Picture this: you open your 1099-B in March and see a five-figure “gain” on shares you sold the same week they vested — or worse, on shares your broker sold automatically for taxes. The cost basis column says $0.00. Tax forums fill with this exact panic every single year, and the punchline is brutal: people who don’t catch it genuinely pay tax twice on the same income. The fix takes ten minutes once you know where to look.
Why brokers report $0 — on purpose
This is not a glitch. Under the cost-basis reporting rules brokers operate under, the “basis” they must report for equity-compensation shares is essentially the cash you paid for them. For RSUs that number really is zero — the value reached you through payroll, not through a purchase. Years ago practices varied; brokers have since converged on reporting $0 (or only a partial figure) in the official Box 1e and disclosing the true number elsewhere. The IRS knows this and expects you to make the adjustment on your return.
The result is a form that is technically compliant and practically misleading. Your W-2 already carried the vest-date value into taxed income. If the sale is then reported with a $0 basis, the entire sale proceeds get taxed a second time as a capital gain.
What your real basis is
For RSUs the rule is one line long: basis = fair market value per share on the vesting date × shares. It is the same dollar amount that hit your W-2. If 250 shares vested at $42.10, your basis is $10,525 — for those shares, whether you sell them next day or in five years. Each vest lot has its own basis tied to its own vest date, which matters when you sell shares from several lots at once.
How much the mistake costs
The same sale, filed two ways
Dev sells 300 vested shares at $70 ($21,000 proceeds). They vested at $65, so his true basis is $19,500 and his real short-term gain is $1,500.
Filed correctly: at a 35% marginal rate, tax on the sale ≈ $525.
Filed with the $0 basis: the return shows a $21,000 gain. Tax ≈ $7,350. Dev has overpaid by $6,825 — on top of the income tax he already paid on the $19,500 at vest. Multiply by quarterly vests over several years and this single clerical habit becomes one of the more expensive recurring errors in personal finance. Wealth managers who review executives’ past returns report finding it constantly, including on returns prepared by professionals.
Where to find the correct number
- The supplemental statement. Fidelity, Schwab, E*TRADE/Morgan Stanley and others attach “supplemental information” pages to the 1099-B showing an adjusted cost basis per lot. This is the number you want, and it is usually the only place it appears.
- Vest confirmations. Your equity portal’s release/confirmation records show shares vested and the FMV used — multiply and you have basis from first principles.
- Your W-2 and pay stubs. The vest income in Box 14 or the year-end stub should reconcile to the sum of (shares vested × vest price) across the year. If it doesn’t, something else is wrong — pull the thread.
How to fix it on your return
The IRS-prescribed mechanism lives on Form 8949:
- Report the sale as it appears on the 1099-B (so the IRS computer can match it).
- Enter adjustment code B in column (f) — the code for “basis shown on 1099-B is incorrect.”
- Put the correction amount in column (g), reducing the gain to its true size.
Every mainstream tax program supports this: when you import or enter the 1099-B, look for a prompt like “the basis on my statement is incorrect or missing,” then supply the adjusted basis from the supplement. The software produces the code-B entry for you. Do this for every RSU lot sold in the year — including the lots sold automatically for tax withholding, which trip people up because they never clicked “sell.”
The 60-second audit before you file: open Form 8949, find each RSU sale, and compare column (e) against the supplemental statement’s adjusted basis. If they match (directly or via a column (g) adjustment), you are safe. If column (e) is $0 and column (g) is blank, stop and fix it. This check catches the error whether you self-prepare or pay someone.
Already filed it wrong? Amend.
If you discover a past year where RSU or ESPP sales went through with a $0 basis, file Form 1040-X with a corrected Form 8949 and Schedule D. The general window is three years from the date you filed the original return (or two years from when you paid the tax, whichever is later) — so a mistake found today is typically recoverable for the last three filing seasons. State amended returns follow their own rules but usually mirror the federal correction. The refund is your own money; the form exists precisely for this.
About those IRS letters
Two opposite fears circulate online. One says “changing the broker’s number will get me audited” — no: the code-B adjustment is the official channel, and keeping the supplemental statement in your records answers any question before it is asked. The other fear arrives as a real letter: a CP2000 notice proposing extra tax because a sale on a 1099-B never appeared on the return at all. That is the more common failure, especially with sell-to-cover lots. The cure for both is the same discipline: report every lot, adjust every basis, keep the supplement.
The annual five-line checklist
- Download the 1099-B and its supplemental pages from your broker.
- List every RSU lot sold this year, including automatic tax-withholding sales.
- For each lot, confirm basis = vest-date FMV × shares (the supplement should already say this).
- Enter or import sales, applying the adjusted basis (code B) wherever the official box is $0 or understated.
- Reconcile total vest income against your W-2 before you press file.
Key takeaways
- Your true RSU cost basis is the share price on the vesting date — the same value that was already taxed as W-2 income.
- Brokers are generally required to report only what you paid in cash for shares, which for RSUs is $0, so 1099-B forms standardly show a $0 or understated basis.
- The corrected basis usually lives in a supplemental statement attached to your 1099-B, not in the official boxes.
- You fix it on Form 8949 with adjustment code B — you do not overwrite the broker's number and hope.
- Past mistakes can be repaired: amended returns (Form 1040-X) are generally available for roughly three years after filing.
Frequently asked questions
Why does my 1099-B show $0 basis for RSUs I paid tax on?
Broker reporting rules only require the cash you paid for shares to be reported as basis. You paid nothing in cash for RSUs — the value was delivered through payroll — so many brokers report $0 and disclose the true vest-date basis only in a supplemental statement.
Will correcting the basis trigger an IRS notice?
Reporting a different basis is exactly what Form 8949's adjustment columns exist for. Using code B with the correct adjustment is the IRS-prescribed method. What more often triggers CP2000 notices is omitting the sale entirely or sloppy math, not a documented correction.
I already filed with a $0 basis. Is the money gone?
Usually not. You can amend with Form 1040-X, generally within three years of the original filing date (or two years from paying the tax, if later), recover the overpaid tax, and correct the record.
Does this apply to ESPP shares too?
Yes, with an extra twist: ESPP basis also omits the taxed discount. The mechanics differ slightly — see our ESPP guide — but the supplemental-statement habit protects you in both cases.
Educational disclaimer: This guide is general information, not financial, investment, tax or legal advice. Figures refer to the tax years stated and change over time; rules differ by jurisdiction and personal circumstances. Verify current figures with the IRS / HMRC and consult a qualified professional before acting. See our full disclaimer.