An IRS notice is usually a proposal, not a decision. Read it before you pay it, because paying a proposal in full is agreeing to it. Most notices need an answer by a date printed on the page, and that date matters more than anything else in the letter.
The rest of this guide covers the notice people receive most often, the CP2000, how to tell when it is wrong, how to answer it, and which notices need nothing from you at all.
Read it before you pay it
When a notice arrives, people tend to do one of two opposite things. They pay it the same day to make it go away, or they put it in a drawer.
Both are mistakes, and the drawer is the worse one. Paying a CP2000 in full is accepting the IRS’s version of your return, and that version is wrong often enough to be worth reading first. Putting it away is worse, because the response date is what keeps your options open. While it has not passed, you can disagree on paper with documents. Once it has, the process moves on without you.
So the first job is always the same: find the date, find the notice number in the corner, and work out what the letter is actually proposing.
What a CP2000 is
A CP2000 is sent when the income, credits or payments reported to the IRS by third parties do not match your return. Employers, banks, brokers and payment platforms all file information returns, and the IRS matches them against what you filed.
The notice is not an audit and it is not a bill. It says what the IRS thinks is missing, what tax it proposes to add, and asks whether you agree.
When the notice is wrong
The matching is automatic, and the most common error follows directly from that.
A sale taxed as if it were all gain. A broker reports what you received when you sold shares. When the broker did not also report what you paid for them, which is common for shares bought long ago or moved between brokers, the matching treats the whole amount as profit. A sale that made little or nothing is proposed as a large gain. The fix is documenting your cost, and how cost basis works on a sale is covered in capital gains, short term and long term.
Income counted twice. The second pattern is income that was on your return, just not on the line the IRS expected. Business receipts reported on Schedule C also appear on a payment platform’s 1099-K, and the matching finds the 1099-K without recognizing it is already in your figures.
In both cases the notice is not wrong about the document. It is wrong about what the document means, and that is something only you can show.
Answering a CP2000
A CP2000 is answered on its own response form, not with an amended return.
If you agree, and you have nothing else to report, you follow the notice. The IRS says in terms that you do not need to amend your return.
If you disagree, in whole or in part, you complete and sign the response form, say which items you disagree with, and attach the documents that show it: the purchase records behind a cost basis, or the page of your return where the income already appears.
Form 1040-X comes into it only in one situation: the notice is correct, and while looking at it you find something else that also needs correcting, such as income, a credit or an expense that was left off. Then the amended return goes with the response, with CP2000 written across the top. An amended return sent on its own, in place of the response form, is not how the IRS asks for a CP2000 to be answered, and it leaves the notice itself without a reply.
If the date has already passed
A missed reply date is not the end of it, but the easy route has closed.
Where there is no reply, or the difference cannot be resolved, the IRS sends a further notice and a bill. For an income matching case, that notice is usually a CP3219A, a statutory notice of deficiency. It gives 90 days from its date to petition the US Tax Court, or 150 days if it is addressed to someone outside the United States, and the date to rely on is the one printed on the notice. Treat that date as final. If nothing is filed, the proposed changes are assessed and billed.
It is still fixable after that, through later procedures, but each one is slower than the response form was. If you are holding a CP2000 whose date has passed, the useful thing to do this week is find out which notice comes next and what date is on it.
Notices that need nothing from you
Some notices are information. A notice that your refund was changed, or that a balance has been paid, is telling you something rather than asking.
The version people miss is that “no reply needed” usually means “no reply needed if it is right”. A notice confirming a changed refund still deserves a check against your own figures, because the change may be a correction you agree with or a mistake you do not. Keep every notice with the return for that year, whichever kind it is.
Is it really from the IRS
Not every letter that says IRS on it is from the IRS. The IRS normally makes first contact by mail, through the US Postal Service, not by phone, text or email. It uses email and text only where you have opted in.
A notice can be checked. Log into your IRS online account and see whether a copy is there, or look up the notice number on irs.gov and call the number the IRS publishes, not the one printed on a letter you doubt. A demand for immediate payment by an unusual method is the clearest sign it is not real.
When it is worth having someone look at it
A single CP2000 about one missing form is often straightforward. It gets harder when the proposed amount is large, when the notice covers more than one issue, or when the date is close. Those are the files where the order of what is answered, and with what, changes the outcome, and they are part of what a back taxes engagement covers.