What the window is

Under the IRS wash sale rule, a loss on selling stock is disallowed for the moment if you buy substantially identical stock or securities within 30 days before or 30 days after the sale. Counting the sale day itself, that makes a window of 61 calendar days. Calendar days, not trading days: weekends and holidays count.

The loss is not gone. It is added to the cost basis of the replacement shares, and the holding period of the shares you sold carries over to them, so the loss comes back into play when you sell the replacement. The wash sale page walks through that with numbers, and cost basis explains what the adjustment does to your records.

What this calculator does not know

It counts dates. It cannot tell you whether two securities are substantially identical, which is a judgment the IRS leaves to the facts, and it cannot see your other accounts. Purchases in any of your accounts can count, including an IRA, and brokers generally only track wash sales within the single account they hold. Automatic dividend reinvestment is a purchase too, so a reinvested dividend inside the window can trigger a partial wash sale on the shares it buys.

Treat the result as a calendar check before you act, and confirm anything that matters with IRS Publication 550 or a tax professional. For the wider tax picture of active trading, see whether you owe tax on trades you never withdrew and choosing tax lots before you sell.

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