the relative importance of the activities you perform at each place, and
the amount of time you spend at each place
If you spend more time at home than in other places, and perform your most important activities at home, your principal place of business is most likely your home.
If you use part of your home exclusively and regularly to meet or deal with patients, clients, or customers, your home does not necessarily have to be your principal place of business. As long as you physically meet with them on your premises, and their use of your home is substantial and integral to the conduct of your business, you will qualify to deduct expenses for the business use of your home.
If you have a separate structure such as a garage, barn, workshop, or studio, that you use exclusively and regularly for your business, you qualify for the deduction for business use of your home, even though it may not be your principal place of business and you do not meet with customers or clients there.
If you are an employee and perform work at home, there are two additional tests you have to meet:
The business use of your home must be for the convenience of your employer, and
You do not rent part of your home to your employer and use that space to perform services for your employer.
The two cases in which you do not have to meet the exclusive use test are when you use part of your home for the storage of inventory or product samples and when you operate a daycare facility from your home. In these two exception cases, that part of your home can be used for both personal and business purposes, without disqualifying you for the deduction.
If you use part of your home to store inventory or product samples, you must be in the business of selling those products at wholesale or retail, your home must be your only fixed business location, and you must use the storage space on a regular basis.
To qualify your home as a daycare facility, for purposes of the tax deduction, you must be in the business of providing daycare for children, persons age 65 or older, or persons who are unable to care for themselves. You must also have the necessary license, certification, or other approval to operate a daycare center under state law.