Adjusted Gross Income (AGI): Definition and How It Works
Adjusted Gross Income (AGI) is the figure that results after subtracting specific above-the-line deductions from a taxpayer's total gross income. Under IRC §62, AGI serves as the foundational income measure used to calculate eligibility for, and phase-out of, dozens of tax provisions — from the standard deduction to the child tax credit to Roth IRA contribution limits. For CPAs, AGI is the number that sits at the bottom of the first page of Form 1040, and it is the starting point for almost every income-sensitive tax planning conversation.
How AGI Is Calculated
Gross income (IRC §61) includes wages, salary, business profits, rental income, interest, dividends, capital gains, alimony (for pre-2019 divorce agreements), and any other accession to wealth. From that total, taxpayers subtract above-the-line deductions — so called because they appear before the AGI line on Form 1040 — to arrive at AGI. These deductions do not require itemizing; they reduce AGI regardless of whether the taxpayer takes the standard or itemized deduction.
Common above-the-line deductions under IRC §62:
- Self-employed health insurance premiums — deductible in full for the taxpayer, spouse, and dependents (IRC §162(l))
- Self-employment tax deduction — 50% of SE tax is deductible as an above-the-line adjustment (IRC §164(f))
- Retirement plan contributions — SEP IRA, SIMPLE IRA, and solo 401(k) contributions made by self-employed individuals; Traditional IRA contributions up to the applicable limit for those not covered by a workplace plan (or covered plans below the income phase-out)
- Alimony paid — only under divorce or separation instruments executed before January 1, 2019
- Student loan interest — up to $2,500, phasing out above certain MAGI thresholds
- Health Savings Account contributions — above-the-line for individuals contributing to an HSA outside of employer payroll deduction (IRC §223)
- Educator expenses — up to $300 for K-12 educators
- OBBBA above-the-line deductions — the One Big Beautiful Bill Act (2025) created several new above-the-line deductions processed on the new IRS Schedule 1-A, including qualified tip income (up to $25,000), qualified overtime premium pay, and qualifying car loan interest (up to $10,000 on U.S.-assembled vehicles purchased 2025–2028)
Why AGI Matters: Phase-Outs and Thresholds
AGI (or Modified AGI/MAGI, which adds back specific deductions depending on the calculation) governs eligibility and benefit levels for dozens of provisions. Key examples:
| Provision | AGI/MAGI Phase-Out |
|---|---|
| Traditional IRA deductibility (covered by workplace plan) | $79,000–$89,000 single; $126,000–$146,000 MFJ (2026) |
| Roth IRA contribution eligibility | $150,000–$165,000 single; $236,000–$246,000 MFJ (2026) |
| Child Tax Credit phase-out | $200,000 single; $400,000 MFJ |
| QBI deduction W-2 wage limitation onset | $197,300 single; $394,600 MFJ (2026) |
| SALT cap ($40,000) phase-out | Above $500,000 MAGI (2026) |
| Net Investment Income Tax (NIIT, 3.8%) | Above $200,000 single; $250,000 MFJ |
| Medicare IRMAA surcharges | Multiple brackets above $106,000/$212,000 |
Because AGI drives so many downstream calculations, reducing AGI is often more valuable than increasing itemized deductions. Every dollar of above-the-line deduction may unlock additional credits and deductions that phase out based on AGI, creating multiplier effects in tax planning.
MAGI vs AGI
Modified Adjusted Gross Income (MAGI) is AGI with certain deductions added back. Each tax provision defines MAGI differently — there is no single MAGI figure. Common add-backs include the IRA deduction itself (for Roth eligibility), student loan interest, excluded foreign income, and excluded employer-provided adoption assistance. CPAs must apply the correct MAGI definition for each provision.
Tax Planning Implications
The most common AGI reduction strategies for CPA clients:
- Maximize retirement plan contributions: The fastest path to a meaningful AGI reduction, especially for self-employed clients using a solo 401(k) or SEP IRA — where contributions can reach $70,000 (2025) or more depending on income and plan type
- HSA contributions: Triple-tax-advantaged and above-the-line, reducing AGI while building a future medical expense account
- Timing income recognition and deductions: Business owners on cash accounting can accelerate deductions or defer income across year-end to manage AGI in a specific year
- Qualified Opportunity Zone investments: Deferring capital gain recognition reduces AGI in the year of investment
- Installment sales: Spreading gain recognition across years keeps AGI in lower brackets and away from NIIT thresholds
For strategies to reduce AGI for self-employed clients, see How to Minimize Self-Employment Tax. For how AGI affects the choice between standard and itemized deductions, see Standard Deduction vs Itemized Deductions.
Related Terms
- Self-Employment Tax — the half-deduction for SE tax is one of the most impactful above-the-line reductions for self-employed clients
- Pass-Through Entity — income from pass-through entities flows to owners' AGI, making entity-level tax planning central to individual AGI management
- QBI Deduction — the Section 199A deduction phases in limitations based on taxable income (AGI minus standard/itemized deduction), making AGI management critical for pass-through clients near the threshold
How CPAs Use AGI in Practice
AGI planning is a year-round activity, not just a tax-season calculation. CPAs use mid-year AGI projections to evaluate whether clients are approaching phase-out thresholds, whether Roth conversion makes sense in a given year, whether the NIIT will apply to an upcoming sale, and whether estimated tax payments need adjustment. For businesses, the entity structure choice — especially S-Corp election — has a direct impact on the owner's individual AGI through the interplay of salary, distributions, and above-the-line deductions.