To determine home office depreciation do I enter the cost of what I paid for my entire home or just the cost of the improvements made to construct my home office?

[ginotrapani]

Specifically, the section asks: "the cost of your entire home, the cost of the improvement." So, assuming I bought the entire house for $500K three years ago and converted a third garage bay into a home office which cost an additional $3K (right after the home purchase). Which number do I use? And, do I factor the cost of land at the time of purchase and subtract that? Thanks.

[DanO]

Use the cost of the home since the garage is included in the purchase price of the house. 

However much percentage of space the garage office takes in relation to the entire house is the amount of depreciation you can take based on that percentage times the $500,000 / 27.5 years.

The $3,000 you spent on building the office will be added to your business as a new asset which you will depreciate.

Subtract the value of the land when figuring the depreciation since land does not depreciate.

Any additional improvements to your home can also be depreciated in the amount proportionate to your home office.