How AGI Is Calculated

The math is straightforward: AGI equals total income on line 9 minus the above-the-line adjustments on line 10. Those adjustments — retirement contributions, the deductible half of self-employment tax, HSA deductions, student loan interest, and others carried from Schedule 1 — reduce gross income before the standard deduction or itemized deductions are even considered. The result is a single figure that the IRS and state tax authorities use as the baseline for dozens of downstream calculations.

Why AGI Controls So Much of the Return

AGI determines whether a taxpayer qualifies for credits such as the Child Tax Credit, the Earned Income Tax Credit, education credits, and the premium tax credit for health insurance. It also triggers phaseouts on itemized deductions, IRA contribution deductibility, and Roth IRA eligibility. For high-income filers, AGI is the starting point for the 3.8% net investment income tax and the 0.9% additional Medicare tax. In short, two taxpayers with identical gross incomes can face very different tax outcomes depending on where AGI lands after line 10 adjustments.

AGI and New York City Taxpayers

For Reed Corporation clients — business owners, models and creators, athletes, expats, and high-net-worth individuals — AGI planning is often the single most consequential conversation of the year. New York State uses federal AGI as the starting point for its own income tax calculation, which means a higher federal AGI flows directly into higher state and city tax. Managing retirement contributions, timing capital gains, and structuring entity income to optimize AGI can produce meaningful savings across all three tax jurisdictions.

AGI vs. Modified Adjusted Gross Income (MAGI)

Several IRS provisions reference modified adjusted gross income rather than AGI. MAGI typically starts with AGI and adds back certain items — such as tax-exempt interest, excluded foreign earned income, or student loan interest — depending on the specific provision. Understanding the difference matters because a taxpayer who qualifies for a credit based on AGI may not qualify based on MAGI, or vice versa. The Reed Corporation reviews both figures when advising clients on contribution limits, credit eligibility, and phaseout thresholds.