How to Calculate MAGI: Add-Backs, Thresholds, and Examples

To calculate your Modified Adjusted Gross Income (MAGI), start with the Adjusted Gross Income shown on Line 11 of your Form 1040 and add back a specific list of deductions and exclusions set by whichever federal program or tax rule you’re checking against.¹ There is no single MAGI formula. The IRS uses different add-back lists for Roth IRA eligibility, Affordable Care Act premium tax credits, Medicare surcharges, and other programs, so the first question isn’t how to add — it’s which list you’re supposed to use.²

Start With Your AGI

Every MAGI calculation begins with the same number. AGI is your total income from all sources minus a specific set of deductions federal law allows before your tax is figured.³ Line 11 of Form 1040 is where it lands.¹

To see how the IRS got there, look at Schedule 1. It lists additional income (business earnings, unemployment compensation, rental income) and the adjustments subtracted from it (educator expenses, HSA contributions, student loan interest). Some of the adjustments on that schedule are the same items you’ll add back to reach MAGI. If your AGI is off, every MAGI calculation built on top of it is off too, so confirm your income sources and Schedule 1 adjustments match your records before doing anything else.

The Add-Backs That May Apply

Add-backs are deductions or exclusions you already claimed. Putting them back gives the government a fuller picture of the money that was actually available to you. Not every item applies to every program; treat the following as the menu you draw from, not a checklist to run through every time.

Student Loan Interest Deduction

If you deducted student loan interest, that amount (up to $2,500) gets added back for several MAGI definitions, including Roth IRA eligibility and traditional IRA deduction limits.⁴

Foreign Earned Income and Housing Exclusions

If you worked abroad and excluded foreign earnings using Form 2555, the excluded amount goes back in. For 2026 the maximum foreign earned income exclusion is $132,900.⁵ Foreign housing exclusions and deductions add back under the same logic.

IRA Deduction

Traditional IRA contributions you deducted are added back when figuring MAGI for Roth IRA contribution eligibility and for the traditional IRA deduction itself.² The IRS wants to see your income before any IRA tax break was applied.

Tax-Exempt Interest

Interest from municipal bonds and similar tax-exempt investments doesn’t hit taxable income, but it does add back for ACA premium tax credits and Medicare IRMAA.⁶ A large muni portfolio can push MAGI well above AGI.

Nontaxable Social Security Benefits

Depending on total income, part or all of your Social Security may be tax-free. For ACA and Medicaid eligibility, the nontaxable portion is added back.² Retirees who assume their modest taxable income qualifies them for Marketplace subsidies sometimes find their MAGI tells a different story.

Savings Bond Interest and Adoption Benefits

Excluded savings bond interest used for higher education (Form 8815) and excluded employer-provided adoption benefits (Form 8839) both add back for retirement-account MAGI.⁷ They affect fewer people, but when they apply, skipping them throws off the number.

Which Add-Backs for Which Program

This is the part most guides gloss over, and it’s where the calculation actually diverges. Using the wrong add-back list is the common expensive mistake.

Roth IRA and Traditional IRA

Start with AGI and add back the student loan interest deduction, the IRA deduction, foreign earned income and housing exclusions, excludable savings bond interest, and excluded employer adoption benefits. Then subtract any income from Roth conversions or rollovers from qualified plans to a Roth IRA.² Tax-exempt interest and nontaxable Social Security are not on this list. Publication 590-A includes a worksheet you can follow line by line.⁷

ACA Premium Tax Credits

Take your AGI and add back only three things: foreign earned income, tax-exempt interest, and nontaxable Social Security benefits.² Student loan interest, IRA deductions, and savings bond exclusions don’t matter here. The same taxpayer can have a lower MAGI for ACA purposes than for Roth IRA purposes, or the reverse, depending on which income items apply.

Medicare IRMAA Surcharges

Medicare uses AGI plus tax-exempt interest, pulled from your tax return two years prior. Your 2024 MAGI determines your 2026 Medicare premiums.⁸ The two-year lag catches retirees off guard. A one-time spike from selling a business or taking a large distribution in 2024 shows up in 2026 premiums even if current income is much lower.

