Form 1099-B Explained: How to Read Your Broker Report
Learn what every Form 1099-B box means, how covered and noncovered securities differ, where the numbers land on Form 8949, and how to fix common mismatches.
Form 1099-B Explained in Plain English
Form 1099-B is the tax document brokers send after you sell stocks, bonds, ETFs, or options. Certain other security types land on the same form too.
It reports sale proceeds, the cost basis your broker tracked, the holding dates, and any gain or loss calculated. The IRS receives an identical copy, which means the government already knows about your trades before you file.
Reading the form correctly tells you exactly what will flow onto Form 8949 and Schedule D.
This guide decodes every box and explains covered versus noncovered securities. It also shows how to fix the mismatches that trigger IRS notices.
When the Form Arrives and Who Sends It
Brokers must furnish 1099-B forms by February 15 of the following year. That deadline is a firm IRS rule, not a suggestion.
The IRS instructions for Form 1099-B set that deadline, though many brokers push right up against it. Some firms mail a preliminary statement first and a corrected final version weeks later.
Complex accounts with mutual funds, limited partnerships, or corporate actions are the usual delay culprits.
Filing before the final statement arrives invites an amended return later.
One form can cover dozens or even hundreds of trades for the year, so the detail pages matter. Brokers typically attach a supplemental detail statement listing every transaction, while the official 1099-B page shows the summarized totals.
Always match the summary to the detail before you report anything. Discrepancies between the two usually mean corrections arrived mid-printing.
Every Box on Form 1099-B, Decoded
The official form fits on one page, but each box carries a rule behind it. Here is the complete mapping for the boxes individual investors actually see.
| Box | What it shows | Why it matters |
|---|---|---|
| 1a | Description of the security sold | Matches the asset to your records |
| 1b | Date acquired | Drives short-term versus long-term status |
| 1c | Date sold or disposed | Sets the tax year for the gain |
| 1d | Proceeds from the sale | Your starting point for gain math |
| 1e | Cost or other basis | Subtracted from proceeds |
| 1f | Accrued market discount | Portion taxed as ordinary income |
| 1g | Wash sale loss disallowed | Loss blocked by repurchase window |
| 1h | Gain or loss already computed | Broker's math on the trade |
| 2 | Short-term or long-term checkbox | Chooses the tax rate column |
| 5 | Noncovered security checkbox | Basis may be missing or wrong |
Boxes 1f and 1g deserve special attention. Accrued market discount appears on bonds bought at a discount in the secondary market.
The wash sale box flags losses blocked because you repurchased within the window our wash sale guide explains.
Neither number changes your proceeds, but both change what you report.
Covered Versus Noncovered Securities
The covered-versus-noncovered distinction is the most important line on the form. Covered securities, meaning shares acquired after the rollout dates that began in 2011, must carry broker-reported basis. Everything else about the form hangs on that one checkbox.
Noncovered securities are older positions, transferred accounts, or certain specialty assets where the broker never had to track basis. The broker still reports proceeds for noncovered sales, but the basis field may be blank, estimated, or flatly wrong.
| Feature | Covered security | Noncovered security |
|---|---|---|
| Basis reported to IRS | Yes, in box 1e | Often blank or optional |
| Holding period | Broker determines it | You may need to document it |
| Wash sale tracking | Broker adjusts automatically | Largely your job |
| Common errors | Rare but possible | Frequent, especially on transfers |
| 8949 page | Box A or B with code blank | Box D, often with code B |
Never assume the printed basis is correct, even on covered positions. Transfer the account from another firm and basis records often arrive incomplete. Inherited stock should carry the stepped-up basis from our inherited property guide.
Yet brokers sometimes display the decedent's original cost instead. Gifted shares carry the donor's basis plus records of any gift tax paid. Verify each figure against your own statements before filing.
How 1099-B Numbers Flow Onto Form 8949
Each sale gets listed on Form 8949, with the 1099-B feeding it line by line. Sales held a year or less, with broker-reported basis, belong in Part I, box A. Sales held over a year with reported basis land in Part II, box B.
Anything carrying a noncovered flag or an adjustment code lands in box D instead.
The matching Part I box handles short-term cases, with the code letter in column F.
From there the totals combine on Schedule D, which produces the final gain or loss.
Our reporting walkthrough shows a completed example end to end.
Codes matter more than most filers realize. Code B marks a noncovered security with basis not reported to the IRS. Code W applies the wash sale disallowed amount from box 1g.
Code M or similar entries signal accrued market discount elections. Enter the code your situation requires. The IRS matches these letters against the electronic 1099-B file your broker transmitted.
The Mismatches That Trigger IRS Notices
The IRS computer compares your return against every 1099-B it received. Any gap between reported proceeds and broker-reported proceeds generates an automatic matching notice.
