1099-DA Cost Basis Missing or Wrong? Here Is How to Fix It

Updated September 17, 2026. General information, not tax advice.

You opened your Form 1099-DA and the cost basis column is blank, shows zero, or is flat out wrong. The proceeds number is huge. It looks like the IRS thinks you made a fortune. Take a breath. This is the single most common problem with the new form, it is expected, and the fix happens on your return, not by fighting the exchange.

Do not file the form as-is. A 1099-DA with no basis, filed straight through, taxes you on your entire sale amount as profit. If you bought $9,000 of ETH and sold it for $10,000, the form may show $10,000 of proceeds and nothing else. Your real gain is $1,000. Reporting $10,000 as gain can cost you thousands in tax you never owed.

Why the basis is missing in the first place

Brokers only report cost basis they can see. The rules that created the 1099-DA require gross proceeds on sales from January 1, 2025, but only require basis for assets acquired in that same account on or after January 1, 2026. That leaves three big holes:

Anything you bought before 2026. Most of what people sold in 2025 was bought earlier. The broker is not required to report basis on it, and many simply leave it blank.
Anything you transferred in. Coins that came from a hardware wallet, another exchange, a friend, mining, an airdrop or a DeFi protocol arrive with no purchase record. The exchange sees an inbound transfer, not a purchase price.
Anything the broker's records got wrong. Less common, but real. Duplicate sales, a swap counted twice, or a lot matched to the wrong purchase.

Missing basis versus wrong basis: two different fixes

Missing or zero basis: fix it on Form 8949

This is the normal case and you do not need a corrected form. The IRS lets you report your own cost basis on Form 8949 as long as you have records to back it up. Exchange purchase history, wallet transaction exports, or a crypto tax software report all count as records.

Gather every source: every exchange account you have ever used, every wallet address, every chain. Not just the broker that sent the form.
Import all of it into a crypto tax tool, or build the history by hand if you have very few transactions.
Let the tool match each 2025 sale to the lots you originally bought, using a consistent method (first-in first-out is the default; specific identification is allowed if your records support it).
On Form 8949, report the proceeds that match the 1099-DA, and put your reconstructed basis in the cost basis column. Where the form left basis blank, you generally do not need an adjustment code; you are simply supplying the basis the broker did not have.
Keep the supporting records with your tax file for at least three years.

Wrong basis, wrong proceeds, or phantom transactions: ask for a corrected form

If the form reports a sale you never made, doubles a transaction, or shows a sale amount that does not match your account history, contact the exchange's support and request a corrected 1099-DA before you file. Brokers can issue corrections, and the corrected copy also goes to the IRS. If they will not correct it in time, file with the accurate numbers, attach an explanation, and keep the correspondence.

Where the fix happens: Column (e) of Form 8949 is cost basis. Column (g) is the adjustment column and column (f) is the adjustment code. For simple missing basis you fill in (e) with your real cost. For a form that reported an incorrect basis to the IRS, you report the broker's number and then use an adjustment with code B to correct it. Software fills these in for you; if you are doing it by hand, read the Form 8949 instructions for code B.

What happens if you ignore it

The IRS receives its own copy of every 1099-DA electronically and runs automated matching against your return. A return that omits reported proceeds, or reports a number that does not tie to the form, is the easiest possible thing for that system to flag. The typical result is a CP2000 notice a year or two later proposing extra tax, penalties and interest, calculated as if your basis was zero. You then have to prove the basis anyway, under a deadline, with a proposed bill on the table. Doing it correctly the first time is far less painful.

If you need more time

Reconstructing years of basis across a dozen sources can take a while. You can file for an automatic extension to October 15. An extension gives you time to file, not time to pay, so estimate what you owe and pay that by the April deadline to avoid interest.

The fastest way to fix it

Import everything into a crypto tax platform. All four tools we compare let you connect exchanges by API or CSV, add wallet addresses, and preview the matched gains for free before paying for the downloadable Form 8949. The report ties your proceeds to the 1099-DA and supplies the basis the broker could not.

Get your real number before the IRS gets theirs

Run a quick estimate with the free gains calculator, read the 1099-DA guide, or import your history into one of these and preview your gains before paying for a report.

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Frequently asked

My 1099-DA shows zero cost basis. Is the exchange wrong?

Usually not. Brokers are not required to report basis on assets bought before 2026 or transferred in from elsewhere, so they leave it blank or zero. You supply the real basis on Form 8949 from your own records.

Do I have to request a corrected 1099-DA for missing basis?

No. Missing basis is fixed on your return. Request a correction only if the proceeds, dates, or transactions themselves are wrong.

What records prove my cost basis?

Exchange purchase history, wallet transaction exports, bank records of fiat deposits, and reports generated by crypto tax software all work. Keep them for at least three years after filing.

Can I just use the form's numbers and pay the extra tax to be safe?

You can, but you would be paying tax on money you never made, often thousands of dollars. Reconstructing basis is worth the effort.

This guide is general information, not tax advice. Rules change and your facts matter. Talk to a qualified tax professional about your return. Some links on this page are referral links that may earn us a commission at no extra cost to you.