I’m asking about U.S. federal taxes in a regular taxable brokerage account.
Suppose I repeatedly sell and repurchase the same stock every five days, creating a chain of wash sales:
I start trading one share in January.
In June, I add a second share. From then on, I buy and sell both shares together in the same transactions.
After accounting for previous wash-sale basis adjustments, the two shares carry different accumulated losses.
My final purchase of both shares is November 20, and I sell both together on November 25, fully exiting the position. Assume the adjusted losses on that final sale are $10,000 for one share and $1,000 for the other.
On December 15, I accidentally buy one share of the same stock and hold it through year-end. Assume there are no other relevant purchases, including in other accounts.
My understanding is that this replacement share causes a wash sale for only one of the two shares sold. How do I determine which loss is deferred—the $10,000 loss or the $1,000 loss?
I’ve read that Treasury Regulation §1.1091-1(b) uses original acquisition order when the order of same-day sales cannot be determined. But here, both final shares were acquired together on November 20 and sold together on November 25.
Does the matching rule look back to the January versus June origins of the wash-sale chains, use the latest actual purchase date, or apply some other tie-breaking rule? Is there any permitted taxpayer choice?
I’d especially appreciate a citation or guidance addressing this exact situation.