Can I deduct margin interest (investment interest expenses) from my capital gains? If so, where can I enter this?

Margin interest is deductible as an itemized deduction on Schedule A, up to the amount of your net taxable investment income, including capital gains.

 

You can enter your margin interest by following these steps:

 

1. In TurboTax Online, open your tax return
2. Click on Federal in the left-hand column, then on Deductions & Credits
3. Navigate to the list of Deductions & Credits
4. Locate the section Retirement and Investments and click Start on the right 
5. Click Start next to Investment Interest Expenses.

 

Please read this TurboTax article for more information.