IRS tax-return form where you list capital gain or loss transactions. The subtotals noted on Form 8949 are then used to complete Schedule D of the Form 1040 tax return for your aggregate gain or loss.

Both Form 8949 and Schedule D are required to report sales of securities when you have to make any type of adjustment in the cost basis or modification of the information reported on Form 1099-B. For details on that reporting, see the FAQs with annotated diagrams of Form 8949 and Schedule D in the Tax Center of this website.