Taxpayers need their filing status and AGI to calculate their phase-out amount. For example, say a taxpayer files as head of household and has an AGI of $375,000. In tax year 2013, she made charitable contributions of $20,000 and paid $30,000 of mortgage interest. Her total itemized deductions are $50,000. Calculate her excess AGI by subtracting her $275,000 AGI threshold from her $375,000 AGI to get $100,000. Multiply the excess AGI of $100,000 by 3 percent to get the $3,000 itemized deduction phase-out amount. Of her $50,000 total itemized deductions, only $47,000 can be listed on her Schedule A.