Wash Sale Rule Loss Calculator

How to do it

1. 1
   Enter the sale

   Type the shares sold, the basis and sale price per share and the sale date.

2. 2
   Enter the repurchase

   Type the shares bought, the price and the date, even if it was months later.

3. 3
   Check the window

   The result shows the gap in days and whether the 61-day window applies.

4. 4
   Read the loss

   See the disallowed and allowed loss and the estimated tax effect.

5. 5
   Note the new basis

   The adjusted basis per share is what you will use when you sell the new shares.

About this tool

The wash sale rule stops you from claiming a tax loss on a security if you buy the same or a substantially identical one within 30 days before or after the sale. The loss is not gone forever; it is added to the cost basis of the new shares. This calculator takes the sale (shares, basis, price, date) and the repurchase (shares, price, date), checks the 61-day window, works out how much of the loss is disallowed when you bought back only some of the shares, shows the loss you can still claim now, the adjusted basis per new share and the first day you could buy back safely.

Who this is for Investors who sell at a loss to offset gains (tax-loss harvesting), people who use automatic purchase plans and may repurchase without noticing, and anyone who received a 1099-B showing a wash sale adjustment and wants to understand it.

The rule in practice The window is 61 days: 30 days before the sale, the day of the sale and 30 days after. If you buy replacement shares in that window, the loss on the matching number of shares is disallowed for the current year. The disallowed loss is added to the basis of the replacement shares, and the holding period of the old shares is added to the new ones. If you repurchased fewer shares than you sold, only that proportion of the loss is disallowed.

Reading the result The calculator shows the total loss, the gap in days between sale and purchase, whether it is inside the window, the number of shares matched, the disallowed and the allowed loss, the new basis per replacement share and the estimated tax you save on the loss you can claim, using the tax rate you enter. The "safe date" is the day after the 30-day window ends.

Worked example You sell 100 shares with a basis of $50 at $40, a loss of $1,000, and buy 60 shares at $41 fifteen days later. Sixty of the 100 shares are replaced, so $600 of the loss is disallowed and $400 can be claimed. The 60 new shares get a basis of $41 plus $10 (the $600 spread over 60 shares), which is $51 each. If you wait until day 31 to buy back, nothing is disallowed.

Cautions The rule also applies across accounts, including IRAs, and to purchases by a spouse. Options and contracts on the same stock can count as substantially identical. Brokers report wash sales only for identical securities in the same account, so check your own records. This tool is for understanding and not tax advice.

Worked example

Selling 100 shares at a $1,000 loss and buying back 60 shares 15 days later disallows $600, allows $400 and sets the new basis at $51 per share.