An amended return to claim a refund generally can be filed up to three years from the due date of that return (or the actual filing date if after the due date).
Gross income less allowable adjustments, such as IRA, alimony, and Keogh deductions. AGI determines whether various tax benefits are phased out, such as personal exemptions, itemized deductions, and the rental loss allowance and modified adjusted gross income (MAGI).