Wash Sale on Form 8949: Code W and Column (g)

It is a familiar December ritual. An investor looks at a broad-market fund sitting at a loss, decides to harvest the deduction before year-end, and sells the whole position. A few days later, wanting to stay invested, they buy back a near-identical fund — same index, different ticker, or in many cases the very same fund. Nothing about the trade feels wrong. Then the next February the consolidated Form 1099-B arrives, and a number the investor never expected is sitting in a box labeled “Wash sale loss disallowed.” The loss they thought they had banked has been quietly clawed back.

That box is the broker telling you the Internal Revenue Service will not let you deduct the loss this year, because you replaced the security too soon. The rule is unforgiving in its timing and easy to trip without noticing — automatic dividend reinvestment alone can spring it. But the loss is not necessarily lost, and reporting it correctly on Form 8949 hinges on one instruction that runs against every other adjustment on the form.

The short answer: report the sale normally, then put the code “W” in column (f) of Form 8949 and enter the disallowed loss as a positive number in column (g). That positive figure cancels the loss, so the line nets to zero. The disallowed amount is not gone — it is added to the cost basis of your replacement shares and the old holding period carries over, so you recover the loss when you later sell those shares in a taxable account. The one exception that turns a deferral into a permanent loss is buying the replacement inside an IRA.

What counts as a wash sale

The wash sale rule lives in section 1091 of the Internal Revenue Code. It disallows a loss if you buy substantially identical stock or securities within 30 days before or 30 days after the sale that produced the loss. Count both directions and you get a 61-day window centered on the sale date — the day of the sale, plus the 30 days on either side. The “before” half catches people most often, because they assume only purchases after the sale matter.

Two phrases carry the weight. “Substantially identical” is broader than identical: the same fund bought back is plainly caught, and two funds tracking the same index can be caught too, though a genuinely different fund usually is not. And the window applies across all of your accounts, not just the one where the loss occurred. A sale in your taxable brokerage paired with a purchase in your spouse’s account or, critically, in your IRA, still triggers the rule. IRS Publication 550 walks through the details and the edge cases.

Reading box 1g on your 1099-B

Your broker does part of the work for you. On the Form 1099-B inside your consolidated tax statement, a wash sale your broker can see appears in Box 1g, “Wash sale loss disallowed.” The amount shown there is the portion of your loss the broker has determined is nondeductible — and it is the number you will carry straight into column (g) of Form 8949.

One caveat worth keeping in mind: a broker only tracks wash sales within the accounts it holds, on identical securities (same CUSIP). It cannot see a replacement purchase you made at another firm or in your IRA, so box 1g can understate the disallowed amount. When the trade crosses accounts, the responsibility to catch it is yours, not the broker’s.

The Form 8949 entry, column by column

Suppose you sold 100 shares of a fund for $4,000 that you had bought for $5,000 — a $1,000 loss. Your broker stamps box 1g with $1,000, disallowing the entire loss because you rebought within the window. Here is how the line reads on Form 8949:

(a) Description	(d) Proceeds	(e) Cost basis	(f) Code	(g) Adjustment	(h) Gain/(loss)
100 sh Fund XYZ	4,000	5,000	W	1,000	0

Column (h) is computed as proceeds minus basis, plus the adjustment: $4,000 − $5,000 + $1,000 = $0. The loss has been neutralized for this tax year.

Now the part that trips everyone. Most adjustments in column (g) are negative, because they reduce a gain — that is the usual reason to adjust a line at all. A wash sale is the opposite case: you are adding the disallowed loss back, so the adjustment moves the result up toward zero rather than down. The IRS instruction is unambiguous on this point. Per the Instructions for Form 8949, when you use code W you “enter the amount of the nondeductible loss as a positive number in column (g).” A positive number, added to a negative loss, is what cancels it.

Where the loss goes: basis of the replacement shares

The disallowed loss does not evaporate. Section 1091 redirects it: the $1,000 you could not deduct is added to the cost basis of the replacement shares, and the holding period of the shares you sold tacks onto the new lot. The deduction has been moved, not destroyed.

Carry the example forward. You sold the original 100 shares for $4,000 against a $5,000 basis, and you bought 100 replacement shares for, say, $4,100. Normally your basis in the new lot would be that $4,100. Because of the wash sale, you add the $1,000 disallowed loss, so your true basis becomes $5,100. Later, in a year with no wash sale, you sell those replacement shares in your taxable account for $6,000. Your gain is $6,000 − $5,100 = $900, not the $1,900 a $4,100 basis would have produced. That extra $1,000 of basis is the original loss, finally doing its job. The wash sale rule delayed your deduction; it did not deny it.

The IRA trap

There is one place this clean deferral breaks down completely, and it is the costliest wash-sale mistake there is.

The mechanics are unforgiving. Sell a fund in your taxable brokerage at a $1,000 loss in December, let your IRA’s automatic investment buy the same fund three days later, and that $1,000 is simply gone — disallowed in the taxable account, with nothing in the IRA to attach it to. Unlike the ordinary case, waiting to sell the IRA shares recovers nothing.

Avoiding the trap

The fix is mostly about timing and awareness. Wait at least 31 days after the sale before buying the security back, which clears the window on the “after” side, and check that nothing bought it for you in the 30 days before. Alternatively, buy a genuinely different fund — one tracking a different index, not a near-clone — to stay invested without replacing the security. Two automatic triggers deserve a standing watch: dividend reinvestment, which can buy a few shares inside the window without your noticing, and purchases in your other accounts, above all your IRA, where the loss does not merely defer but disappears.