1099-B Wash Sales Explained: How to Handle Them on Form 8949
Wash sales trip up even experienced investors. You sell a stock at a loss, think you've locked in the deduction, then see a mysterious number in the "wash sale loss disallowed" column of your 1099-B — and suddenly you're not sure what happened or what to do. The good news is that 1099-B wash sales follow a clear set of rules, and once you understand how they work, you can handle them correctly without much stress.
What Is a Wash Sale?
A wash sale happens when you sell a security at a loss and then buy the same or a "substantially identical" security within 30 days before or after the sale. The IRS created this rule to prevent investors from claiming artificial tax losses while keeping essentially the same investment position. If you trigger a wash sale, the IRS disallows your loss for that year.
The key phrase here is "disallowed," not "gone." This is the most important thing to understand about wash sales: the loss doesn't disappear permanently. Instead, the IRS requires you to add the disallowed loss amount to the cost basis of your replacement shares. That higher cost basis will reduce your taxable gain (or increase your deductible loss) when you eventually sell those replacement shares for good.
Simple example: You buy 100 shares of XYZ at $50 each ($5,000 total). The price drops and you sell at $40 each ($4,000), realizing a $1,000 loss. Ten days later, you buy 100 shares of XYZ again at $42 each ($4,200). Because you repurchased within 30 days, the $1,000 loss is disallowed. That $1,000 is added to your new cost basis: $4,200 + $1,000 = $5,200. Your new adjusted cost basis per share is $52.
The 30-day window runs in both directions. It's not just 30 days after the sale — it also covers 30 days before. If you buy shares on November 1 and then sell an older lot at a loss on November 15, you've already triggered a wash sale before the sale even happened. This catches many investors off guard.
How Wash Sales Show Up on Your 1099-B
Every major broker is required to report wash sales on your 1099-B, but they don't all label them the same way. Schwab typically shows a column labeled "Wash Sale Loss Disallowed." Fidelity uses similar language. TD Ameritrade and E*TRADE often use a "W" indicator next to the affected transaction.
Regardless of how your broker labels it, the underlying data maps to Box 1g on the official 1099-B form. Here's what a typical section might look like:
| Date Sold | Description | Proceeds | Cost Basis | Wash Sale Disallowed | Gain/Loss |
|---|---|---|---|---|---|
| 03/15/2025 | XYZ Corp 100 sh | $4,000 | $5,000 | $1,000 | $0 |
| 06/22/2025 | ABC ETF 50 sh | $2,300 | $2,100 | — | $200 |
Notice that in the first row, the reported gain/loss is $0, not -$1,000. The broker has already zeroed out the loss because it's disallowed. Some brokers instead show the full loss and list the wash sale adjustment separately — which is why reading Box 1g carefully matters.
When you're converting a 1099-B PDF for tax software, the wash sale amount must be preserved and mapped correctly. If it gets dropped during conversion, your reported loss will be overstated.
What You Need to Do with Wash Sale Amounts
When you report transactions on Form 8949, wash sale adjustments go in Column (g), labeled "Adjustment to gain or loss." For a wash sale, you enter the disallowed loss as a positive number in Column (g). You also enter the adjustment code "W" in Column (f).
Tax software like TurboTax, H&R Block, or TaxAct handles all of this automatically — if the wash sale data is entered correctly. The problem is that most tax software relies on import files to pull in your 1099-B data. If those files are missing the wash sale amounts, the software doesn't know to make the adjustment.
That's why accurate conversion of your broker PDF matters. The wash sale column isn't just a footnote — it's a required adjustment that affects your taxable income. Every dollar of wash sale loss that slips through uncaptured is a dollar the IRS may come back and question.
Common Wash Sale Mistakes
Mistake #1: Ignoring Wash Sales Entirely
Some investors see the "wash sale loss disallowed" column and assume it's informational only. They report the full loss anyway and wonder why they get a notice from the IRS. The disallowed amount is real and must be reflected on Form 8949. Ignoring it almost always leads to an understatement of taxable income.
Mistake #2: Double-Counting the Adjustment
Some investors correctly enter the wash sale adjustment on Form 8949 and separately adjust the cost basis of their replacement shares — effectively accounting for the same amount twice. The adjustment column on Form 8949 handles the current-year tax impact. The cost basis adjustment on replacement shares handles the future impact. Don't do both for the same transaction.
Mistake #3: Missing DRIP-Triggered Wash Sales
Dividend reinvestment plans (DRIPs) automatically buy new shares with your dividend income. If you sell shares at a loss within 30 days of a DRIP purchase of the same stock, you've triggered a wash sale — even though you didn't consciously "buy" shares. Many investors never realize DRIPs can cause this problem because the purchase feels automatic and invisible.
Mistake #4: Not Adjusting Cost Basis on Replacement Shares
When a wash sale occurs, your broker may or may not automatically update the cost basis of your replacement shares. Many do — but not all, especially if the replacement purchase happened in a different account or at a different brokerage. If your broker doesn't carry over the adjusted basis, you need to track it yourself.
