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This 1099-B cost-basis column field map outlines every relevant form entry to help U.S. households accurately calculate reportable capital gains and losses. Mismatched or misread cost basis figures are one of the most common triggers for IRS automated underreporter notices, even when filers have no actual unreported tax liability. You will not need specialized tax software to cross-check these entries if you work line by line with your year-end trade confirmations and account statements. This reference from FinanceFortifyHub aligns directly with current IRS Form 1099-B specifications to avoid common entry errors on Form 8949 and Schedule D.
Box 1e entries correspond to core broker-reported cost values for every covered security sale on the form
Box 1e is the baseline cost basis figure brokers are legally required to report for all covered securities, defined by the IRS as equities purchased after 2011, mutual funds and exchange-traded funds purchased after 2012, and debt securities and options purchased after 2014. The value listed here includes the original purchase price of the security plus most purchase-side commissions and fees the broker charged at the time of acquisition, but it does not always reflect post-purchase adjustments that change your final reportable basis. For non-covered securities purchased before the IRS reporting mandates took effect, brokers may leave Box 1e blank, mark it as “not reported,” or list a reference value that is not submitted to the IRS for matching. The below field map outlines every adjacent column that modifies the baseline Box 1e figure, so you can trace each adjustment to its source before entering numbers on your tax return:
1099-B Cost-Basis Column Field Map
| Column Label on 1099-B | Corresponding IRS Box Number | What It Means for Your Cost Basis | Verification Action |
|---|---|---|---|
| Unadjusted cost basis | 1e | Baseline purchase price plus allowed purchase expenses for covered securities | Match to trade confirmation purchase amounts, and add any eligible reinvested dividend or fee amounts not already included |
| Wash sale loss disallowed | 1g | Value of capital loss barred from immediate deduction due to substantially identical repurchases | Confirm the adjustment ties to a trade within the 30-day window before or after the sale, across all accounts you own |
| Accrued market discount | 1f | Taxable interest earned on discounted debt securities held up to the sale date | Adjust basis to reflect amounts you already reported as annual interest income to avoid double taxation |
| Basis reporting category code | 12 | Flag for the IRS indicating if basis is reported, holding period, and applied adjustments | Match the code to the correct Form 8949 section to avoid automated IRS mismatch notices |
| Date acquired / Date sold | 1b / 1c | Timestamps used to calculate holding period and link sales to specific purchase lots | Cross-reference to personal trade logs to confirm the correct lot was matched to each sale |
Wash sale adjustment fields modify listed cost basis to reflect disallowed losses from substantially identical repurchased positions
The value listed in Box 1g, labeled “Wash sale loss disallowed,” adjusts your reported gain or loss to comply with IRS wash sale rules, which bar immediate deduction of capital losses if you purchase a substantially identical security within 30 days before or after the sale date. The disallowed loss amount is not erased permanently; it is added to the cost basis of the newly purchased substantially identical position, which reduces your taxable gain (or increases your deductible loss) when you eventually sell that new position. A common reporting error is double-counting the wash sale adjustment: for most standard broker filings, Box 1e reflects original purchase basis, and Box 1g is the separate disallowed loss reported as a Form 8949 adjustment, not a figure to add or subtract directly from Box 1e. Illustrative example: You purchase 15 shares of a broad market ETF for $450, sell all shares for $300 to realize a $150 loss, then repurchase 15 identical shares of the same ETF 12 days later for $310. The broker will list $450 in Box 1e, $150 in Box 1g, and apply reporting Code W to the transaction. The $150 loss is disallowed on this sale, and your basis in the newly purchased 15 shares becomes $460 ($310 purchase price + $150 disallowed loss). Note that brokers are only required to track wash sales for identical CUSIPs within the same taxable account, so you will need to calculate and report adjustments yourself if the repurchase happened in a different account, such as a spousal joint account or your retirement account.
