When I allocate the number of rooms for a home office, do I count the kitchen? And if the living room and dining room are sort of all one room, do I count as 2 rooms?

You can only claim expenses for a reasonable percentage of your home work space, not the entire home.

As per the Canada Revenue Agency (CRA),

"To determine your workspace use: 

All finished areas within the home count towards the size of the home. This includes:

• hallways
• bathrooms
• kitchen

If you have an open concept design, you would use a reasonable percentage of the open space as your work space. You cannot use the entire floor space as your work space.

To determine the percentage of your home that you use as a work space, use this formula:

Size of your work space divided by Size of your home times100 equals your work space as a % of your home."

The CRA has a calculator that will perform this calculation for you. 

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