To actually claim the deduction for investment interest expenses, you must itemize your deductions. Investment interest goes on Schedule A, under "Interest You Paid." You may also have to file Form 4952, which provides details about your deduction. You don't have to file this form if you meet three conditions: interest is the only investment expense you're deducting; you're not carrying forward any disallowed interest from the previous year, and your investment interest doesn't exceed your investment income from interest and ordinary dividends. If the mortgage interest is enough you can amend previous years to claim it, and you can claim in year you sell, if you itemize