Ah, I see what you're referring to now. When it comes to the percentage of space being rented, that's fairly fixed. It's the "other stuff" where you have choices. Lets use utility expenses for example.
If you have a 3 bedroom house and there's just you and your spouse living there with no kids, that's fair to say you have 2 "vacant" bedrooms. So you rent out one of the bedrooms to a married couple. At this point you have 4 people living in the house. You have two ways to claim the rental portion of your utility expenses.
1) With four people living in the house you can split them "per-person". With 2 of the four occupants being renters, you can allocate 50% of your utility expenses (water, gas, electric, cable) to the rental.
2) With only one bedroom being rented, lets say that's 10% of your total floorspace allocated as the rental portion. You can claim choose to allocate your utility expenses the same way and claim 10% of your total utility expenses to the SCH E for the rental portion.
You can do whichever works best for you. Some other things to keep in mind too.
Let's say you have 2 full baths in the house, and one of those baths can only be access from the bedroom being rented. That makes the floorspace for the bath "exclusive to the renter" also. Therefore it can be included in the percentage of floor space being rented.
Let's say you only have one wired land line telephone in your house. This is weird, but the IRS says you can't allocate that. Not even if there's a phone drop in the room being rented out. You'd have to have a 2nd phone line.
If you have cable or satellite TV, then you have to have a drop for that in the room being rented. Then you can claim a portion for the rental weather the renter uses it or not. Typically you'd need a separate cable/satellite box at the drop for that room. So the cost you pay for that box would be a SCH E deduction with no problem, weather it's a one time fee or a monthly fee you pay for that extra box.
Most folks around my area that rent rooms have a completely separate satellite TV setup with it's own separate dish antenna, and they just cancel the subscription when the renter vacates. Sometimes the renter will choose to activate it in their name and their own account, which is fine too. Then it's no concern of the landlord. Just make sure they don't take it with them when they vacate. 🙂
