A taxpayer's overall tax liability is more complicated than simply identifying income and applying the corresponding federal income tax rate.

Instead of directly increasing ordinary income tax rates, the Internal Revenue Code adds taxes or takes away tax benefits for taxpayers with higher income levels. These provisions tend to sneak up on clients — by chipping away at the block of income they're entitled to keep.

Modified adjusted gross income is the key benchmark for determining whether many of these under-the-radar tax provisions will apply to increase overall tax liability. While MAGI is important for all taxpayers, its effects tend to be most significant for retirees and near-retirees.

Understanding the concept and its applications can be critical to minimizing tax liability and avoiding surprises.

Modified Adjusted Gross Income: the Basics

Congress has not adopted a uniform formula for calculating MAGI. Instead, the definition depends on the precise aspect of the Code that's involved.

At the most basic level, in calculating MAGI, taxpayers begin with their adjusted gross income on their Form 1040. They then add available tax benefits or income that would otherwise be received tax-free.

MAGI and Retirement: Understanding the Impact

Many working clients are unable to significantly reduce their MAGI — unless they elect to earn less or tie up more in accounts with restricted access.

Reducing taxable income via funding pre-tax accounts is always a smart idea, but that might not be sufficient for higher-income clients to fall below MAGI-related thresholds.

Retirees and pre-retirees who have executed tax-smart retirement plans have more control over their taxable income. They may have funded Roth accounts, giving access to income that won't increase MAGI — or can execute strategic Roth conversions at reduced income tax rates to create a tax-free income stream.

Certain Code provisions that invoke MAGI standards affect only retirees and those nearing retirement. For example, MAGI determines how a Social Security beneficiary's benefits will be taxed and the amount a Medicare beneficiary will pay for premiums.

The Medicare income-related monthly adjustment amount is a surcharge added to base-level Medicare Part B and Part D premiums for higher-income taxpayers. MAGI for IRMAA purposes is the taxpayer's adjusted gross income plus:

  • the taxable portion of Social Security benefits
  • tax-exempt interest
  • interest from U.S. savings bonds used for qualifying education expenses
  • nontaxable income from U.S. territories
  • any income earned abroad that was excluded from AGI.

In 2026, IRMAA affects single taxpayers with income greater than $109,000 and joint filers who earn more than $218,000.

Taxpayers with between $25,000 and $34,000 in MAGI are taxed on up to 50% of their Social Security benefits (the thresholds are $32,000 and $44,000 for joint filers). When combined income exceeds $34,000 ($44,000 for joint returns), up to 85% of their benefits are taxed. Social Security recipients who claim before their full retirement age are subject to an earnings test to determine how their benefits will be taxed.

Calculating MAGI for Social Security purposes requires adding back deductions that were previously taken from AGI — as well as adding back previously tax-exempt income.

The net investment income tax also affects retirees and pre-retirees who have accumulated substantial investment income. While the tax doesn't directly apply to retirement distributions, it does apply to other passive income sources. It is a 3.8% tax that applies to the lesser of total investment income or
MAGI above $200,000 ($250,000 for joint returns).

OBBBA Deductions and MAGI

The One Big Beautiful Bill Act created several provisions where MAGI is relevant. It increased the cap on state and local taxes to $40,000, but that figure starts to phase out once MAGI exceeds $500,000.

A $6,000 senior deduction phases out once MAGI exceeds $75,000 ($150,000 for joint returns).

The qualified tip income and qualified overtime deductions are phased out when MAGI exceeds $150,000 ($300,000 for joint returns).

MAGI is calculated in the same manner for all these deductions, by adding to AGI:

  • foreign earned income
  • foreign housing exclusion amounts
  • income received by residents of Puerto Rico or American Samoa from sources within those territories.

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