Written by the TaxPlain Editorial Team · Reviewed for accuracy · Last updated August 2026
⚠️ Educational only. TaxPlain does not provide tax, legal, or financial advice. Always consult a qualified tax professional about your specific situation.
What this is
Form 1099-B, "Proceeds from Broker and Barter Exchange Transactions," is the statement your brokerage sends you and the IRS summarizing what you sold during the year. Every sale of a stock, bond, mutual fund, or other security you made through that broker shows up here, along with the date, the proceeds, and — when available — your cost basis.
It's important to understand that Form 1099-B is a report, not a form you fill out yourself. Your broker generates it. What you're responsible for is using the numbers on it to correctly complete Form 8949, which then flows to Schedule D and ultimately your Form 1040.
Because the IRS receives a copy of every 1099-B directly from your broker, any mismatch between what's on the form and what you report on your return is one of the most common triggers for an automated notice.
If your broker also paid you dividends or interest during the year, those show up on separate forms — 1099-DIV and 1099-INT — not on the 1099-B, since those are income, not capital gains.
Who it affects
✓ Applies to
Anyone who sold stocks, bonds, mutual funds, or other securities through a brokerage account during the year, regardless of the dollar amount involved.
↑ Also applies to
People who transferred assets between brokers, since cost basis often doesn't transfer cleanly and shows up missing or incorrect on the new 1099-B.
📅 WHEN IT ARRIVES
Brokers are generally required to send Form 1099-B by mid-February, later than most other 1099s, because they need extra time to finalize cost basis reporting. If you file before it arrives, you risk missing corrected figures that come in a follow-up "corrected 1099-B."
Form breakdown
Form 1099-B vs. Form 8949
These two forms get confused constantly because they cover the same sales — but they serve different purposes. Form 1099-B is what your broker tells the IRS. Form 8949 is what you tell the IRS, using the 1099-B as your source data.
Form 1099-B — generated by your broker, sent to you and the IRS, one per brokerage account.
Form 8949 — filled out by you (or your software) using the 1099-B numbers, with room to correct or adjust them.
Box 1e (cost basis) — the figure your broker has on file for what you paid, if it's a covered security.
Box 12 — indicates whether basis was reported to the IRS, which determines which Form 8949 box (A, B, or C) your sale belongs in.
Corrected 1099-B — a revised version your broker may issue if figures change after the original was sent, common with mutual funds and complex securities.
One more wrinkle worth knowing: crypto exchanges are increasingly issuing Form 1099-DA instead of, or alongside, a 1099-B, since digital assets are reported under a newer set of broker rules.
When cost basis goes wrong
Missing, blank, or incorrect basis
This is the single most common source of 1099-B confusion. If your broker doesn't have a reliable record of what you paid for an asset, the cost basis box may show as blank, zero, or "not reported." That doesn't mean you owe tax on the full sale price — it means the IRS is waiting for you to supply the correct number.
Assets transferred from another broker — basis often doesn't transfer with the shares, especially for older accounts.
Inherited or gifted securities — basis usually needs to be calculated separately using date-of-death value or the original owner's basis, not whatever your broker has on file.
Employer stock plans (RSUs, ESPPs) — brokers frequently report only the amount you paid out of pocket, missing the portion already taxed as compensation, which inflates your reported gain.
Common mistakes to avoid
⚠️ TRUSTING A ZERO BASIS
Reporting a $0 cost basis when the box is simply blank overstates your gain and inflates your tax bill — track down the real purchase records instead.
⚠️ FILING BEFORE A CORRECTION ARRIVES
Brokers sometimes issue corrected 1099-Bs into March. Filing too early risks needing an amended return if the numbers change.
A less common but costly mistake: reporting a wash sale gain or loss straight off the 1099-B without checking whether your broker already applied the adjustment. Some brokers flag wash sales automatically in Box 1g, others don't — and double-counting or missing that adjustment throws off your final numbers either way.
What to do right now
Log into each brokerage account you used this year and download every 1099-B, including any corrected versions. Flag any sale where cost basis is missing or looks wrong so you can track down the real purchase records before building Form 8949.
Questions to ask your tax professional
01Is there a corrected 1099-B I should be waiting for?
02How do I calculate cost basis for inherited or gifted shares?
03Does my RSU or ESPP 1099-B correctly reflect compensation already taxed?
04Which Form 8949 box do my transactions belong in?
05What records should I keep in case my broker's basis is ever questioned?
Frequently asked questions
What is Form 1099-B used for?
Form 1099-B is issued by your broker to report the proceeds from sales of stocks, bonds, mutual funds, and other securities during the year. It often also reports your cost basis, which you need to calculate gain or loss.
What is the difference between Form 1099-B and Form 8949?
Form 1099-B is the document your broker sends you summarizing each sale. Form 8949 is the form you file with the IRS listing those same sales in detail, especially when an adjustment is needed or the basis wasn't reported. Totals from Form 8949 then flow to Schedule D.
What does it mean if my 1099-B cost basis is missing or listed as zero?
A missing or zero cost basis usually means your broker doesn't have a reliable record of what you originally paid, often because the asset was transferred in from another broker or account. You'll need to track down your own purchase records and report the correct basis on Form 8949.
Do I still need Form 1099-B if I only had a small amount of investment activity?
Yes. Brokers are required to send Form 1099-B for any reportable sale regardless of the dollar amount, and the IRS receives a matching copy, so even small transactions should be reported on your return.
Where do I get my Form 1099-B?
Your brokerage or investment platform issues Form 1099-B directly, usually available for download in your account by mid-February. It is not published as a blank form on IRS.gov since it's generated specifically for you.