MAGI (Modified Adjusted Gross Income)

MAGI is one of the most confusing terms in personal tax because it sounds like a single number but is actually a family of different calculations, each defined separately by the statute that uses it. The Premium Tax Credit for ACA marketplace coverage uses a MAGI that adds tax-exempt interest, untaxed foreign income, and the non-taxable portion of Social Security benefits to AGI. The Roth IRA contribution limit uses a MAGI that adds back the deduction for traditional IRA contributions, the deduction for student loan interest paid, and a few other items to AGI. The Net Investment Income Tax uses a MAGI that adds back the foreign earned income exclusion. These three MAGIs are not the same number; for many filers they are close, but for filers with tax-exempt municipal bond interest, untaxed Social Security benefits, or significant foreign income, the deltas matter.

The implication for planning: when a tax form or planning calculator asks for your MAGI, you cannot reuse a MAGI you computed for a different purpose. The IRS publishes form-by-form instructions for which add-backs apply — Form 8962 (Premium Tax Credit) has its own MAGI worksheet, Form 8606 (Nondeductible IRAs) references a different MAGI defined in IRC § 408A(c)(3), Form 8960 (Net Investment Income Tax) uses the § 1411 MAGI definition. Treating MAGI as one number can produce errors that the IRS catches months or years later, with interest.

For the most commonly encountered case — testing whether a household qualifies to make a direct Roth IRA contribution — the relevant MAGI starts with AGI from Form 1040 line 11, then adds back traditional IRA deductions, student loan interest deduction, foreign earned income exclusion, foreign housing exclusion or deduction, savings bond interest exclusion used for qualified education expenses, and the employer-provided adoption benefits exclusion. For most filers without foreign income or adoption benefits, the practical computation reduces to AGI plus any traditional IRA deduction taken plus any student loan interest deduction taken — usually a small adjustment, but enough to push some filers above the Roth contribution phase-out.

Because MAGI is the gating number for many high-value provisions (Roth eligibility, Premium Tax Credit, education credits, child tax credit phase-out), households near a threshold should always recompute the relevant MAGI before claiming or contributing, not rely on an estimate from a prior year. A household at $150,000 of AGI considering a maximum Roth IRA contribution should check their MAGI, not their AGI, against the Roth income limits — and if MAGI is close to the phase-out, consider strategies that reduce MAGI such as a larger traditional 401(k) contribution (which lowers AGI directly without an add-back to MAGI for Roth purposes) before resorting to the backdoor Roth path.

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