For most Americans, mortgage interest paid on a home loan is tax-deductible in the year in which it was paid. 

With advance planning, therefore, homeowners can increase their 2008 tax deductions and limit their tax liability on April 15.

The key is to make the January 2009 mortgage payment before the New Year begins.

In making the payment in 2008, the payment's mortgage interest is applied against this year's tax deductions instead of next year's.  And lest you think you're paying "in advance", remember that mortgage interest is paid in arrears; a payment due January 1 accounts for interest that accumulated in December 2008 anyway. 

Tax planning is a complicated issue and not all homeowners will qualify for mortgage interest tax deductions. Check with your tax professional before making tax planning decisions.