Social Security benefits do count toward IRMAA, but only the part of your benefits the IRS treats as taxable. For most retirees with enough income to be near an IRMAA threshold, that means up to 85% of the annual Social Security check feeds into the modified adjusted gross income (MAGI) figure Medicare uses to decide whether you owe a surcharge on Part B and Part D premiums. The other 15% (or more, for lower-income retirees) stays out of the calculation entirely.
How the Taxable Portion Reaches Your MAGI
Social Security enters the IRMAA formula through your tax return, not directly. The IRS first determines how much of your annual benefit is taxable using your combined income, which is half your Social Security plus all your other income. Once you clear the adjusted base amount — $34,000 for single filers, $44,000 for joint filers — up to 85% of your benefits become taxable.1Office of the Law Revision Counsel. 26 USC 86 – Social Security and Tier 1 Railroad Retirement Benefits
That taxable slice lands in your adjusted gross income, which is the starting point for the MAGI figure Social Security uses to set your Medicare surcharge.2Office of the Law Revision Counsel. 42 USC 1395r – Amount of Premiums for Individuals Enrolled Under This Part So a bigger Social Security check does push your MAGI up, but not dollar for dollar. Someone collecting $30,000 a year in benefits and sitting above the 85% threshold sees roughly $25,500 of that count toward IRMAA, not the full $30,000.
In practice, nearly every retiree with enough income to trigger IRMAA is already in the 85% bracket for Social Security taxability. Those base amount thresholds haven’t been adjusted for inflation since they were set in 1983 and 1993, so they pull more retirees over the line every year.
What Else Gets Added to Reach MAGI
MAGI for IRMAA starts with adjusted gross income, then adds back several categories of income that would otherwise escape the calculation:2Office of the Law Revision Counsel. 42 USC 1395r – Amount of Premiums for Individuals Enrolled Under This Part
- Tax-exempt interest, such as earnings from municipal bonds
- Foreign earned income excluded under the foreign earned income exclusion
- Income from U.S. savings bonds used for education expenses
- Nontaxable income from U.S. territories like Puerto Rico and Guam
The tax-exempt interest add-back is the one that surprises people. If you hold a sizable municipal bond portfolio, that interest never shows up in your adjusted gross income, but it counts in full for IRMAA. The rule is designed to capture income you actually have access to, even when it isn’t federally taxed.
The Income Streams That Usually Matter More Than Social Security
Because only the taxable portion of Social Security counts, benefits alone rarely push someone across an IRMAA threshold. What usually does the pushing is everything else on the tax return:
- Required minimum distributions. Starting at age 73, mandatory withdrawals from traditional IRAs and 401(k) accounts are fully taxable and flow straight into AGI. The year RMDs begin is when many retirees first hit IRMAA, especially if they delayed the first distribution and had to take two in one calendar year.
- Pension income. Payments from traditional defined-benefit plans are generally taxable and included in AGI.
- Capital gains. Selling investments, real estate, or a business creates a one-time spike. Because IRMAA looks at a single tax year, even a one-off sale can trigger surcharges for a full twelve months.
- Roth conversions. Converting traditional retirement funds to a Roth creates taxable income in the conversion year and can temporarily lift you into a higher IRMAA bracket.
- Tax-exempt interest. Not in AGI, but added back for MAGI as noted above.
The interaction is what matters. A retiree with $28,000 in Social Security, $40,000 from a pension, and $50,000 in RMDs can clear the first IRMAA threshold without touching a taxable investment account.