Net Investment Income Tax

The 3.8% surtax on net investment income kicks in when MAGI exceeds $200,000 for single filers or $250,000 for joint filers.⁹ The thresholds are not adjusted for inflation. The tax applies to the lesser of your net investment income or the amount by which MAGI exceeds the threshold.¹⁰

Rental Real Estate Loss Allowance

The $25,000 special loss allowance for rental property has its own MAGI definition, adding back passive activity losses, taxable Social Security, IRA deductions, student loan interest, and several other items.¹¹ The allowance phases out between $100,000 and $150,000 of MAGI and disappears at $150,000.

A Worked Example

A single filer with an AGI of $148,000 wants to know whether she can contribute the full amount to a Roth IRA in 2026. She claimed a $2,500 student loan interest deduction and a $4,000 traditional IRA deduction.

For Roth IRA purposes, both add back: $148,000 + $2,500 + $4,000 = $154,500. The single-filer Roth phase-out starts at $153,000 and ends at $168,000 in 2026, so she falls in the partial-contribution range and cannot contribute the full $7,500.¹²

If the same filer were checking ACA subsidy eligibility, neither of those add-backs would apply. Her MAGI for that purpose would remain $148,000. Same person, same tax return, two different MAGIs.

The steps generalize:

Find AGI on Line 11 of Form 1040.
Identify the correct add-back list for the specific program.²
Pull each relevant add-back amount from your return or schedules.
Add them to AGI. For Roth IRA calculations, also subtract any Roth conversion income.
Compare the result against the relevant threshold.

What Happens If You Get It Wrong

Miscalculating MAGI has consequences beyond an awkward correction later.

Excess Roth contributions. If your true MAGI is higher than you thought and you contributed more to a Roth IRA than allowed, the IRS charges a 6% excise tax on the excess amount for every year it stays in the account.¹³ You can avoid the penalty by withdrawing the excess plus earnings before your filing deadline, including extensions. Miss that window and the 6% keeps accruing annually.

Premium tax credit repayment. If you underestimated MAGI when applying for Marketplace coverage, you may have received larger advance premium tax credits than you were entitled to. When you file, the IRS requires you to repay some or all of the excess, with the amount depending on how far you overshot and on your filing status.

Unexpected Medicare surcharges. Because IRMAA uses MAGI from two years earlier, a single high-income year can trigger surcharges long after that income is spent. Selling an investment property or taking a large IRA distribution in 2024 can mean hundreds of extra dollars per month in Medicare premiums starting in 2026.

Estimated tax penalties. For taxpayers whose AGI exceeded $150,000 in the prior year ($75,000 if married filing separately), the safe harbor for avoiding underpayment penalties requires paying at least 110% of the prior year’s tax liability through withholding or estimated payments.¹⁴ When MAGI climbs and triggers additional taxes like the NIIT, your bill grows in ways paycheck withholding doesn’t cover. Running the calculation mid-year gives you time to adjust estimated payments before penalties pile up.

1
Internal Revenue Service. Adjusted Gross Income
2
Internal Revenue Service. Modified Adjusted Gross Income
3
Office of the Law Revision Counsel. 26 USC 62 – Adjusted Gross Income Defined
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Internal Revenue Service. Tax Topic 456 – Student Loan Interest Deduction
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Internal Revenue Service. Figuring the Foreign Earned Income Exclusion
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HealthCare.gov. Modified Adjusted Gross Income (MAGI)
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Internal Revenue Service. Publication 590-A, Contributions to Individual Retirement Arrangements (IRAs)
8
Centers for Medicare & Medicaid Services. 2026 Medicare Parts A and B Premiums and Deductibles
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Office of the Law Revision Counsel. 26 USC 1411 – Imposition of Tax
10
Internal Revenue Service. Net Investment Income Tax
11
Internal Revenue Service. Instructions for Form 8582 (2025)
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Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026; IRA Limit Increases to $7,500
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Internal Revenue Service. Retirement Topics – IRA Contribution Limits
14
Internal Revenue Service. Underpayment of Estimated Tax by Individuals Penalty