Mistake #5: Assuming Wash Sales Only Apply to Identical Securities
The IRS rule covers "substantially identical" securities, which is broader than most investors expect. Selling one S&P 500 fund and immediately buying another S&P 500 fund from the same family could be considered substantially identical. Individual stocks in the same company are always identical. Options on the same stock can also be substantially identical. When in doubt, consult a tax professional.
Example: Real Wash Sale Scenario
Let's walk through a concrete example with real numbers.
Setup: On September 5, 2025, you buy 200 shares of TechCorp at $80 per share, for a total cost of $16,000. By October 3, the stock has dropped to $65. You sell all 200 shares for $13,000, realizing a $3,000 loss. On October 14 — just 11 days later — you repurchase 200 shares at $67 each, for $13,400.
Wash sale calculation: Because you repurchased TechCorp within 30 days of the loss sale, the entire $3,000 loss is disallowed. Your 1099-B will show $3,000 in Box 1g. Your adjusted gain/loss for the October 3 sale is $0.
Cost basis adjustment: Your new cost basis for the 200 shares purchased on October 14 is not $13,400. Instead, you add the $3,000 disallowed loss: $13,400 + $3,000 = $16,400. Your adjusted cost basis per share is $82.
What happens when you sell the replacement shares: Suppose in March 2026 you sell those 200 shares at $75 each, receiving $15,000. With an adjusted cost basis of $16,400, your loss is $1,400. Without the cost basis adjustment, you'd incorrectly report only a $400 loss. The wash sale rule deferred the loss, but you ultimately get credit for it.
How Our Converter Handles Wash Sales
When you upload a broker PDF to 1099-B Converter, the tool extracts wash sale amounts from Box 1g and preserves them through the conversion process. Whether you're exporting to CSV, TXF, or Excel, the wash sale column appears as a dedicated field — it doesn't get merged, dropped, or silently zeroed out.
This matters because the most common conversion problem is wash sale data getting lost when investors manually copy figures from a PDF or use generic PDF-to-CSV tools that don't understand 1099-B structure. Our converter is built specifically around brokerage tax documents, so the mapping happens automatically. You can verify the extracted amounts before importing into tax software at 1099-B Converter.
Form 8949 and Wash Sales
Form 8949 is where all capital asset sales are reported, and it's where 1099-B wash sales get their formal accounting. Each transaction from your 1099-B gets its own row on Form 8949. Column (f) takes an adjustment code, and Column (g) takes the dollar adjustment. For wash sales, you enter "W" in (f) and the disallowed loss amount as a positive number in (g).
The math works like this: if you had a $1,000 loss but $600 was disallowed as a wash sale, Column (e) shows your cost basis, Column (d) shows proceeds, and the raw difference is -$1,000. You enter $600 in Column (g), which brings your net reported loss to -$400. That $400 is what flows to Schedule D.
Schedule D then combines all your short-term and long-term capital gains and losses. The wash sale adjustment has already been absorbed at the Form 8949 level, so Schedule D doesn't need any special wash sale treatment.
FAQ: Wash Sales
Does the wash sale rule apply in tax-advantaged accounts like IRAs?
Losses inside an IRA are not deductible, so wash sales within an IRA don't create a disallowance in the traditional sense. However, if you sell at a loss in a taxable brokerage account and repurchase the same security in an IRA within 30 days, the loss is permanently disallowed — not just deferred.
What if the wash sale spans two tax years?
If you sell at a loss in December and repurchase in January within 30 days, the wash sale still applies. The disallowed loss gets added to the cost basis of the January shares. Your broker should reflect this correctly on both years' forms.
Do wash sales apply to cryptocurrency?
As of current IRS guidance, cryptocurrency is treated as property, not a "security" under the wash sale rules. Selling Bitcoin at a loss and rebuying immediately does not trigger a wash sale. However, legislation to close this loophole has been proposed multiple times.
My broker already zeroed out my loss on the 1099-B. Do I still need to report the wash sale on Form 8949?
Yes. Even if your broker's net column shows $0, you still need to report the transaction on Form 8949 with the wash sale adjustment in Column (g). The IRS reconciles what brokers report with what you file.
Can I avoid wash sales through careful planning?
Yes. The most common strategy is waiting 31 days after selling at a loss before repurchasing the same security. Some investors buy a similar-but-not-identical security during the 30-day window to maintain market exposure without triggering the rule.
Bottom Line
1099-B wash sales are confusing mostly because they're poorly explained — not because they're mathematically complex. The core idea is simple: the IRS won't let you claim a loss if you immediately repurchase the same investment, but it preserves that loss by adjusting your cost basis for the future.
The practical challenge is making sure the wash sale amounts from your broker PDF actually make it into your tax software correctly. If those numbers get dropped, you'll underreport your gains or overstate your losses. Take the time to verify your import files, or use a tool designed specifically to handle 1099-B structure.
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