No double-dipping on mortgage interest

Q. I have a home office for my own business. Can I deduct mortgage interest in addition to the interest claimed on the personal part of my return? A.L., Kalamazoo, Mich.

A. Yes, but you must reduce the personal mortgage interest claimed on Schedule A by the amount of interest claimed on Schedule C.

For instance, let’s say the business portion of the home is 10 percent and you paid $5,000 in qualified mortgage interest in 2006. Claim the $500 mortgage interest deduction (10 percent of $5,000) on Form 8829. Include this amount in the home-office deduction from Schedule C entered on Line 12 of Form 1040. Then enter $4,500 ($5,000 minus $500) on Line 10 of Schedule A. In other words, you can’t “double dip” on your return.

Tip: The same basic rule applies to deductions for property taxes.