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Form 1099-DA Box 1g: Cost or Other Basis and When It Is Blank

Updated October 17, 2026. Quick answer: Box 1g of Form 1099-DA shows the aggregate cost or other basis of the digital assets that were sold, exchanged or otherwise disposed of. It concerns anyone whose broker reported a disposition. A blank box means you work out basis from your own records, while any entry, including zero, was reported to the IRS as basis. The figure goes through Form 8949 and Schedule D.

Form 8949 for 2025, read code by code: Form 8949 code B, Form 8949 code E and Form 8949 code O.

What box 1g reports

The recipient instructions describe the box: “Shows the aggregate cost or other basis of the digital assets sold, exchanged, or otherwise disposed.”

This page covers the box itself; the proceeds are on Form 1099-DA box 1f. Whether the broker reported it to the IRS is the subject of Form 1099-DA boxes 2 and 9, and the other boxes are mapped in the Form 1099-DA boxes guide.

Blank, zero, or a number: three different messages

This is the most important part of the box, and the recipient instructions state it directly: “If box 9 is checked, box 1g may be blank if the cost or other basis was unknown to the filer or the digital assets were acquired prior to 2026.”

The 2025 recipient instructions word the same sentence with a comma: “box 1g may be blank if the cost or other basis was unknown to the filer, or the digital assets were acquired prior to 2026.”

What follows is the part that requires action: “If box 1g is blank, you will need to determine your basis based on your own books and records.”

And the opposite case: “If box 1g has any entry, including zero, the information within that box has been reported to the IRS as basis.” The broker is told to be careful with zero: “Enter -0- in box 1g only if the digital asset sold actually had a basis of zero.”

What the broker is told to enter

The broker’s instruction is: “Enter the adjusted basis of any digital asset sold unless the digital asset is not a covered security and you check box 9 and choose not to complete box 1g.” “If you check box 9 and are not reporting basis, leave box 1g blank.”

Transaction costs also matter to basis. For an exchange, the broker is told that “the digital asset transaction costs paid by the taxpayer to effect the exchange are allocable generally to the disposition of the transferred digital assets for purposes of determining basis.” See whether swapping one crypto for another is taxable for the question of whether the swap itself is a taxable event.

Which lot, and how the broker chooses

When you bought the same asset at different times and sold only some of it, the broker follows an order: “report the sale according to the customer’s adequate and timely identification of the digital assets to be sold.” “If no identification is provided at or prior to the time of the sale, you generally must first report the sale of the earliest units of the digital asset purchased by the customer.”

The units, dates and lot picked by the broker are in boxes 1c to 1e, covered at Form 1099-DA boxes 1c, 1d and 1e.

The broker instructions also say that “The average basis method is only available for digital assets that are also a tokenized security.”

Where box 1g goes on the return

Like the other numbered boxes, box 1g is entered through the line the form points to: “Indicates where to report this transaction on Form 8949 and Schedule D (Form 1040), and which checkbox is applicable.” The forms involved are Form 8949 and Schedule D; box 6, at Form 1099-DA box 6, shows the gain or loss type.

Boxes 1h and 1i, at Form 1099-DA boxes 1h and 1i, are the adjustments that sit beside basis. The first-page question on Form 1040 applies as well; the recipient instructions say a person who received this form generally should check the Yes box.

Edition and box numbers

The primary read for this page is the 2025 edition of Form 1099-DA with its Instructions for Recipient, the form a taxpayer received in early 2026 for tax year 2025. The 2026 edition was the one irs.gov served as current on 2026-10-17, and both editions were compared for box 1g. The recipient wording for box 1g is the same in both editions apart from one comma, which the quoted sentences above show. The ‘prior to 2026’ wording appears in both. The filer instructions add one sentence to the lot-selection passage in 2026: “Under current law, brokers may use customer-provided acquisition information solely for lot-selection purposes and not for reporting basis or acquisition dates.” The 2025 filer instructions do not contain it. The 2026 recipient instructions add a note near the box descriptions: “Boxes 1d, 1e, 1g, 1h, 1i, 2, 3a, 3b, 5, 6, 8, 9, 12a, and 12b may be blank if the broker is reporting sales of qualifying stablecoins or specified NFTs using an optional reporting method.” The 2025 recipient instructions have no such note. That note lists box 1g. Check the tax year printed on the form you received, because the edition behind your form decides which wording applies to you.

Common mistakes

  • Entering zero basis when box 1g is blank. The instructions say “If box 1g is blank, you will need to determine your basis based on your own books and records.”
  • Treating a zero in box 1g as a missing figure. The instructions say “If box 1g has any entry, including zero, the information within that box has been reported to the IRS as basis.”
  • Forgetting that fees can sit inside basis. The broker is told that transaction costs “are allocable generally to the disposition of the transferred digital assets” when determining basis.

Related: Form 8949, Schedule D, swapping one crypto for another, and Form 1099-B proceeds and cost basis.

Sources

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.

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