Form 8949 is where you list capital-asset sales that feed Schedule D. When your broker’s Form 1099-B is incomplete, wrong on basis, or missing a wash-sale you know about, you usually enter a code in column (f) and a dollar adjustment in column (g) so the gain or loss matches reality. Broker starting point: 1099-B basis adjustment basics. Wash-sale mechanics: Wash sale rule basics. Account context: Taxable brokerage account basics. Filing orientation: Filing taxes for beginners.
What the adjustment columns are for
| Situation | Typical 8949 code pattern (confirm current IRS instructions) | What column (g) usually does |
|---|---|---|
| Wash sale disallowed loss | Code W (and related reporting per instructions) | Reduces the deductible loss; disallowed amount often increases replacement-share basis |
| Basis on 1099-B is wrong / incomplete | Codes such as B (basis incorrect) when the form showed basis | Corrects gain/loss to your documented cost basis |
| Type of gain/loss shown is wrong | Codes such as T when short-term vs long-term was mislabeled | Moves the character without inventing proceeds |
| 1099-B said basis was reported to IRS but it is still wrong | Combinations that flag IRS-reported basis errors (per current instructions) | Aligns your return with lot records while documenting the mismatch |
| Multiple issues on one line | Multiple codes as the Form 8949 instructions allow | Net adjustment that produces the correct gain/loss |
Exact letter codes and when you must check boxes for “basis reported to the IRS” change with the year’s Form 8949 instructions. Treat the table as a map of problems, then open the current IRS PDF—do not file from blog memory alone.
Wash sales on Form 8949
When a wash sale disallows a loss, Form 8949 is often where you show the disallowance if the broker missed it (common when the repurchase sits in another login, a spouse’s account, or an IRA). Inside one broker, Fidelity, Schwab, Vanguard, or E*TRADE may already adjust the 1099-B; across brokers, you still own the Form 8949 line. Lot choice matters when you sell: Tax lot identification basics.
Worked example: code W after a cross-broker repurchase
Casey sells 50 shares of ETF ABC in a Fidelity taxable account for a $800 loss on March 10. On March 22 Casey buys the same ETF in a Schwab taxable account. Fidelity’s 1099-B shows an $800 loss with no wash-sale flag (it never saw Schwab). At filing, Casey enters the sale on Form 8949 with the wash-sale adjustment code and a column (g) adjustment that zeros the current-year loss, then increases basis of the Schwab lot by $800. Skipping the code understates taxable income later when the Schwab shares sell—or double-counts the loss if Casey also claims $800 now. Cross-account traps: Wash sales across accounts.
Basis corrections and 1099-B mismatches
Transferred lots, old ESPP/RSU releases, and “0 basis” lines are classic Form 8949 adjustment territory. Reconstruct cost from trade confirms and prior 1099-Bs before you invent a number. If the 1099-B already sent a basis figure to the IRS that you believe is wrong, the instructions usually require both the correct basis and the codes that tell the IRS you disagree—keep worksheets with the return PDF.
Covered vs noncovered lots still matter: covered securities often already have basis reported; noncovered lots frequently need your own basis entry even when proceeds alone appeared on the 1099-B (1099-B basis adjustment basics).
Practical habits
- Export the full 1099-B detail CSV from every broker—not just the summary PDF.
- Reconcile wash-sale candidates across all household taxable accounts you control.
- Match each Form 8949 line to a lot ID (FIFO vs specific ID) before you e-file.
- Keep a one-page worksheet listing code, adjustment amount, and why for every adjusted line.
- Re-check corrected 1099-Bs (common through February–March) before you lock the return.
Checklist
- Open current-year Form 8949 instructions before you pick codes from memory.
- Separate covered and noncovered sales the way the 1099-B parts them.
- Apply wash-sale adjustments when any substantially identical repurchase sits inside the window—even at another broker.
- Correct wrong or missing basis with documentation, not guesses.
- Confirm short-term vs long-term character matches holding period.
- Archive Form 8949 worksheets with the filed return PDF.
Portfolio framing when you are still building the taxable sleeve: Investing basics for beginners.
When the 1099-B is covered vs noncovered (broker reporting cutoffs): Broker cost basis reporting cutoff basics.
Educational only. Not tax, legal, or investment advice. Form 8949 codes and 1099-B reporting rules are technical and year-specific; verify with current IRS Form 8949 / Schedule D instructions and a qualified tax professional.