Form 8949 Box A vs Box B vs Box C: Short-Term 1099-B Reporting Explained

Your broker handed you a consolidated 1099-B that says "Short-Term — Basis Reported to IRS" at the top of one page and "Short-Term — Basis NOT Reported to IRS" at the top of another. Your tax software is asking you to assign every transaction to Box A, Box B, or Box C on Form 8949. Nothing in any of those headers tells you which is which, and the IRS instructions explain the difference using the word "covered" 38 times without ever defining it in plain English.

This is one of the most confusing parts of the entire 1099-B reporting flow, and getting the box wrong creates a paper trail mismatch that triggers IRS notices months later. The good news: the rules are simple once you see them laid out side by side. This guide does exactly that — what each box means, how to decide which one to use, what your broker's 1099-B pages actually mean, and the half-dozen edge cases that cause most of the errors.

What Each Short-Term Box Means

Form 8949 splits short-term transactions (held one year or less) into three boxes based on two questions: did your broker issue a 1099-B, and did they report the cost basis to the IRS?

Box	1099-B issued?	Cost basis reported to IRS?	When to use
A	Yes	Yes	Most modern stock sales
B	Yes	No	Older lots, certain ETFs, transferred shares
C	No	No	Private sales, peer-to-peer, foreign brokers

The single most important distinction is between Box A and Box B. Both come from a 1099-B you received. The difference is whether the broker also told the IRS your cost basis. Box A = they told the IRS. Box B = they sent you the basis on the 1099-B but didn't transmit it to the IRS.

Box C is rarer for typical investors. It's for transactions where you sold a capital asset but no 1099-B was issued at all — a private stock sale, certain wash trades, foreign brokerage transactions, sales of collectibles outside of a regular broker, etc.

The "Covered Security" Concept

The legal basis for these boxes is the IRS "covered security" rule. A covered security is one the broker is required to report cost basis on. Whether a security counts as "covered" depends on when you acquired it:

• Stocks acquired on or after January 1, 2011 — covered
• Mutual funds and ETFs acquired on or after January 1, 2012 — covered
• Bonds and options acquired on or after January 1, 2014 — covered
• Certain less complex bonds acquired on or after January 1, 2016 — covered

If you bought before those dates, the security is "noncovered" — your broker may have the basis in their records, but they're not required to send it to the IRS. Even if the basis appears on your 1099-B, it lands in Box B (or its long-term equivalent, Box E) because the IRS doesn't have it.

This matters for one practical reason: when basis is reported (Box A), the IRS auto-reconciles your reported gain against the broker's number. When basis is not reported (Box B or C), the IRS only sees the proceeds, so the reconciliation is less automated — which means your reporting carries more weight.

How Your Broker's 1099-B Maps to the Boxes

Every consolidated 1099-B from a US broker organizes short-term transactions into sections that map directly to Form 8949 boxes. Section headers vary slightly by broker, but the underlying classification is identical.

Broker section header	Form 8949 box
"Short-Term — Covered" / "Basis Reported to IRS"	A
"Short-Term — Noncovered" / "Basis NOT Reported to IRS"	B
Nothing (no 1099-B issued at all)	C

Specific phrasings you'll see:

• Schwab / Fidelity / Vanguard / Merrill — explicitly label "Short-Term Transactions for Covered Tax Lots" (Box A) and "Short-Term Transactions for Noncovered Tax Lots" (Box B)
• E*TRADE — uses "Short-Term — Basis Reported" and "Short-Term — Basis Not Reported"
• Robinhood — labels them "Short-Term — Box A" and "Short-Term — Box B" outright; least ambiguous
• TD Ameritrade / Charles Schwab integration — same as Schwab format after the merger
• IBKR / Webull / TastyTrade — usually label by box letter directly

If your 1099-B's section labels don't include the words "covered," "basis reported," or the box letter, look for a section showing positions where the cost basis columns are blank or marked "N/A" — those are your Box B transactions.

Box A: The Common Case

Box A covers the vast majority of stock and ETF transactions for anyone who's been investing since 2012-ish on a US broker. If you bought a share of AAPL on Robinhood in 2023 and sold it three months later, it's Box A. The broker had the basis (they sold you the shares, so they know what you paid), they tracked it, they reported it on the 1099-B, and they transmitted it to the IRS.

