The short version
Deadline
30 days from the date on the notice — 60 days if you are outside the United States
What it is
An automated proposal, not a determination and not a bill
If you do nothing
The IRS issues a Notice of Deficiency, which starts a 90-day clock to petition the Tax Court
Most common cause
A securities sale reported without cost basis, taxed as if the entire proceeds were profit
On this page
What a CP2000 actually is
Every year the IRS receives copies of the information returns issued in your name — W-2s, 1099s, K-1s, 1098s, brokerage statements. A computer program compares those documents against what appeared on your return. Where the totals do not match, it generates a notice proposing changes.
No person reviewed your file before that letter was printed. Nobody weighed your circumstances or looked for the deduction you were entitled to. The notice reflects what third parties reported, arranged in the least favorable way, and that is the entire extent of the analysis behind it.
This matters because it tells you what you are arguing with. A CP2000 is a proposal from a matching program. It is not a determination, it is not an audit, and the amount at the top is not a debt you owe.
Why the figure is usually inflated
The single most common example is a stock or fund sale. A broker reports the gross proceeds of the sale to the IRS. In many cases, particularly with older holdings, inherited shares, or transferred accounts, the broker does not report what you originally paid.
The matching program has no way to supply the missing figure, so it treats the cost as zero. If you sold $180,000 of stock that you bought for $172,000, the notice proposes tax on $180,000 of gain rather than $8,000. The proposed balance can run to tens of thousands of dollars for a transaction on which you barely made money.
Supplying the purchase records frequently reduces the amount to a fraction of what was proposed, and sometimes to nothing at all.
Do not pay it because it looks official. People pay CP2000 balances every year that they did not owe, because the notice reads like a demand and the figure is frightening. Work out how the number was built before you send anyone money.
What triggers one
- Securities sales without cost basis — by a wide margin the most common, and the most overstated
- A retirement distribution that was rolled over — the 1099-R reports a distribution, the rollover is not always reflected, and the whole amount looks taxable
- Contract or freelance income on a 1099-NEC that was reported on the return in a different place, or genuinely overlooked
- Equity compensation — RSU and ESPP shares where the amount already taxed through payroll gets counted a second time
- HSA or 529 distributions used for qualifying expenses but reported without that context
- A K-1 that arrived late, after the return had already been filed
- Someone else’s information return issued under your number by mistake
How to respond
The notice includes a response form with three choices: you agree, you partially agree, or you disagree. The important thing is that disagreeing is a normal outcome, not an escalation. The IRS expects responses that supply the information the matching program lacked.
- Answer within the period stated on the notice — generally 30 days from its date
- Address only the items the notice raises, and nothing else
- Attach the documents that establish your position: purchase confirmations, rollover statements, corrected information returns
- Write a short explanation tying each document to each proposed item
- Keep proof of what you sent and when, and expect the process to take months rather than weeks
If the notice also proposes an accuracy-related penalty, that penalty can be contested separately, and it frequently falls away once the underlying adjustment is corrected.
Whether to amend the return
Usually not, and this is a common and expensive mistake. A CP2000 is answered through the response process, not by filing an amended return. Filing one while the notice is open can put two inconsistent things in the system at once, and amended returns are processed slowly enough that the notice deadline will pass while you wait.
Respond to the notice. If the situation genuinely calls for an amended return, that is a decision to make with the notice deadline in view rather than instead of it.
What happens if you ignore it
The IRS issues a Notice of Deficiency. That letter starts a 90-day period to petition the United States Tax Court, and in most circuits that deadline is treated as jurisdictional — once it passes, the court generally cannot hear the case, and the tax is assessed and sent to collection.
The CP2000 stage is the cheap, informal, low-stakes opportunity to fix the problem with a letter and some paperwork. Everything after it is harder.
What to do now
Find the response deadline on the first page and diarise it. Then find the specific items the IRS is proposing to change, and locate the documents that show what actually happened. For a securities sale, that means the purchase confirmations. For a rollover, the receiving account statement.
If the amount is significant, if more than one year is involved, or if the notice touches something you would rather not explain in writing without advice, that is the point to speak with someone before responding.
This page is general information about federal tax procedure. It is not legal advice and does not account for the facts of your matter. Reviewed August 2026.
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