Deductibility and Incentives to Promote Learning Opportunities and Maximize Assistance Act of 2012 or the DIPLOMA Act of 2012 - Amends the Internal Revenue Code to: (1) allow an unlimited tax deduction for qualified tuition and related expenses for taxpayers whose adjusted gross incomes do not exceed $80,000 ($160,000 for joint returns), (2) extend such deduction through 2017, (3) allow a tax deduction for principal amounts paid on education loans for the first 60 months of such loans, and (4) extend the American Opportunity tax credit through 2017.