What box on Form 3922 should I used for adjusted cost basis for ESPP sales?

To figure out the adjusted cost basis for your ESPP (Employee Stock Purchase Plan) sales using Form 3922, you'll need to look at these boxes:

1. Box 3: This shows the fair market value (FMV) of the stock on the date the option was granted.
2. Box 4: This shows the FMV of the stock on the date the option was exercised.
3. Box 5: This shows the price paid per share.

To calculate the adjusted cost basis, you typically use the FMV on the date of exercise (Box 4) minus the price paid per share (Box 5). This adjusted cost basis is then used to determine your gain or loss when you sell the stock

You can find the instructions for Form 3922 on the IRS website. Here is the link: Instructions for Forms 3921 and 3922