Accrued market discount columns adjust baseline cost figures for taxable interest earned on sold debt securities held during the year
Box 1f, the accrued market discount field, only applies to debt securities including corporate bonds, Treasury notes and bills, and zero-coupon instruments you purchased on the secondary market for less than their face (par) value. The gap between your discounted purchase price and the security’s par value counts as taxable ordinary interest income as it accrues over the life of the bond, rather than being treated entirely as capital gain when you sell or redeem the security. If you did not elect to report accrued market discount as ordinary income each year you held the security, you must reduce your baseline Box 1e cost basis by the amount listed in Box 1f when calculating your capital gain or loss, and report that accrued discount amount as interest income on your return. If you did make the annual election to report accrued discount each year, you will not need to adjust your basis, as you have already paid tax on that income in prior filing years. Illustrative example: You purchase a 10-year $1,000 par corporate bond on the secondary market for $900, generating $100 of total market discount that accrues at $10 per year. You hold the bond for three years, then sell it for $950. The broker will list $900 in Box 1e, $30 in Box 1f for three years of accrued discount. If you did not make the annual accrual election, your adjusted basis for capital gain calculation is $870, resulting in $80 of long-term capital gain and $30 of ordinary interest income from the sale. This adjustment does not apply to tax-exempt municipal bonds for federal filing, though state rules may vary for in-state and out-of-state municipal holdings.
Basis reporting codes signal if listed cost figures reflect short-term, long-term, or adjusted values for IRS matching
The short alphanumeric codes printed in Box 12 of the 1099-B are not internal broker reference numbers — they tell the IRS exactly what type of transaction is being reported, and what level of basis verification the broker completed for the line item. The most common codes are: Code A for short-term covered transactions with reported basis, Code B for short-term non-covered transactions where basis is not submitted to the IRS, Code D for long-term covered transactions with reported basis, Code E for long-term non-covered transactions without IRS-submitted basis, and Code W for transactions with an applied wash sale adjustment. If you enter a cost basis figure under the wrong code category, the IRS automated matching system will flag the entry as a mismatch even if your math is accurate, as the system expects values aligned to specific reporting sections. For non-covered transactions marked with Codes B or E, the IRS will not have a broker-reported basis number on file to cross-check against your return, so you are responsible for retaining records of purchase price, corporate action adjustments, and fees to support the basis you claim. If you see a code you do not recognize, cross-reference it to the IRS 1099-B instructions before entering the transaction on your return, rather than assuming it maps to a standard short- or long-term gain category.
Transaction date cross-references let you match listed cost-basis figures to personal trade logs to catch reporting mismatches
The date acquired (Box 1b) and date sold (Box 1c) columns are not only used to determine if a gain or loss qualifies for short-term (held one year or less) or long-term (held more than one year) tax rates; they act as unique identifiers to line up every reported sale against your own personal trade records, including trade confirmations, account transfer statements, and records of corporate actions like stock splits, spinoffs, or reverse mergers that adjust original basis. Brokers occasionally make basis reporting errors, particularly for assets transferred between firms, subject to corporate actions while held, or sold with specific tax lot selection that misprocessed in their system. Common mismatches include missing basis adjustments for account transfer fees, incorrect lot matching for partial sales of multi-lot positions, and wash sale adjustments applied to transactions the broker cannot track across accounts. If you identify a mismatch between your records and the 1099-B figure, first reach out to your broker to request a corrected 1099-B if the error stems from their record-keeping. If a corrected form is not available, you can report the accurate basis on Form 8949 with the appropriate adjustment code, and attach a short statement explaining the difference if required. This material is for educational purposes only; if you have complex transactions involving options, debt securities, or cross-account wash sales, consult a licensed tax professional to confirm your reporting is accurate, as no guidance on this page can substitute for personalized tax advice.
Your next step is to pull a copy of your full-year trade confirmation log from your brokerage account, and line up each entry on your 1099-B to the matching trade using the sale and acquisition dates before you enter any cost basis figures on your tax return.
Written by the FinanceFortifyHub editors.