How do I handle adjusted basis when Form 1099-B looks wrong?

Find the source of the basis before changing the return.

For employer stock, automatic sales, and discounted purchase plans, the broker's basis may not tell the whole story. A supplemental employer-stock statement may show compensation already included in wages, which can affect adjusted basis.

Original example:

• Mira Patel leaves an employer and a few plan shares are sold.
• Form 1099-B shows proceeds and a small cost basis.
• Her year-end stock-plan statement shows wage income connected to those shares.

Mira should not assume the corrected-form checkbox answers the basis question. She should reconcile the broker form, W-2, and stock-plan supplement so she does not double count income or omit gain.