If you have a net capital loss, up to $3,000 can be used to offset other income, including interest. You don't have to file a form, the capital loss will flow from Schedule D to Form 1040, page 1 line 7. Any loss above this amount will carry over to the subsequent year until used up or offset by capital gains. The calculation of your capital loss carry over will be verified by the IRS when you file your tax return.