Fewer than one in ten Medicare beneficiaries pays an Income-Related Monthly Adjustment Amount, so a reader whose household income sits well under the first tier can stop here. Everyone else should keep reading. The first tier catches a single filer whose 2024 modified adjusted gross income tops $109,000, or a joint filer above $218,000, and it adds a 2026 surcharge to both Part B and Part D premiums.
The Scenario
A 67-year-old retiree files a single return for tax year 2024. Her adjusted gross income reads $108,400. She also collected $900 in tax-exempt municipal bond interest, which she assumed stayed invisible because it escapes federal income tax. The Social Security Administration adds that line 2a interest to her line 11 AGI, arrives at $109,300 of MAGI, and drops her into the first IRMAA bracket for 2026. Her January 2026 premium notice lands higher than she expected, and the surcharge rides every monthly premium for the rest of the year.
The Cliff, the Lookback, and the Math
IRMAA runs on a two-year income lookback, so 2024 MAGI sets 2026 premiums. Her 2024 return is already filed, which locks the 2026 surcharge in place. Looking ahead, 2025 income will drive 2027, and 2026 income will drive 2028. She cannot unwind income she has already reported, so only future-year MAGI stays within her control.
The first tier works as a cliff: one dollar over the threshold triggers the entire surcharge. For 2026, that surcharge arrives in two pieces:
- Part B adds $81.20 per month on top of the $202.90 standard premium, for a total of $284.10 per month.
- Part D adds $14.50 per month on top of whatever the plan charges.
Together they come to $95.70 per month, or about $1,148 per year, per person. When both spouses enroll and their joint return tops $218,000, each enrollee pays the surcharge separately.
The hold-harmless provision, which shields most beneficiaries from a net drop in their Social Security check when premiums rise, does not cover IRMAA payers. So a first-time move into a surcharge bracket can cut a retiree’s net Social Security income outright. The $1,148 figure only holds once you count Part D, and Part D is where many readers forget to look, because the surcharge bolts onto a private plan premium they already pay separately.
What Counts as MAGI
For IRMAA, MAGI means adjusted gross income (Form 1040, line 11) plus tax-exempt interest (line 2a). That definition runs narrower than it sounds and broader than it feels. A handful of items routinely push retirees across the line:
- Roth conversions. The conversion counts as fully taxable in the year you make it, so it lands in AGI.
- Required Minimum Distributions. RMDs from traditional IRAs and 401(k)s start at age 73 and count in full.
- Capital gains. A home sale above the $250,000 single or $500,000 joint exclusion, or a simple portfolio rebalance, flows into AGI.
- Tax-exempt municipal bond interest. It escapes federal income tax but still counts toward IRMAA.
- Interest and dividends. Treasury interest, bank interest, and dividends all count in full.
Social Security benefits enter MAGI through their taxable portion on line 6b, which reaches up to 85% of benefits for higher-income retirees. As annual COLAs lift those benefits, they gradually raise the MAGI of retirees who lean on Social Security for a meaningful share of their income, nudging some toward the first bracket without any change in their own behavior.
The Survivor Trap
The 2026 brackets run roughly twice as wide for joint filers as for singles. When one spouse dies, the survivor starts filing single the year after the death. Household income often falls by far less than half, because pensions and Social Security frequently continue at a reduced rate while spending needs hold steady. The same dollar of income that sat comfortably inside the joint zero-surcharge band can clear the single threshold the next year. The bracket moved; the income did not.
What SSA-44 Will and Will Not Do
Form SSA-44 lets a beneficiary ask the Social Security Administration to base the surcharge on more recent income instead of the two-year-old return. It applies only to qualifying life-changing events: marriage, divorce or annulment, death of a spouse, work stoppage, work reduction, loss of income-producing property, loss of pension income, or an employer settlement payment.
A Roth conversion does not qualify. A home sale does not qualify. An RMD does not qualify. A large capital gain from a portfolio rebalance does not qualify. The rules treat these as voluntary or anticipated, so the surcharge they trigger stays in place. SSA-44 only addresses income that has dropped.
Planning Levers
- Project your MAGI for the current tax year before December 31 by combining expected AGI, tax-exempt interest, and any planned Roth conversion or RMD. When the total lands within a few thousand dollars of $109,000 single or $218,000 joint, postponing discretionary income, such as a Roth conversion or a stock sale, or accelerating deductions can hold MAGI below the threshold.
- File SSA-44 as soon as a qualifying life event occurs. A life-changing-event request carries no fixed deadline, but filing promptly with supporting documentation, such as a retirement letter, a death certificate, a divorce decree, or a pension termination notice, gets your premium adjusted sooner. Include an estimate of the new year’s income.
- Weigh the surcharge before you convert when household income sits within roughly $20,000 of a bracket. A Roth conversion that looks efficient at a 22% or 24% marginal rate can cost more once you add a full year of IRMAA on both Part B and Part D and the extra taxable Social Security the conversion creates.
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