For Box A transactions, the IRS expects your Form 8949 gain/loss to exactly match the broker's number. Any deviation has to be explained with an adjustment code. The common reason to deviate is a wash sale or other adjustment code, which lets you modify the basis or gain/loss while still reporting it under Box A.

If you accept the broker's numbers without modification (no wash sales, no corrections), you can even skip Form 8949 entirely for these transactions and report them as summary totals directly on Schedule D — see the Form 8949 from 1099-B guide for that shortcut path.

Box B: The Cost Basis Is on You

Box B is where things get interesting. The broker sent you a 1099-B with cost basis on it, but didn't tell the IRS. Common reasons a transaction lands in Box B:

1. You transferred shares from another broker and the basis didn't transmit with them. The receiving broker shows it on your 1099-B but flags it as noncovered.
2. You bought the shares before the covered-security cutoff for that asset class (pre-2011 for stocks, pre-2012 for funds).
3. Certain ETFs and special situations — particularly ETFs that hold physical commodities (GLD, SLV) or have a Section 1256 component.
4. DRIP reinvestments from before the cutoff — even though the underlying position is covered, those older lots aren't.

For Box B transactions, you (the taxpayer) are the source of truth on cost basis. The IRS doesn't have a number to compare against, so your reported figure stands — but it also means you carry the audit risk if your number is wrong.

The most common Box B trap is incorrect basis that your broker pulled from imperfect transfer data. If you moved shares from Schwab to Fidelity in 2019, Fidelity may show $0 cost basis on the 1099-B because Schwab didn't send the historical lot data. The Box B treatment is correct (basis not IRS-reported), but the $0 basis is wrong — see 1099-B noncovered securities missing cost basis for the workflow to correct it.

Box C: No 1099-B at All

Box C is the smallest bucket. It exists for short-term capital gains/losses on transactions where no 1099-B was issued. Examples:

• Private stock sales — selling shares of a non-public company directly to another investor
• Peer-to-peer sales of collectibles, crypto (pre-2026 rules), or other capital assets
• Foreign brokerages that don't issue US 1099-Bs but where you owe US tax on the sale
• Lost or never-received 1099-B where you have the transaction data from your own records
• Wash sale tracking adjustments where you're reporting a position the broker didn't report

The IRS has no third-party confirmation for Box C transactions. You report what you sold, when, for how much, and what you paid — and that's what becomes the IRS's record.

If you're using Box C because the 1099-B never arrived (lost in mail, broker glitch), don't wait. Reconstruct the data from your account statements, file it as Box C, and request a duplicate 1099-B for your records. Filing late or filing without it both create more problems than Box C reporting does.

Decision Flow: Picking the Right Box

For each short-term transaction, ask three questions in order:

1. Did I receive a 1099-B that includes this transaction?
   • No → Box C
   • Yes → continue
2. Does the 1099-B show cost basis for this transaction? (Look at the cost basis column — is there a dollar amount, or is it blank/marked noncovered?)
   • Blank or noncovered → Box B
   • Has a dollar amount → continue
3. Is the section header "covered" / "basis reported to IRS"?
   • Yes → Box A
   • No → Box B

In practice, the broker's section headers do the work for you 95% of the time. Trust the section the transaction is listed under, and use the decision flow only when the 1099-B is ambiguous or you have transactions outside the 1099-B.

What Changes Between the Boxes on Form 8949

The boxes are not just a label — they determine how Form 8949 itself fills out:

Column	Box A	Box B	Box C
(a) Description	Required	Required	Required
(b) Date acquired	Required	Required	Required
(c) Date sold	Required	Required	Required
(d) Proceeds	Required (matches 1099-B)	Required (matches 1099-B)	Required (from your records)
(e) Cost basis	Required (matches 1099-B)	Required (from your records)	Required (from your records)
(f) Code	Only if adjusting	Only if adjusting	Only if adjusting
(g) Adjustment	Only if code present	Only if code present	Only if code present
(h) Gain/loss	Calculated	Calculated	Calculated

The functional difference: in Box A, the IRS expects columns (d) and (e) to match what the broker sent them. In Box B and Box C, they don't have a comparison and rely on your numbers.

