Adjusted Gross Income (AGI) is the basis for your income tax liability. It determines your qualifications for certain credits or deductions. If you're looking for your AGI from a previous year, it can be found on your tax returns (assuming you are using the standard Form 1040) on line 37 (the last dollar amount on the first page).
Calculate actual (gross) income. Actual income includes salary, interest earned, income from investments and basically any income you made through business, trade or investments. This is the basis for your AGI calculation. Your gross income is the money you earned through wages, interest, dividends, rental and royalty income, capital gains, business income, farm income, unemployment and alimony.
Once you have actual Income (gross income), you can "adjust" it to calculate AGI. Adjustments are taken by subtracting out qualified deductions from your gross income as calculated in Step 2. Adjustments can include items like some contributions to IRAs, moving expenses, alimony paid, self-employment taxes, and student loan interest. You can also use an AGI calculator to verify your results.