A CP2000 is a proposal. You are allowed to disagree with it.

What the notice means

The IRS Automated Underreporter program compares the income on your return with information returns from payers: Forms W-2, 1099-NEC, 1099-K, 1099-B, 1099-INT, 1099-R, and others. When the totals differ, the system generates a CP2000 that lists each mismatched item, recalculates your tax, and proposes the difference.

The proposal is often wrong, or right on the income and wrong on the tax. Common reasons:

• Brokerage sales reported without basis. A Form 1099-B shows gross proceeds. If the basis never reached the IRS, the notice treats the entire sale price as gain.
• Form 1099-K gross amounts. Payment platforms report gross receipts, including refunds, fees, and personal transfers that are not income.
• Income reported on a different line. You reported it, but on a schedule the matching program did not connect to the payer's form.
• A payer's error or a duplicate form. A corrected 1099 was never filed, or the same income was reported twice.
• Identity theft. Someone else earned income under your Social Security number.
• Income that was truly left off. In that case the question becomes deductions, withholding credits, and the penalty.

The deadline

The response date is printed on the first page, generally 30 days from the date of the notice (60 days if you live outside the United States). You can ask for more time, and the IRS often grants one extension, but the request should be made before the date passes, and in writing or with a record of the call.

Your three response options

• Agree. Sign the response form. The IRS assesses the tax, penalty, and interest, and you can pay or ask for a payment arrangement.
• Partially agree. Accept the items that are right, contest the ones that are not, and attach proof for each contested item.
• Disagree. Explain why in a signed statement and attach the documents that prove it: corrected forms, basis records, account statements, a letter from the payer.

A useful response is organized item by item in the same order the notice uses, so the examiner reading it can close each line. A disorganized response tends to produce a second notice repeating the first.

What happens if you ignore it

Silence is treated as agreement in practice. The IRS issues a statutory notice of deficiency (often Notice CP3219A), which gives you 90 days to petition the U.S. Tax Court. If that window also closes, the tax is assessed, a bill follows, and the account moves into collection, where the tools are levy notices, bank levies, and wage garnishment.

The penalty is a separate fight

Most CP2000 notices add a 20 percent accuracy-related penalty for a substantial understatement. That penalty is not automatic in law even when it is automatic in the software. It can be contested on reasonable cause, and the underlying procedural requirements for asserting it can be examined. On a large adjustment, the penalty is frequently the most negotiable number on the page.

When a lawyer matters

Many small CP2000 notices can be answered without counsel. A lawyer earns the fee when the proposed amount is large, when the same problem repeats across several years, when the missing income is real and you are worried about how it looks, or when the unreported item came from a business, crypto activity, or a foreign account. Conversations with an attorney about those facts are privileged. Conversations with a tax preparer about them may not be.