The most important constraint on Roth conversion sizing for a retiree on Medicare is not the income-tax bracket — it’s the IRMAA cliff. The Income-Related Monthly Adjustment Amount (IRMAA) is a surcharge added to Medicare Part B and Part D premiums when a retiree’s Modified AGI crosses one of five tiered thresholds. The tier system is a hard cliff, not a phase-in: $1 over the threshold triggers the full surcharge for both spouses for the entire year.
Worse, IRMAA looks back two years to determine the current year’s premium. A 2026 Roth conversion that pushes MAGI $1 over the 2026 first-tier threshold of $109,000 (single) triggers higher Part B and Part D premiums in 2028 — by which time the conversion strategy is locked in and the retiree has no opportunity to course-correct.
This guide walks through the 2026 IRMAA brackets, the conversion-sizing decision framework, and the appeal/refund mechanic when life circumstances change. For the broader Roth-conversion decision logic see Roth Conversion: When Does It Make Sense? and the Roth Conversion Calculator which models the IRMAA cascade explicitly.
1. The 2026 IRMAA brackets
Five tiers above the base threshold. Each tier adds both a Part B surcharge (which the retiree pays) and a Part D Income-Related Monthly Adjustment (added to whatever Part D plan premium they have).
Single filer
| MAGI tier | Part B monthly surcharge | Part D IRMA | Annual total per person |
|---|---|---|---|
| ≤ $109,000 | $0 | $0 | $0 (base premium only) |
| $109,001 – $137,000 | $74.20 | $13.70 | $1,054.80 |
| $137,001 – $171,000 | $185.50 | $35.30 | $2,649.60 |
| $171,001 – $205,000 | $296.90 | $57.00 | $4,247.40 |
| $205,001 – $500,000 | $408.20 | $78.60 | $5,841.60 |
| > $500,000 | $445.40 | $85.80 | $6,374.40 |
Married filing jointly
| MAGI tier | Part B monthly surcharge | Part D IRMA | Annual total per couple |
|---|---|---|---|
| ≤ $218,000 | $0 | $0 | $0 |
| $218,001 – $274,000 | $74.20 | $13.70 | $2,109.60 |
| $274,001 – $342,000 | $185.50 | $35.30 | $5,299.20 |
| $342,001 – $410,000 | $296.90 | $57.00 | $8,494.80 |
| $410,001 – $750,000 | $408.20 | $78.60 | $11,683.20 |
| > $750,000 | $445.40 | $85.80 | $12,748.80 |
For 2026 these brackets are based on 2024 inflation indexing of the bracket pegs that began with the 2020 base. The $1 cliff means a single filer with MAGI of $109,001 pays $1,054.80 more in 2028 than one with MAGI of $109,000 — same as paying a 105,480% marginal “tax” on that $1.
2. The 2-year look-back
IRMAA in any year uses the MAGI from the tax return filed two years prior. The chain:
- 2026 MAGI is determined when you file your 2026 return in 2027.
- That return is shared with the Social Security Administration via SSA-1040 data feed (this is automatic; no separate filing required).
- 2028 Medicare premiums are calculated from the 2026 return.
The implication: every Roth conversion decision affects Medicare premiums two years downstream — and once the year ends, the conversion is irreversible (recharacterization was eliminated by the TCJA). Sizing the conversion to stay below the relevant tier requires modeling MAGI before clicking the conversion button.
MAGI for IRMAA — definition
MAGI for IRMAA is AGI plus tax-exempt interest (line 2a on Form 1040). It does not add back student loan interest, foreign earned income exclusion, or many other items that other MAGI definitions include.
Components that count toward MAGI for IRMAA:
- All taxable income (wages, interest, dividends, capital gains, pension, taxable Social Security)
- Roth conversion amount (in full)
- Required Minimum Distributions
- Tax-exempt municipal bond interest
Components that do not count toward MAGI for IRMAA:
- Qualified Charitable Distributions (excluded by definition)
- Roth IRA withdrawals (already taxed at conversion)
- Tax-free §121 home sale exclusion (the excluded portion)
- HSA distributions for qualified medical expenses
3. The 65-but-not-yet-Medicare gap
Retirees often turn 65 (Medicare eligibility) before the IRMAA implications of large conversions hit. The dangerous sequence:
| Year | Age | Action | Effect |
|---|---|---|---|
| 2024 | 62 | Retire early; income drops | — |
| 2026 | 64 | Convert $250K Traditional IRA to Roth | MAGI = $280K |
| 2027 | 65 | Enroll in Medicare 3 months before 65th birthday | — |
| 2028 | 66 | First IRMAA-affected year | $5,299 surcharge per spouse if MFJ — both spouses pay regardless of who triggered it |
For a couple, both spouses pay the same IRMAA tier surcharge in 2028 even though only one spouse’s MAGI pushed across the threshold (assuming MFJ filing). That doubles the effective cost of the conversion.
4. Bracket-aware sizing — the practical mechanic
The standard approach is to size each year’s conversion to fill a current tax bracket without crossing into the next IRMAA tier.
