In TurboTax Premium Online, within the rental activity, at the screen Here's rental property info, select the pencil icon to the right of Rental property info.
At the screen Review your rental property info, select Days rented.
To clarify, we only rented 10% of our home (carriage house only rented). How does the software let you claim just 10% of the expenses (or do you have to manually calculate)?
When you enter the rental profile, since there is more than one unit on the property, and you live in one unit and rent the other (carriage house) select "I rent out a unit in a multi-unit property (like a duplex) where I live" on the "Do Any of These Situations Apply to This Property?" screen.
Continue through this interview until you get to the "Let Us Calculate Your Expense Deductions for You" screen and select your option, to have TurboTax allocate the expenses or for you to enter only the rental portion of expenses.