It's fairly easy to compute the business percentage of your home for IRS purposes.
You'll need the total area of your home and the total area of your office in the home.
Assuming you have a 2000 sq ft home (maybe 50 by 40), you might measure your office to be 10 by 20, or 200 sq ft. Then, the business percentage is 200/2000 or 10%.
Since you just bought a house, you know its basis less the cost of the land.
If you paid $300,000 for house and land with the land worth 50,000, the house basis is
You would take home office depreciation of $25,000 over 39 years, which comes to
$641 per year.
Download and review the following IRS Publication on Office in Home expenses for further clarification and examples. It's a handy publication to keep in your office.
Do contact me again if you have any questions.