Check the 30-day window, the disallowed loss and the new basis of your replacement shares
Estimates only, not financial advice. What you type stays on your device. Checked against sources on 29 Sept 2026.Enter the dates and amounts of a loss sale and any purchases around it. The calculator finds the 61-day window from 30 days before to 30 days after the sale, matches replacement shares one for one, and shows the disallowed loss, the deductible rest, the new cost basis and when the new shares turn long-term.
Rates and rules read from IRS Publication 550, Investment Income and Expenses (Wash Sales) on 29 Sept 2026; they may have changed since.
Under "The loss sale" enter the "Date you bought the shares you sold", the "Date you sold them" and the "Shares sold".
Enter "Their total cost basis" and "Total sale proceeds" in dollars.
For each repurchase enter the date, "Shares bought", "Total paid" and whether it was "Bought in" a taxable account or an IRA; press "Add a purchase" for more.
Read "Loss you can deduct now" and open "Replacement shares" for the new basis, then press "Share result".
A wash sale happens when you sell a stock or fund at a loss and buy the same or a substantially identical security within 30 days before or after the sale. The IRS then refuses the loss for now. It is not gone: IRS Publication 550 moves the disallowed loss into the cost basis of the replacement shares, and the holding period of the shares you sold carries over to them.
Partial replacement. If you buy back fewer shares than you sold, only that many shares are washed. Publication 550 matches the shares bought with the shares sold, first purchase first. Sell 100 shares at a $1,000 loss and buy back 60, and $600 is disallowed while $400 stays deductible this year. Each replacement purchase takes its share of the disallowed loss by its number of matched shares.
The window counts calendar days. Day 30 after the sale is still inside; day 31 is the first safe day to buy back. Purchases in the 30 days before a sale count too, which is the part people forget when they add to a losing position and then sell the older shares.
Holding period. The replacement shares are treated as held from an earlier date, the purchase date minus the days you held the old shares, so they can turn long-term sooner than their own purchase date suggests. The calculator shows that date.
IRA purchases. Buying the replacement in an IRA or Roth IRA still triggers the rule, but the loss is not added to any basis, so it is lost for good.
What this calculator does not do: decide whether two funds are substantially identical, handle options, short sales or a spouse's account, or read your Form 1099-B. Your broker reports wash sales only within one account and the same CUSIP; the rule applies across all of them. An estimate, not tax advice.
The wash sale rule stops you deducting a loss on a stock or security if you buy the same or a substantially identical one within 30 days before or after the sale. The loss is not lost: IRS Publication 550 adds it to the cost basis of the new shares, so it lowers the gain or raises the loss when you finally sell them.
Wait until the 31st day after the sale. The window runs from 30 days before the sale to 30 days after it, 61 days in all, and a purchase on day 30 still counts. Buying in the 30 days before the sale also counts, so check recent purchases before you sell.
Only the shares you bought back are washed. Publication 550 matches purchases to the shares sold one for one, in the order you bought them. Selling 100 shares at a $1,000 loss and buying back 60 disallows $600 and leaves $400 deductible this year. The $600 goes into the basis of the 60 new shares.
Add the disallowed loss to what you paid for the replacement shares. In the IRS example, 100 shares bought for $1,000 and sold for $750 give a $250 loss; buying 100 again for $800 makes the new basis $1,050. The holding period of the old shares is added to the new ones as well.
Yes. Publication 550 lists buying substantially identical stock for your IRA or Roth IRA as a wash sale. Unlike a purchase in a taxable account, the disallowed loss is not added to any basis, because IRA assets have no basis for this purpose. The loss is gone permanently, which makes this the costliest version of the rule.
No. Brokers report a wash sale on Form 1099-B only when the shares were bought in the same account with the same CUSIP number. Purchases in another account, your spouse's account or an IRA are not reported, but the rule still applies to them, and you report the adjustment yourself on Form 8949 with code W.
Rates and rules change; check the source before you rely on a figure.
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