A crypto CP2000 usually means the IRS assumed a $0 cost basis on your sales. Here's what the notice is, why it happens, and how to respond.

You get home after a long week, open the mailbox, and there's a letter from the IRS. You brace for something routine. Instead it says you owe $48,000. The catch is you spent that year dabbling in crypto across a few wallets and mostly lost money. So how can you owe tax on losses?
No. It's an automated under-reporter notice, not an audit or a final bill. The IRS computer flagged a mismatch between your return and what an exchange reported, and it's proposing a change you can dispute.
Usually because the exchange reported your gross proceeds with no cost basis, so the system assumed you paid $0. Once you supply your real purchase prices on a corrected Form 8949, the taxable amount typically drops sharply.
After the response deadline, usually 30 days, the IRS assesses the proposed tax and adds interest and penalties. Always reply by the date on the notice, even if you disagree, and send your records by certified mail.

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If that's you, take a breath. You've most likely received a CP2000 notice, and it's usually fixable. Here's what it is, why crypto triggers it so often, and how to respond.
First, a CP2000 is not an audit and it's not a final bill. It's an automated notice the IRS sends when the numbers on your return don't line up with what third parties reported about you.
When you trade on a centralized exchange, the platform files information forms (1099s) with the IRS. The IRS computer matches those against your return. Any mismatch kicks out a CP2000 proposing extra tax. It's a machine flagging a discrepancy, not a person accusing you of anything.
Most crypto CP2000s come down to one thing: missing cost basis.
Exchanges usually report your gross proceeds, the total dollar value of your sales, to the IRS. But if you moved coins into that exchange from a personal wallet or another platform, the exchange has no idea what you originally paid. When there's no cost basis on file, the system assumes it's $0.
Transfers between your own wallets make it worse. They can be counted as sales and inflate your proceeds to numbers that were never real gains. It's the same reason your 1099-DA doesn't match what you owe.
To rebuild the true picture, check three places:
Reconstructing transfers, missing basis, and messy DeFi history by hand is brutal. This is where the right tooling saves you.
A CP2000 looks scary because of the number on it, but that number is usually the IRS assuming the worst about your basis. Fix the basis and the bill often shrinks to what you actually owed, or less. Solid US crypto tax software gets you there without the manual grind.