These notices are not audits, but they arrive with a proposed balance due. Most of them trace to a handful of preventable causes.
| Cause | What happened | Fix before filing |
|---|---|---|
| Wrong basis used | Noncovered or transferred stock | Correct box 1e with your records |
| Missing transaction | Sale reported by another broker | Include every 1099-B received |
| Duplicate entry | Corporate action restated a sale | Report the corrected single entry |
| Wash sale ignored | Repurchase inside 30 days | Apply code W adjustment |
| Options ignored | Expired or assigned contracts | Report closes and assignments |
Corporate actions cause the subtlest errors. Mergers, spinoffs, and ticker changes restate basis across new shares, and broker systems apply the adjustments at different times.
If you sold across a corporate action, reconcile the old and new share counts first. Splits and spinoffs reshuffle the per-share basis, a puzzle our cost basis methods guide untangles.
Mutual Fund Sales and Average Cost
Fund companies add one extra wrinkle to the form. Mutual fund shares default to the average cost single category method unless you elect otherwise. The 1099-B shows the averaged basis, which is legal and accepted, though it may not minimize tax.
You can instead elect specific identification by directing the fund to particular lots ahead of settlement. Meet that deadline or the fund defaults you back into averaging.
Our basis methods comparison runs the numbers for FIFO, average cost, and specific ID side by side. Once you report average cost on a return, switching away requires permission-worthy care.
What About Crypto on 1099 Forms
Digital assets moved to their own form starting with 2025 transactions. Brokers now report crypto sales on Form 1099-DA rather than 1099-B.
Our 1099-DA guide explains what each of its new boxes contains. Custodial exchanges report proceeds and, for later years, basis.
Self-custody wallets and most decentralized platforms do not receive the broker treatment, so those sales remain fully self-reported. Stock and crypto reporting now run on parallel tracks. Both roads meet at Form 8949, where your final numbers come together.
Keep Records the Broker Cannot Provide
Brokers keep required records, but your situation adds layers they never see. Save trade confirmations for noncovered positions and anything bought at a different firm. Keep estate documents, gift letters, and inheritance appraisals with the account file.
Keep the file for three years after the return is filed, or six years when basis changed materially. A five-minute scan into a yearly folder beats a April scramble through dead email accounts.
The Bottom Line on Broker Reports
Treat Form 1099-B as an input to check, never as the final word. Covered securities make filing easier because basis arrives pre-verified, while noncovered and transferred positions demand your own documentation.
Match every 1099-B to Form 8949 with the right box and codes, and the IRS matching system stays quiet. An hour of reconciliation each February protects you from notices that take months to unwind.
A Real Transaction Walked Through the Boxes
An example cements the box-by-box knowledge. Say you bought 100 shares of an ETF for $4,200 in March 2024. You then sold all 100 in June 2026 for $5,650.
Your broker reports proceeds of $5,650 in box 1d and basis of $4,200 in box 1e. Box 1b shows the March 2024 acquisition date, and box 1c shows the June 2026 sale. The short-term box sits unchecked, because more than a year passed.
Box 1h displays the broker's computed gain of $1,450. Form 8949 Part II receives that figure next, and Schedule D picks up the running total.
Now change one fact and watch the form react. If you had bought the shares in September 2025 instead, box 2 flips to short-term. The same $1,450 becomes ordinary income taxed at your wage bracket, perhaps 24 percent instead of 15 percent.
Repurchase the ETF within 30 days of the sale and box 1g wakes up. It shows the disallowed loss, and code W appears on Form 8949. One date, three different tax outcomes, all visible on the same page.
Options, Futures, and Specialty Securities
Derivative accounts generate 1099-B entries that look strange at first glance. Expired options that you sold to open appear with proceeds when you buy them back or let them expire worthless. Assigned calls settle at the strike price, which produces a two-part transaction on the form.
Regulated futures follow Section 1256 rules with a special 60/40 tax treatment. They arrive on 1099-B already marked, and our day trading guide touches on the math. Never ignore these lines just because the math looks unfamiliar.
Broad-based index options earn a special 1256 designation and are reported by the broker with mark-to-market pricing. Bond boxes fill with accrued market discount figures that need elections on your return.
Treasury interest belongs on Schedule B, not 8949, even though the sale itself appears on 1099-B. Specialty instruments reward a careful read of the supplemental statement before filing.
Handling Corrected 1099-B Forms
Brokers issue corrections more often than any filer would like. A revised statement might restate basis after a corporate action settles or fix a transfer that posted late. If you already filed with the old numbers, you generally need an amended return once the corrected form arrives.
If the correction lands before you file, simply use the final version. Ask the broker to confirm in writing which version is final when the amounts look unstable. Filing twice with different numbers is far cheaper than ignoring a correction the IRS already received.
Transferred Accounts: The Basis Trap
Switching brokers is where basis records go to die. ACATS transfers move shares cleanly, but basis history often follows months later or arrives partial. Older lots purchased before 2011 arrive noncovered no matter where they travel.
The receiving broker may guess at basis using transfer files, and those guesses flow straight onto the 1099-B. Pull the cost basis history from the old firm before transferring anything.
Then reconcile it against the new firm's records at least once a year. Correcting the record at the source prevents the mismatch from ever reaching a tax return.
Wasim Akram
Wasim researches and writes every article on TaxGainsCalc, covering capital gains tax for everyday investors. Every figure is checked against primary IRS sources before it goes live.
