What is form 8949 and Schedule D, when do I need to use this?

If you receive form 1099-B or 1099-S (or substitute statement) with the amounts that were reported to you and the IRS, you’ll need to use form 8949 to report any long-term capital gains/losses. The subtotals from this form will then be carried over to Schedule D (Form 1040), where gain/loss will be calculated in aggregate.