One Column on Form 8949 Saves You Thousands

A woman sold $200,000 worth of Bitcoin. She had bought it for $185,000. Her actual gain was $15,000. The IRS sent her a bill on the full $200,000. No human caught the error.

A computer did it. And the computer did exactly what it was told to do.

The IRS runs a program called the Automated Underreporter. AUR. It reads every form your broker sends in. It reads your tax return. It looks for gaps.

If a form says you got paid $50,000 and your return doesn't mention it, the computer writes you a letter. The letter says you owe tax on the missing money. It adds a 20% penalty. It adds interest. It mails itself.

A tax examiner reviews the file. A human checks before the notice goes out.

The IRS sends more than 4 million of these letters every year. They are called CP2000 notices. Most come from stock sales. And one in three overstates the bill.

That was before crypto.

Starting January 2026, every major crypto exchange files a new form with the IRS. Form 1099-DA. It reports the date you sold, how much you sold, and how much cash you got.

It may not report what you paid.

Not because the exchange forgot. Because the exchange is not required to fill in that box. The IRS wrote the rules. Here's what they say:

Right. So everything you bought before that date? Noncovered. The basis box stays blank. By law.

So the form lands at the IRS. It says you received $200,000. The basis box is empty.

Here is where the two pieces snap together.

The AUR computer reads the form. It sees $200,000 in proceeds. It looks for a basis. The box is blank. I mean, you know what comes next. The computer treats blank the same as zero.

So it does the math. $200,000 minus $0 equals $200,000 in gain. It writes the letter. It proposes tax on the whole thing.

You bought that Bitcoin for $185,000. Your real gain was $15,000. The machine doesn't know that. The machine can't know that. The form it reads was built with a hole in it. And the machine fills every hole with zero.

Look at what this does to real money. One CPA walked through a client's case. Actual gains: $5,500. The CP2000 proposed a tax bill, added the 20% penalty, added interest running from the original due date. Total bill: $18,070. Tax actually owed on $5,500 in gains: $825.

The client wrote a two-page letter. Filed the right form. Final bill: $915, once interest was included.

That two-page letter was worth $17,155. Sure.

This is not new. It happened with stocks.

The IRS phased in cost basis reporting for equities starting in 2011. Mutual funds in 2012. Options in 2014. Every stock bought before the cutoff date was noncovered. The broker reported proceeds but no basis. The AUR treated basis as zero. The CP2000s piled up. It became the single most common type of AUR mismatch.

Same pipe. Same joint. Same leak. They just hooked up a bigger hose.

You get 30 days to respond. That's it. If you don't answer, the IRS treats your silence as agreement. The proposed number becomes your real debt. The 20% penalty locks in. Interest keeps running from the original due date of your return. By the time you open the envelope, it has already been compounding for over a year.

Silence is the most expensive option. And it's the default.

The exit is Form 8949. Column (e). That is where you write in the basis yourself. You list what you paid. You attach it to your response. The machine didn't know. You do.

I mean, that's the whole game. The form has a hole. The machine fills it with zero. You fill it with the truth. But you have to fill it. And you have to keep the records that prove it.

That woman who sold $200,000 in Bitcoin? Her real gain was $15,000. The CPA's client owed $825. Both got bills inflated by thousands. Both fixes started the same way. One form. One column. The right number written in the right box.

The machine doesn't know what you paid. Keep the receipts.