How do I adjust the cost basis for my trades that incurred a wash sale on my 1099.

Do I total all of the wash sales and add to the cost basis of the last trade? see below image

wash sale picture

1 Answer 1


Your disallowed losses should be added to the cost basis of the replacement shares, not the last trade.

You sold, for example, 1,350,000 units on 7/26/22 and presumably bought them again either before or after the sale. These repurchased units are the replacement shares, and the disallowed loss adds to their cost bases.

Whether the last trade is from any of the replacement shares for any of the disallowed losses - we don't know. But it may be that you'll have both gains and disallowed losses for the same security, depending on your trade history.

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