If you rent out a room in your house, you can deduct 100% of your rental expenses including advertising fees, AirBnb fees, insurance, cleaning, repairs and other expenses related directly to the rental of that room.
You can also deduct a portion of the expenses related to your entire home (mortgage interest, insurance, etc.). However, these are prorated based on both how long the room was rented and the square footage ratio of the room to the entire home.
Example: You have a three bedroom house and rent out one of the rooms. If you rent this room for 100 days out of the 365 days, its rental usage is about 27%. Because you rented only one-third of your house for 27% of the year, you can deduct only 9% of the expenses that relate to your entire home (for example, mortgage interest).
If the expenses related to your entire home total $10,000, then you can deduct only $900. (9% of $10,000). However, any direct rental expenses such as advertising fees are 100% deductible.