Why Medicare Enrollment Changes the Roth Conversion Math
A Roth conversion before Medicare IRMAA is a strategy where retirees ages 60–64 convert traditional IRA funds to Roth accounts, paying income tax now to reduce future Medicare premium surcharges. The tradeoff is straightforward: higher taxable income in the conversion year versus lower Medicare Part B and Part D premiums for the rest of your life.
Before age 65, a Roth conversion only affects your current-year tax bill. After Medicare enrollment, the same conversion can trigger IRMAA surcharges that add $74 to $445.50 per month to Part B premiums for two years.1 This changes the calculation entirely.
The key insight is that Medicare uses a two-year lookback. Your 2025 Part B premium is based on your 2023 tax return MAGI. A conversion done at age 63 shows up in the premium calculation at age 65, when Medicare begins. This means the window between ages 60 and 64 is the last opportunity to convert without IRMAA consequences.
For a single filer, the first IRMAA threshold in 2025 is $106,000 MAGI.1 A client who stays under that threshold saves $1,052.40 per year in combined Part B and Part D surcharges. Over a 20-year retirement, that is $21,040 in avoided premium costs.
Understanding Your 2025–2026 IRMAA Thresholds and Surcharge Tiers
The 2025 IRMAA brackets for Medicare Part B are structured in five tiers based on MAGI:
| MAGI (Single) | MAGI (Married Joint) | Part B Monthly Surcharge | Part D Monthly Surcharge |
|---|---|---|---|
| $106,000 or less | $212,000 or less | $0 | $0 |
| $106,001–$133,000 | $212,001–$266,000 | $74.00 | $13.70 |
| $133,001–$167,000 | $266,001–$334,000 | $185.80 | $35.30 |
| $167,001–$200,000 | $334,001–$400,000 | $296.60 | $57.00 |
| Over $200,000 | Over $400,000 | $445.50 | $78.60 |
The Part D surcharge is added on top of the Part B amount. A client crossing the first threshold pays an extra $1,052.40 per year in combined surcharges. Crossing the second tier adds $2,653.20 per year.
These thresholds are not indexed to inflation in the same way as tax brackets. Advisors should apply a 2% to 3% annual growth rate to thresholds, consistent with historical Medicare cost trends, when modeling future years. Note: 2026 IRMAA thresholds have not yet been officially released by CMS.
The Two-Year IRMAA Recalculation Rule and How Conversions Spike It
IRMAA surcharges are recalculated every two years based on the most recent tax return available. For a client enrolling in Medicare at age 65 in 2025, the 2023 tax return determines the 2025 premium. The 2024 return determines the 2026 premium.
This creates a specific risk: a large Roth conversion in a single year can spike MAGI for two consecutive premium years. Suppose a client converts $50,000 in 2024. That income appears on the 2024 return, which sets the 2026 premium. If the client also had a high-income year in 2023, the 2025 premium is already elevated.
The solution is to spread conversions across multiple years. A client with $95,000 baseline MAGI can convert $10,000 per year for three years without crossing $106,000, for example, avoiding IRMAA entirely while still reducing the traditional IRA balance by $30,000. This phased approach keeps each lookback year under the threshold.
Building a Phased Conversion Schedule Between Ages 62 and 65
The optimal conversion schedule fills the gap between baseline income and the first IRMAA threshold each year. For a single filer with $60,000 in baseline MAGI, the maximum conversion is $46,000 per year to stay under the $106,000 threshold. For married filing jointly with $80,000 baseline, the maximum is $132,000 per year under the $212,000 threshold.
| Baseline MAGI | Filing Status | Max Annual Conversion | Total Over 3 Years |
|---|---|---|---|
| $60,000 | Single | $46,000 | $138,000 |
| $80,000 | Married Joint | $132,000 | $396,000 |
| $45,000 | Single | $61,000 | $183,000 |
The goal is to fill the 12% and 22% tax brackets without crossing the first IRMAA threshold in any lookback year. Advisors should build in a 5% to 10% buffer below each threshold to account for unexpected income like capital gains distributions or interest rate changes. Converting to exactly $211,999 leaves no margin for error.
