline
- The response date on your notice. The one we reviewed allowed about 30 days.
- Cost
- Free. It’s a toll-free number.
A CP2000 is a proposal, not a bill
The IRS compared your return with the W-2s, 1099s and other forms it received, found a gap, and calculated what it thinks you owe. The notice says so at the top: it’s proposing changes, and it isn’t a bill yet. You get to agree, partly agree or disagree.
The one we reviewed, for a 2020 return, proposed $9,875 in total: additional tax, a substantial understatement penalty and interest.
Do you need to call 800-829-8310?
Not always. Your answer usually goes on the response form that comes with the notice, along with documents that back it up. A call helps when:
- you don’t recognize an income item the IRS listed,
- you aren’t sure how to respond, or
- something on the notice looks plainly wrong.
Have the notice, your return for that year and the income documents in question in front of you.
How to respond to a CP2000
- Check each income item the IRS lists against your records. Look for duplicates, income you reported on a different line, and forms issued under your number by mistake.
- Decide whether you agree, partly agree or disagree, and mark the response form.
- If you disagree with any part, explain why and attach proof. Keep it short and specific.
- Skip the amended return. The notice says an amended return isn’t necessary if you don’t agree with the changes. If you file one anyway, it tells you to write “CP2000” on top and attach it behind the response form.
- Send it by the response date, by mail or to the fax number on your notice, and keep proof.
What happens if you don’t respond
The CP2000 we reviewed says that if the IRS doesn’t hear back, “we’ll send you a Statutory Notice of Deficiency followed by a final bill for the proposed amount due.” A statutory notice of deficiency, such as Letter 3219, generally gives you 90 days to petition the U.S. Tax Court. After that, the IRS can assess the tax and start collecting.
About that penalty
Many CP2000s add a 20% accuracy-related penalty, often labeled a substantial understatement penalty. If you had a good reason for the mistake, you can ask for it to be removed in your response. See our guide to the substantial understatement penalty and our penalty abatement service.
If you call, plan for a wait
IRS phone lines are stretched thin. The National Taxpayer Advocate’s mid-year report covered the 2026 filing season, through April 18, 2026.
Source: IRS, IR-2026-79, National Taxpayer Advocate mid-year report to Congress (June 24, 2026).
Got a CP2000?
Let a CPA answer it for you
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800-829-8310 FAQs
Is 800-829-8310 a legitimate IRS number?
Yes. It's printed on IRS CP2000 notices, in the “To contact us” box and in the line asking you to call if you need assistance.
Is a CP2000 an audit?
Not a traditional audit. It's an automated notice from the IRS's Automated Underreporter program, triggered when third-party income reports don't match your return. It can still lead to more tax, penalties and interest, so respond by the deadline.
How long do I have to respond to a CP2000?
Respond by the date printed on the notice. The CP2000 we reviewed allowed about 30 days. If you don't respond, the IRS can send a statutory notice of deficiency and then a bill.
Should I file an amended return for a CP2000?
Usually not. The CP2000 says an amended return isn't necessary if you disagree with the changes. Use the response form and attach your explanation and documents.
Can I fax my CP2000 response?
Many CP2000s list a fax number for responses in the “To contact us” box. Use the number printed on your notice and keep the fax confirmation.
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Other numbers from IRS and state tax notices
Sources
- Redacted CP2000 received by one of our clients (PDF), dated November 28, 2022.
- Our guides to IRS Notice CP2000 and the CP2000 response letter.
- IRS, IR-2026-79 (National Taxpayer Advocate mid-year report).
Choice Tax Relief is a private tax resolution firm. We are not the IRS, the U.S. Treasury, or any government agency, and we are not affiliated with any private collection agency. You can call the IRS yourself at no charge. This page is general information, not legal or tax advice for your situation.