What is a 1099-B, and what do I do with it?
The form your broker sends each year listing every sale, with what you paid, what you received and how long you held. You use it to report capital gains and losses on your tax return.
Form 1099-B is your broker’s annual report of everything you sold. For each sale it shows the date you bought, the date you sold, what you paid (the cost basis), what you received, and whether the holding was short- or long-term. Your broker sends a copy to you and to the IRS, usually by mid-February, often bundled with the 1099-DIV for dividends into one "consolidated 1099."
You use it to fill in Schedule D and Form 8949 on your return, which is where capital gains and losses are reported. Tax software imports the form directly from most brokers, so in practice you log in, click import, and check that the totals look right.
If you did not sell anything during the year, you may not get a 1099-B at all, or it will be blank. Dividends and interest come on separate forms regardless of whether you sold.
One thing to check: the cost basis. For shares bought before 2011, or transferred between brokers, the basis can be missing or wrong, and a missing basis makes the IRS assume you paid zero, taxing the entire sale as profit. If a line shows no basis, dig out your original purchase records.
Informational only, not financial advice. Updated September 4, 2026.
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