Schedule E - I rented out one room of my apartment for part of the year. I cannot figure out how to express that only a part of my apartment was rented. There's a way to say how many days it was rented, but no way to refer to the portion of my apartment t

To enter in TurboTax enter under the Property Profile indicate that you rented a part of your home on the page, Do Any of These Situations Apply to This Property? 

If you rented a part of your home and it was rented for the entire year, then TurboTax will calculate the rental/personal share.

If you rented part of your home and it was not rented for the entire year (you entered days rented and personal use), then you will need to allocated expenses between the rental and personal portion. Square footage is a common way to allocate. Ex: Room is 200 sq.ft/2000 sq.ft home = 10% of expenses allocated to the rental side.