Wash Sale Rule Calculator

Selling a stock at a loss feels like a clean way to harvest a tax benefit, but the IRS Wash Sale Rule can quietly disallow that capital loss and reshape your adjusted cost basis. This tool maps out whether your repurchase falls into the trap, so your tax reporting reflects what the IRS will actually accept rather than what you hoped to claim.

The trigger is mechanical: sell a security at a loss, then buy substantially identical stock within 30 days before or after the sale, and you land inside a 61-day window that voids the deduction. When that happens, the disallowed loss isn't gone forever. It rolls into the cost basis of the replacement shares, raising that basis by exactly the amount you couldn't deduct.

Many investors track only the exact ticker and miss the wider net the rule casts. Buying a contract or option to buy the same stock inside the window counts too, and so does a purchase by your spouse or by a corporation you control. The rule also reaches your IRA: if the replacement shares go into an IRA or Roth IRA, the loss is disallowed and is not added to any basis, so it is lost rather than deferred. Whether two different funds tracking the same index are substantially identical is a facts-and-circumstances question that IRS Publication 550 does not settle. Treat the position, not the symbol, as what you're really watching.