Modified adjusted gross income (MAGI) is your adjusted gross income (AGI), with changes required by a particular tax or benefit rule. There is no single MAGI formula. The number used for Roth IRA eligibility can differ from the one used for Medicare premiums or health-insurance assistance. To find yours, first identify which rule you are testing.
What is MAGI?
AGI is the income subtotal on your federal return after certain adjustments, such as an eligible HSA deduction. It comes before the standard or itemized deduction.
MAGI takes that subtotal and changes it for a specific purpose. Some rules add back income that is ordinarily tax-exempt. Others restore a deduction or remove income from a Roth conversion. Your tax return provides the starting point; the relevant worksheet supplies the adjustments.
Why do Roth, NIIT, IRMAA, and ACA MAGI disagree?
Each program measures income for a different purpose, so each defines its own adjustments:
| What you are checking | How its MAGI usually differs from AGI |
|---|---|
| Direct Roth IRA contributions | Subtracts taxable conversion income; adds back specified deductions and exclusions |
| Net investment income tax (NIIT) | Often equals AGI; foreign-income situations can require adjustments |
| Medicare’s income-related monthly adjustment amount (IRMAA) | Adds tax-exempt interest |
| Affordable Care Act (ACA) Marketplace assistance | Adds tax-exempt interest, excluded foreign income, and nontaxable Social Security |
For example, municipal-bond interest can be excluded from regular federal income tax while still affecting Medicare premiums. “Tax-exempt” does not mean ignored by every income test.
What does Roth IRA MAGI add back?
IRS Publication 590-A, Worksheet 2-1, starts with AGI and subtracts taxable Roth conversions and qualified-plan-to-Roth rollovers. It then adds specified items, including deductible traditional IRA contributions, student-loan interest deductions, certain foreign-income exclusions, excluded savings-bond interest, and excluded employer adoption benefits.
For 2026, the direct Roth contribution allowance phases out at $153,000–$168,000 for single or head-of-household filers and $242,000–$252,000 for joint filers. Married filing separately generally uses $0–$10,000 if you lived with your spouse during the year. The IRS 2026 retirement-limit announcement sets those ranges; compensation and annual contribution limits still apply.
A conversion can therefore increase your taxable income without using up your direct Roth contribution eligibility. It still has other tax effects. The Roth conversion income guide explains which calculations include it.
What does NIIT MAGI add back?
For many households, MAGI for the 3.8% net investment income tax equals AGI. Foreign earned-income exclusions and certain foreign investments can require adjustments; use the Form 8960 instructions if those apply.
The tax applies to the smaller of net investment income or the amount by which MAGI exceeds the threshold: $200,000 for single or head-of-household filers, $250,000 for joint filers, and $125,000 for married filing separately.
A Roth conversion is generally not net investment income itself. It can still raise MAGI enough to expose other investment income to NIIT. You need both numbers to calculate the tax.
What does IRMAA MAGI add back?
For Medicare premium surcharges, MAGI is AGI plus tax-exempt interest. Social Security generally uses a tax return from two years earlier: 2026 premiums usually depend on 2024 income. SSA’s MAGI policy explains the definition and lookback.
For 2026 premiums, the first surcharge generally begins above $218,000 for joint filers and $109,000 for individual filers. Married-filing-separately rules can differ. A conversion in 2026 would generally affect 2028 premiums; do not compare it with the 2026 premium thresholds and treat that as the final answer.
What does ACA MAGI add back?
For Marketplace premium assistance, MAGI generally adds tax-exempt interest, excluded foreign income, and nontaxable Social Security to AGI. Household income can also include the MAGI of dependents required to file a return. The Form 8962 instructions explain the calculation.
The coverage year matters. Estimate income for the year you receive coverage, and check that year’s eligibility and repayment rules. An earlier year’s worksheet can explain the income definition while containing benefit rules that no longer apply.
Why do people plan with the wrong MAGI?
The common mistake is reusing one income number for several decisions. These two examples show why the adjustments and years matter.
Municipal interest and Medicare: A couple’s 2024 joint return shows $210,000 of AGI and $12,000 of tax-exempt interest. Their Medicare MAGI is $222,000. When that return is used for 2026 premiums, the amount exceeds the $218,000 joint threshold even though AGI alone is below it.
A conversion and Roth eligibility: A couple’s 2026 AGI is $248,000, including a $30,000 taxable Roth conversion. Assume no other MAGI adjustments. Roth contribution MAGI is $218,000, below the 2026 joint phaseout. NIIT MAGI remains $248,000, and Medicare MAGI also remains $248,000 if there is no tax-exempt interest. Any Medicare effect generally belongs to a later premium year.
In each case, the same tax return produces different answers because the questions are different.
Which MAGI worksheet should you open?
Use Publication 590-A for Roth contributions, Form 8960 for NIIT, SSA’s AGI-plus-interest calculation for Medicare, and Form 8962 for Marketplace assistance.
Label each result with its purpose and income year. If you are close to a threshold, rerun that calculation before making a contribution, conversion, or sale. “MAGI: $218,000” is incomplete; “2026 Roth contribution MAGI: $218,000” tells you what the number can actually answer.