Adjusted Gross Income (AGI)
Income (including wages, interest, capital gains, income from retirement accounts, alimony paid to you)
adjusted downward by specific deductions (including contributions to deductible retirement accounts, alimony paid by you);
but not including standard and itemized deductions.
AGI is the number you write at the bottom of page 1 of your 1040 form, and then copy again to the top of page 2.
See the tax calculator.