2026 IRMAA Thresholds
To see whether the taxable portion of your Social Security actually pushes you into surcharge territory, compare your MAGI to the 2026 brackets. In 2026, single filers with MAGI above $109,000 and joint filers above $218,000 pay an IRMAA surcharge on top of the standard Part B premium of $202.90 and the national base Part D premium of $38.99.3Centers for Medicare & Medicaid Services. 2026 Medicare Parts A and B Premiums and Deductibles
The Part B surcharge for singles starts at $81.20 per month just above $109,000 and rises through five more tiers to $487.00 per month at MAGI of $500,000 or more. Joint-filer thresholds run roughly double the single amounts, topping out at $750,000. Part D surcharges follow the same income tiers, ranging from $14.50 to $91.00 per month in 2026, and are added to whatever your Part D plan charges.3Centers for Medicare & Medicaid Services. 2026 Medicare Parts A and B Premiums and Deductibles
One boundary worth flagging: married couples who file separately and lived together at any point during the tax year face a much steeper structure — just three tiers, with the surcharge jumping to $446.30 for Part B as soon as MAGI passes $109,000. Spouses who lived apart for the entire year and file separately use the single-filer brackets instead.3Centers for Medicare & Medicaid Services. 2026 Medicare Parts A and B Premiums and Deductibles
The Year That Actually Counts Is Two Years Back
IRMAA doesn’t use your current income. The Social Security Administration pulls MAGI from the tax return you filed two years earlier through an automated data exchange with the IRS. For 2026 premiums, the agency looks at your 2024 return. For 2027 premiums, it will use 2025.2Office of the Law Revision Counsel. 42 USC 1395r – Amount of Premiums for Individuals Enrolled Under This Part
That lag catches people two ways. If you had one unusually high-income year — a home sale, a big Roth conversion, an option exercise — the surcharge arrives two years later, often after the money is spent. And if your income has genuinely dropped since retirement or a spouse’s death, you keep paying surcharges based on the old, higher number. The first problem resolves itself as the high-income year rolls off. The second may qualify for immediate relief.
Getting a Reduction If Your Income Has Dropped
Social Security lets you ask for a new determination using a more recent year’s income if you have experienced one of eight qualifying life-changing events:4Social Security Administration. Life Changing Events
- Death of a spouse
- Marriage
- Divorce or annulment
- Work reduction
- Work stoppage
- Loss of income-producing property, including from natural disaster or fraud
- Loss of pension income
- Employer settlement payment, such as from an employer bankruptcy
You file Form SSA-44 with documentation of the event, such as a death certificate, divorce decree, or letter from your employer, plus either the tax return for the more recent year or an estimate of your reduced income. If you use an estimate, you’ll need to provide the actual return once it’s filed.5Social Security Administration. Medicare Income-Related Monthly Adjustment Amount – Life-Changing Event Form SSA-44
This is technically a “new initial determination,” not an appeal. A new determination uses updated income data to recalculate the surcharge; a formal appeal argues the original calculation was wrong. You can also request a new determination if the IRS data was inaccurate or you filed an amended return.6Social Security Administration. Overview of New Initial Determinations on the Income-Related Monthly Adjustment Amount Using Beneficiary Provided Information If you want to challenge a determination you believe is simply wrong and don’t qualify for a new determination, you have 60 days from receiving the notice to request reconsideration.7Social Security Administration. Overview of the Appeals Process for the Income-Related Monthly Adjustment Amount
Keeping Your MAGI Below a Bracket
You can’t change how Social Security is taxed, but you have some control over the other income that pushes MAGI over a threshold. A few approaches are worth thinking through well before Medicare enrollment.
Roth conversions before age 63. Conversions create taxable income in the year they happen, but future Roth withdrawals are tax-free and stay out of MAGI. Because of the two-year look-back, conversions done before age 63 don’t touch your Medicare premiums at initial enrollment at 65. Spreading conversions across several lower-income years keeps each year’s MAGI under a bracket while gradually moving assets into the tax-free bucket.
Qualified charitable distributions. Starting at 70½, you can direct up to $105,000 per year (2024 limit, adjusted annually for inflation) from a traditional IRA straight to a qualified charity. The QCD satisfies your RMD but is excluded from AGI entirely. For retirees who plan to give anyway, it is one of the cleanest ways to keep RMDs from inflating MAGI.
Timing large income events. If you’re planning a rental sale, a stock option exercise, or a large retirement account distribution, look at when the income will land relative to the two-year lag. Bunching a sale into a year that is already going to trigger IRMAA is better than creating a second high-income year and paying surcharges for another twelve months.
The cliff effect. IRMAA brackets don’t phase in. Being $1 over a threshold means paying the full surcharge for that tier for the whole year. A single filer at $109,001 pays $81.20 more per month than someone at $109,000 — $974.40 over the year. If you’re close to a boundary, small moves like trimming a traditional IRA withdrawal or harvesting a capital loss can hold you in the lower tier.