"Wash sale loss disallowed" on your 1099-B, decoded
By the Wash-Sale Guardian team · Published 2026-07-14 · Last updated 2026-07-14 · How we check our facts
Short answer: "wash sale loss disallowed" (Form 1099-B, box 1g) is the loss your broker couldn't let you deduct because you re-bought the same security within the 61-day window — in that account. It's usually a deferral, not a destruction: the amount was added to your replacement shares' basis per IRS Pub 550, and you recover it when you exit cleanly. The dangerous parts are what box 1g does NOT include.
Why the number can be shockingly large
Active traders re-buying the same ticker roll each disallowed loss into the next lot's basis, and each subsequent loss sale can be bigger (it carries the prior adjustment). Box 1g adds up every disallowance event during the year — so a trader who churned one falling stock twenty times can show a 1g figure several times their actual drawdown. It's the pattern behind the $800k tax bill on $45k of profit story: mostly optics and timing — unless one of the exceptions below applies.
"But I sold everything!" — the year-end unwind
If you closed the position completely and didn't re-enter for 31+ days (in ANY account), the deferral chain unwinds: the final sale used the accumulated (higher) basis, so earlier disallowances came back as a smaller gain or bigger loss on the last rows. The 1099-B still displays the disallowed amounts in 1g — that's historical record, not a live penalty. Two gotchas keep it from unwinding: re-entering within 30 days before year-end (the December loss defers into January — rule mechanics), and re-entering in an account the selling broker can't see.
What box 1g does NOT include (the real risk)
- Cross-account and cross-broker washes. Brokers net only identical securities within one account. A re-buy at another broker or in your spouse's account never reaches any box 1g — but the IRS counts it, and the adjustment is your job on Form 8949, code W (TurboTax steps).
- IRA absorptions. A re-buy inside your traditional or Roth IRA doesn't just defer the loss — per Rev. Rul. 2008-5 it destroys it permanently, and it appears on no form at all (full explainer).
What to do in February
- Don't panic at the 1g number — most of it is usually deferral accounting.
- Reconcile across ALL your accounts: drop every broker's CSV into our free checker (in your browser, nothing uploaded) and compare its cross-account view against what your 1099-Bs show. The gap between the two IS your Form 8949 to-do list.
- Bring the year-end summary to your CPA — especially if any replacement landed in an IRA.
Frequently asked questions
What does "wash sale loss disallowed" on my 1099-B mean?
Box 1g reports the portion of your losses your broker could not let you deduct because you re-bought substantially identical securities within the 61-day window — in that same account. It is an adjustment, not a penalty: the amount was added to the replacement shares’ basis.
I sold all my shares — why does my 1099-B still show a wash sale?
Usually because a re-buy happened inside the window at some point during the year, deferring a loss into a lot you later sold. If you exited completely and stayed out for 31+ days before year-end, the deferrals generally unwind and the economics net out across rows — check the whole form, not one line.
Is wash sale loss disallowed money I lost forever?
Usually no — it is a timing shift: the disallowed loss moved into the replacement lot’s basis and comes back when you sell that lot cleanly. The exceptions: replacements inside an IRA (permanently lost per Rev. Rul. 2008-5) and cross-account washes your brokers never reported, which you must handle yourself.
Can my 1099-B show gains even though I lost money?
Yes. Repeated re-buys of a falling ticker roll losses forward via basis adjustments; if positions are still open (or washed into an IRA) at year-end, the 1099-B can legitimately show taxable gains in a losing year. This is the mechanism behind the famous $800k-tax-bill-on-$45k-profit Robinhood case.