Form 8949 Code B: Incorrect Basis in Column (g) (2025)

Updated October 17, 2026. Quick answer: Code B goes in column (f) of Form 8949 when the basis on your Form 1099-B or Form 1099-DA is incorrect. What you put in columns (e) and (g) depends on whether the basis was reported to the IRS. If it was not, you enter the correct basis in column (e) and zero in column (g). If it was, you enter the reported basis in column (e) and correct it with an adjustment in column (g).

When code B applies

The code B row in the column (f) table reads “You received a Form 1099-B or Form 1099-DA (or substitute statement) and the basis shown in box 1e on Form 1099-B or box 1g on Form 1099-DA is incorrect”. The instructions explain the purpose of column (f) in general: “In order to explain any adjustment to gain (or loss) in column (g), enter the appropriate code(s) in column (f).” Most rows need none of this. As the instructions put it, “For most transactions, you don’t need to complete columns (f) and (g) and can leave them blank.”

The basis boxes on the statements are covered on Form 1099-B boxes 1d and 1e and Form 1099-DA box 1g.

The Schedule D instructions explain what basis is and why your own records matter when a statement is wrong: “Basis is the amount of your investment in property for tax purposes.” “The basis of property you buy is usually its cost.” “You must keep accurate records that show the basis and, if applicable, adjusted basis of your property.”

What to enter in column (g) when the basis was not reported to the IRS

This case is for a box B, box H, box E or box K row. The instructions say “If this transaction is reported on Part I with box B or box H checked at the top or if this transaction is reported on Part II with box E or box K checked at the top, enter the correct basis in column (e), and enter -0- in column (g).”

The worksheet for basis adjustments says the same thing from its own starting point: “If the basis wasn’t reported to the IRS, enter the correct basis in column (e) and enter -0- in column (g) (unless you must make an adjustment for some other reason).” That sentence also says you do not need to complete the worksheet in this case. Which box applies to your sale is explained on the Form 8949 boxes A to L page.

What to enter in column (g) when the basis was reported to the IRS

This case is for a box A, box G, box D or box J row. The instructions say “If this transaction is reported on Part I with box A or box G checked at the top or if this transaction is reported on Part II with box D or box J checked at the top, enter the basis shown on Form 1099-B or Form 1099-DA (or substitute statement) in column (e), even though that basis is incorrect.” “Correct the error by entering an adjustment in column (g).”

To find the adjustment, the instructions send you to a worksheet: “To figure the adjustment needed, see the Worksheet for Basis Adjustments in Column (g), later.” The Worksheet for Basis Adjustments in Column (g) is a short worksheet in the instructions that starts from the basis shown on the statement and the correct basis. This page does not reproduce its lines. Follow the worksheet printed in your own copy of the instructions, and enter the result in column (g) as it directs.

How column (h) is figured

Column (h) is the last step. The instructions say “First, subtract the cost or other basis in column (e) from the proceeds (sales price) in column (d). Then take into account any adjustments in column (g).” For the adjustment rules the instructions add “Enter negative amounts in parentheses.”

The instructions work a basis example, which is worth reading in full in the instructions. It starts: “You sold stock for $1,000.” “Your correct basis for the stock is $100, but you receive a Form 1099-B or Form 1099-DA that shows your basis is $900 and shows your broker reported that basis to the IRS.” The instructions finish it this way: “Also, enter $800 in column (g) of Part I with box A or box G checked at the top.” “Your gain is $900 ($100 + $800).” “Enter $900 in column (h).”

Combining code B with other codes

Some rows need more than one code. The instructions say “If more than one code applies, enter all the codes that apply in alphabetical order” and “Don’t separate the codes by a space or comma.” On the net amount: “If you entered more than one code in column (f) on the same row, enter the net adjustment in column (g).”

If the same sale also had a wash sale loss, code W is the other letter. See Form 8949 code W for that entry, and the wash sale rule for the rule itself.

Where it goes next

Column (h) gain or loss from each row flows to Schedule D through the part totals. The instructions say “Include on your Schedule D the totals from all your Parts I and II.” More on that side is on the Schedule D page and the Form 8949 instructions page.

Edition and line numbers

This page reads the 2025 Form 8949 and its 2025 instructions, along with the Publication 550 edition for 2025 returns where cited, the current files irs.gov served on 2026-10-17, for the tax year 2025 return filed in 2026. Check the tax year printed on the form you are filling in and use the column letters and codes on that year’s form, because a different year’s form can letter its columns or word its codes differently.

Common mistakes

Entering a corrected basis when the broker reported the basis to the IRS. For the box A, G, D and J rows, the instructions say “enter the basis shown on Form 1099-B or Form 1099-DA (or substitute statement) in column (e), even though that basis is incorrect.” The correction belongs in column (g).
Leaving a number in column (g) when the basis was not reported. For the box B, H, E and K rows, the instructions say to “enter the correct basis in column (e), and enter -0- in column (g).”
Putting a comma or space between codes. The instructions say “Don’t separate the codes by a space or comma.” Codes B and W, for instance, are written together in alphabetical order.

Sources

Instructions for Form 8949 (2025): https://www.irs.gov/pub/irs-pdf/i8949.pdf
Instructions for Schedule D (Form 1040) (2025): https://www.irs.gov/pub/irs-pdf/i1040sd.pdf

Read from the IRS documents linked above on October 17, 2026. General information, not tax advice. Your own facts decide the outcome, and a preparer, the account provider or the IRS is the right place to confirm anything consequential.