If you rent part of your property, such as a room or a portion of the house, you must divide certain expenses between the part of the property used for rental purposes and the part of the property used for personal purposes, as though you actually had two separate pieces of property. You can deduct the expenses related to the part of the property used for rental purposes, such as home mortgage interest and real estate taxes, as rental expenses. You can also deduct as a rental expense a part of other expenses that normally are nondeductible personal expenses, such as utilities and home repairs (such as painting the outside of your house). You do not have to divide the expenses that belong only to the rental part of your property. For example, if you paint the room that you rent or pay premiums for liability insurance in connection with renting a room in your home, the entire cost is a rental expense. If you install a second phone line strictly for your tenant’s use, all of the cost of the second line that you pay is deductible as a rental expense. You can also deduct depreciation on the part of the property used for rental purposes, as well as on the furniture and equipment used for that purpose.
Generally, the most frequently-used methods of allocating expenses between personal use and rental use are: (1) based on the number of rooms in the home, and (2) based on the square footage of the home. You can use any reasonable method for dividing the expense. It may be reasonable to divide the cost of some items (for example, water) based on the number of people using them.