As a non-tax-professional, you could come across some misconceptions when learning how to figure out your AGI. Knowing how to calculate AGI from W-2 form is an essential skill every taxpayer should possess. This is a crucial step in calculating and arriving at your taxable income and tax liability for a given tax year. When filing your tax return, you would always spot a column to figure out your adjusted gross income, or more commonly known as AGI.