Wash Sale Disallowed Loss Calculator
See how much of a stock loss the wash-sale rule disallows when you rebuy within 30 days — and how much loss you can still deduct.
How it works
Matched shares = min(rebought, sold) · Disallowed loss = total loss × (matched ÷ sold) · Deductible = loss − disallowed · Disallowed loss is added to the replacement shares’ cost basis
The wash-sale rule disallows a loss when you buy substantially identical stock within 30 days before or after the sale. Only the portion matched by replacement shares is disallowed — if you rebuy fewer shares than you sold, the rest of the loss still counts. Critically, the disallowed loss is not lost forever: it is added to the cost basis of the replacement shares, so you recover it when you eventually sell those without triggering another wash sale.
Worked example
You sell 100 shares for a $2,000 loss, then buy 60 replacement shares inside the 30-day window. Sixty of the hundred are matched, so 2,000 × 60/100 = $1,200 is disallowed and $800 stays deductible now. The $1,200 is added to the 60 new shares’ basis ($20 each), preserving it for later.
Frequently asked questions
What triggers the wash-sale rule?
Selling a security at a loss and buying the same or a substantially identical security within 30 days before or after the sale — a 61-day window in total. It also applies if the purchase is in your IRA or your spouse’s account.
Do I lose the disallowed loss permanently?
No. The disallowed amount is added to the cost basis of the replacement shares (and their holding period extends). You claim it when you sell those shares in a non-wash transaction, so the benefit is deferred, not destroyed.
Does the wash-sale rule apply to crypto?
Under current U.S. law the rule applies to stocks and securities, not to cryptocurrency, so crypto losses can generally be harvested without a 30-day wait — though proposals to extend the rule to crypto appear regularly.
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Educational estimate using 2024 U.S. federal figures — ignores state tax, credits, phase-outs and your full situation. Not tax advice; confirm with a professional or the IRS.