Practically, this means Box A transactions with no adjustments are the simplest to report — many tax programs let you summarize them on a single row. Box B and Box C transactions, lacking IRS basis confirmation, almost always need to be listed individually so the IRS can see your math.

Long-Term Equivalents

The long-term side (positions held more than one year) uses the exact same structure with different box letters:

• Box D = long-term, basis reported (mirror of Box A)
• Box E = long-term, basis NOT reported (mirror of Box B)
• Box F = long-term, no 1099-B (mirror of Box C)

Everything in this guide applies identically — substitute the long-term box for the short-term equivalent. The covered-security rules and reporting requirements are identical; only the holding period changes.

Common Mistakes

• Lumping Box A and Box B together. Common when running an Excel-based import. Each box has its own Form 8949 page in the IRS's structure — mixing them on one page is technically a filing error.
• Using Box A for transferred shares. If the basis came in from a transfer with no covered-security history, it's Box B regardless of what the broker's display says.
• Skipping Box B because basis is missing. $0 basis is not a reason to skip reporting — fix the basis, then report. The IRS will assume zero basis = 100% gain if you ignore it.
• Treating short-term and long-term identically. A position held 365 days is short-term; 366 is long-term. Verify holding period before assigning boxes.
• Using Box C for transactions that should have a 1099-B. If your broker should have issued one but didn't, contact them first — getting a corrected 1099-B is cleaner than Box C reporting.

FAQ

My 1099-B has only one section labeled "Short-Term." How do I tell A from B?

Look at the cost basis column on the transaction. If every row has a dollar amount in the basis column AND the section header includes "covered" or "basis reported," it's Box A. If the basis column is mixed or the header doesn't say "covered," check each row individually — covered lots have basis amounts, noncovered lots don't.

Can I have the same security in both Box A and Box B?

Yes. If you bought AAPL in 2010 (noncovered) and again in 2020 (covered), and sold both lots in 2026, the older lot is Box B and the newer is Box A. They get reported on separate rows.

What if my broker says basis is reported but my records say it's wrong?

You can still use Box A and add an adjustment with code B (incorrect basis). The IRS allows corrections within Box A reporting — see the form 8949 codes reference for which codes to use.

Are crypto sales Box A, B, or C?

Pre-2026 rules: usually Box C (no 1099-B from most exchanges). Starting in 2026 with the new 1099-DA reporting, crypto sales from compliant exchanges will move to Box A or B depending on the exchange's tracking.

Do options trades go in Box A?

Options acquired on or after January 1, 2014 are covered securities, so yes — most options trades on US brokers go in Box A. Older options or those acquired through certain restricted scenarios may be Box B.

Does it matter if I get the box wrong?

Yes. The IRS uses the box assignment to decide whether to auto-reconcile against the broker's data. Reporting a Box A transaction as Box B may slip past initial review but creates exposure if audited. Reporting Box B as Box A and the basis doesn't match the broker's record (because they didn't report one) can trigger a CP2000 notice asking for the basis source.

Where do these go on Schedule D?

Boxes A through C aggregate into Schedule D Line 1 (Box A summary on Line 1a, Box A detail on Line 1b, Box B detail on Line 2, Box C detail on Line 3). Long-term boxes D through F do the equivalent on Lines 8a, 8b, 9, and 10.

Bottom Line

The Box A / B / C decision on Form 8949 comes down to two questions: did you get a 1099-B, and did the broker report cost basis to the IRS. Box A means yes to both — the easiest, most automated case. Box B means yes to the first, no to the second — you supply the basis. Box C means no to both — you're the only source of record.

For most modern investors with a US brokerage account opened after 2012, almost everything is Box A. Box B shows up around transferred shares, older holdings, and certain ETFs. Box C is for private sales, foreign brokers, and edge cases. Trust your broker's section headers, verify the basis column when in doubt, and never use $0 basis when the real number is reachable from account statements.

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