Business Use Percentage for Vacation Home Used for Personal Use

I have seen several posts on business use vs personal use days with some focused on 0 personal use days.  As such I am seeking clarification on how to count business use days and personal days.  If a vacation property is available for rent through an independent property manager for 9 months a year and the other three months are reserved for personal use days, are all days held for rent included as business use days?  Since we don't have 100% occupancy during the 9 months can we count all days or only the days rented? The full 3 months reserved for personal use are only partially occupied as well.