Every day that you "rent" to a family member below FMV is considered a day of personal use by you. If you have 14 or more days of personal use, then to the IRS you no longer have a rental property. In that circumstance, if your family member helps pay some of the expenses, then you have a cost-sharing arrangement - not rent. Cost-sharing between family members is not taxable income to you. Your relative isn't paying you; he's paying his share of the bills.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
