When looking at a Form W-2, you would use Box 1 for total Federal income (assuming they have no other sources of income). If they don't have any above-the-line deductions, this would also be the Federal adjusted gross income.
Above-the-line deductions that would impact adjusted gross income include educator expenses, certain business expenses for reservists, performing artists and fee-based government officials, health savings account deduction, moving expenses, certain self-employment deductions, penalty on early withdrawal of savings, alimony paid, IRA deduction, student loan interest and tuition and fees deduction.
