I have a home office for my carpentry business. The physical work is on job sites mostly, but all other related work id done from my office. What percentage do I use?

You have two choices for how to claim a home office deduction.  The "Simplified" of the "Regular" method.  For more information go to: Home Office Deduction

Actually, you're asked two questions related to "percentage" when it comes to home office use.

- Percentage of time the home office is used for the business. This will generally be 100% (one hundred percent). In other words, that office is used *only* for business stuff, and nothing else. You may only be in that office for 1 hour a week. But for that one hour each week it is one hundred percent business use. So if the kids use it for doing their homework or playing video games or whatever, then it's not used 100% of the time for business.

 - percentage of business conducted in the home office. This will be less than 100% since not all of the business you conduct or work you perform for the business, is actually done in that office.