Worked example: filling the 22% bracket without crossing IRMAA tier 1
Tom (single, age 62, retired, no Medicare yet) has:
- $20,000 dividend income
- $0 other income
- 2026 standard deduction (single, age 62 — not yet 65+): $15,350
His taxable income before any conversion = $20,000 − $15,350 = $4,650.
- 12% bracket ends at $48,475 → room of $43,825 of conversion at 12%.
- 22% bracket ends at $103,350 → room of $98,700 of conversion at 12%/22%.
- IRMAA single tier 1 at MAGI = $109,000.
- Subtract his $20,000 dividend income → max conversion to stay at MAGI ≤ $109,000 is $89,000.
The bracket-filling conversion is $89,000 — sized by IRMAA, not by tax bracket. Federal tax on the $89,000 conversion: roughly $14,000 (12% + 22% blended). Each year through age 64, Tom can repeat the same size, locking in 12-22% federal cost on what would otherwise be future 22%+ RMD distributions.
If Tom instead converted $90,000, MAGI = $110,000 — over the IRMAA tier by $1,000. His 2028 Medicare premium surcharge = $1,054.80. He pays $1,054.80 to save the federal tax on his last $1,000 of conversion ($220 at 22%) — a net loss of $834.80.
The “fill to the cliff” rule
Always size each year’s conversion so MAGI lands $1,000 to $3,000 below the next IRMAA tier — never at the tier. Tax software margins, year-end adjustments, and projected dividend reinvestments routinely push MAGI $500-$1,500 higher than initial projections.
5. Multi-year strategy: how aggressive in pre-Medicare years?
For a couple aged 62-64 (3 years before Medicare), the strategy is often:
- Year 1 (age 62): Larger conversion. No IRMAA exposure for 2 years. Fill to top of 24% bracket if state-tax planning supports.
- Year 2 (age 63): Larger conversion. Still no IRMAA. Last “free” year.
- Year 3 (age 64): First year with IRMAA implication (2-year look-back means age 64 MAGI determines age 66 IRMAA). Size to stay below relevant tier.
- Year 4+ (age 65 onward): Every year’s MAGI affects future IRMAA. Sizing tightens.
Crossing the IRMAA threshold in the no-Medicare years 62-63 carries no cost — the IRMAA only applies once enrolled in Medicare. This is sometimes called the “IRMAA-free window” and is among the highest-value 3-year planning periods in a typical retirement timeline.
6. The SSA-44 appeal — life-changing event reduction
After enrollment, IRMAA is recalculated annually based on the 2-year-prior return. But Social Security accepts an SSA-44 form to reduce IRMAA based on certain “life-changing events”:
- Marriage or divorce
- Death of a spouse
- Work stoppage or reduction (e.g., retirement)
- Loss of pension or income-producing property
- Settlement of employer pension
A Roth conversion is not a qualifying life-changing event. There is no SSA-44 escape hatch for a conversion-induced IRMAA cliff. Once 2026 MAGI is filed, 2028 IRMAA is locked.
The one nuance: if you retire in 2026 and your 2024 (look-back) MAGI was much higher than your current income, SSA-44 lets you certify the work-stoppage and use estimated 2026 MAGI for 2026 IRMAA purposes. This is the same form used by anyone retiring late in the calendar year.
7. State Medicaid-Medicare interaction
Most states with retiree-friendly tax policy (FL, TX, WA, NV, AK, WY, SD, TN, NH on interest/dividends, PA partially) have no state income tax on IRA distributions or Roth conversions. The IRMAA decision is therefore purely federal in those states.
In high-tax states (CA, NY, NJ, OR, MN, HI), a Roth conversion is taxed at both federal and state levels in the conversion year. The state tax adds to the cost-benefit but does not change the IRMAA mechanic.
A relocation to a no-income-tax state before a planned conversion is a separate strategy — see the State Income Tax Calculator for the per-state mechanics.
8. QCDs as an IRMAA defensive lever
For retirees already 70½+, a Qualified Charitable Distribution can keep MAGI below an IRMAA tier even when RMDs would otherwise push it across. The $108,000 QCD limit in 2026 is enough to satisfy the entire RMD for many retirees.
Strategy stacking:
- Convert in the 62-64 IRMAA-free window.
- After Medicare enrollment, defer remaining conversions and let RMDs begin.
- Use QCDs to satisfy RMDs while keeping MAGI below the relevant IRMAA tier.
This sequence converts the maximum balance in the no-IRMAA window, then uses QCDs to manage the IRMAA exposure on the remaining Traditional IRA balance.
9. Common mistakes
- Forgetting to add tax-exempt interest to MAGI. A retiree with $50K of municipal bond income has $50K more MAGI for IRMAA than they have AGI. This often pushes a conversion across a tier that the AGI-only model showed as safe.
- Underestimating year-end dividend reinvestment. Mutual fund capital-gain distributions in late December can add $5K-$15K to MAGI unexpectedly. Convert early in the year and leave a margin.
- Filing Married Filing Separately to avoid IRMAA. MFS has even tighter IRMAA brackets and almost always increases total tax. The strategy backfires.
- Treating IRMAA as a tax. IRMAA is reported on Form 1040 but is technically a Medicare premium surcharge — not deductible against any tax credit and not refundable.
- Crossing on $1. The cliff structure means very tight planning is needed. Always size to $1,000+ below the threshold.