It depends on the current condition is systems and finishes in the house. At the very least, plan on replacing carpet and appliances every 5 years, water heaters in 5-8 years and if HVAC is original, plan on replacing in 10 years. Divide those replacement costs by the expected useful life ( in months) an that will. Serve as a starting point for building a reserve fund. Alternatively, set the total amount aside now, and plan on $100-150 per month for the minor repairs and service calls. If your tenant is going to be responsible for minor maintenance like drain clogs and hvac servicing, $100 per month might be a good number.