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What is the supplemental stock plan lot detail report?

Supplemental lot detail reports often hold the vest price you need when 1099-B basis is wrong.

Rates and rules change. Content is reviewed for tax year 2026. Check the last-reviewed date and methodology on each page, then confirm against IRS or state guidance before you file.

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In plain terms

Brokerages that administer equity plans often provide a supplemental report alongside the . It usually lists each lot's and price, the information the may leave blank. It is often the cleanest place to find the numbers you need to adjust basis.

How the tax works

The official may report $0 or missing basis for shares, especially noncovered lots.

Plan administrators know the details, so they include them in a separate supplemental statement.

That supplemental detail is for your records and return preparation; it is generally not filed with the IRS by you.

Matching each sold lot to its price is how you compute the correct basis adjustment.

What to check on your end

  • Whether your broker provides a supplemental or 'stock plan' statement.
  • and per share for each lot.
  • How sold lots map to the lots listed.
  • That the supplemental basis matches your own confirmations.
  • Short-term vs long-term classification for each lot.

Common mistake

Filing from the alone and ignoring the supplemental report. The may not tell the whole story, the supplemental detail is often where the real basis lives.

Example scenario (hypothetical)

Illustration only, not your tax situation.

Example: Casey's shows $0 basis on a sale of 60 shares. The supplemental report shows those 60 shares vested at $48. Casey uses $48 per share ($2,880) as the adjusted basis when reporting the sale.

When a CPA is worth it

  • The supplemental report and your own records disagree.
  • Lots were sold in pieces and basis tracking is unclear.
  • You cannot locate a supplemental statement and the shows $0 basis.
  • You have wash-sale concerns across lots.

Sources and notes

Primary tax claims on this page are supported by the official and secondary sources below. Broker and software links describe reporting mechanics — confirm rules against IRS or state guidance.

How RSU vest wages and share sales appear on W-2, 1099-B, and Form 8949.

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VestingTax.com is not a CPA firm or tax preparer. Grants, employers, and states all differ. Use the cited IRS and state sources above, your own documents, and a qualified tax professional before you make decisions from this guide.

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