Calculating the Break-Even: Tax Now vs. Lower IRMAA for Life
The break-even calculation compares the tax cost of Roth conversion before Medicare IRMAA triggers against the lifetime IRMAA savings. For a single filer with $60,000 in baseline income, converting $50,000 per year for three years costs 22% federal tax on $150,000 — $33,000 total. If that conversion keeps post-65 MAGI below $106,000, the client saves $1,052 per year in avoided surcharges.
At age 85, that is $21,040 in premium savings. The net cost of the conversion strategy is roughly $11,960, but the client also gains tax-free growth on the converted $150,000 and avoids NIIT on future RMDs.
Using the same scenario, $33,000 in tax divided by $1,052 annual savings equals 31.4 years — longer than most clients will live. The break-even improves when factoring in tax-free growth and reduced RMDs. A client who lives to 90 saves $26,300 in premiums, making the net cost $6,700 for $150,000 in tax-free assets.
How Social Security Claiming Age Interacts With Your Roth Strategy
Social Security benefits increase provisional income, which affects both the taxability of benefits and IRMAA thresholds. Roth conversions increase provisional income, which can push a portion of Social Security benefits from tax-free to 50% or 85% taxable.
A client claiming Social Security at 62 adds $24,000 to $36,000 per year in taxable income before Medicare begins, reducing the available conversion capacity under the IRMAA threshold. For a single filer with $30,000 in Social Security benefits and $60,000 in other income, provisional income is $105,000. Converting $10,000 pushes provisional income to $115,000, making 85% of Social Security benefits taxable instead of 50%.
The effective marginal rate on that $10,000 conversion jumps from 22% to 40.7% due to the Social Security tax torpedo. Advisors should model Social Security claiming age as a variable in the conversion schedule, not a fixed assumption.
Case Study: Client Scenario With Before-Medicare Conversion Analysis
Consider a hypothetical client scenario. Michael is a single filer, age 62, with $45,000 per year in pension income. His IRA balance is $800,000. His baseline MAGI is $45,000, well below the $106,000 first IRMAA threshold.
If Michael converts $60,000 per year from ages 62 to 64, he pays 22% federal tax on $180,000 total — $39,600. His IRA balance drops to $620,000, reducing future RMDs to $24,000 per year. Combined with pension income, his post-65 MAGI stays at $69,000, well below the $106,000 threshold.
The conversion cost of $39,600 saves him from potentially hitting the second IRMAA tier in later years, which would cost $1,052 per year. If he lives to 85, that is $21,040 in premium savings. The net cost of the conversion strategy is $18,560, but he also avoids NIIT on future RMDs and gains tax-free growth on the converted $180,000.
If Michael does nothing, his IRA grows to $1.2 million by age 73, producing RMDs of $47,000 per year. Combined with pension income, his MAGI hits $92,000, still under the first threshold. However, if he delays conversions until 66, his RMDs at 73 would be $55,000, pushing MAGI to $100,000 — dangerously close to the $106,000 threshold.
Common Mistakes Advisors Make When Modeling Roth Conversions for Medicare Clients
Many advisors model only Part B IRMAA and ignore Part D surcharges. The Part D surcharge adds $13.70 to $78.60 per month depending on the tier. Failing to include Part D in the model understates the true cost of crossing a threshold by 15% to 20%.
Using static thresholds is another common error. IRMAA thresholds are adjusted annually based on Medicare cost trends. A better approach is to apply a 2% to 3% annual growth rate to thresholds, consistent with historical Medicare cost trends, when modeling future years.
The Social Security tax torpedo is frequently overlooked. Roth conversions increase provisional income, which can push Social Security benefits into taxable territory. The effective marginal rate on a conversion can jump from 22% to 40.7% due to this interaction.
Converting too close to the threshold creates unnecessary risk. Converting to exactly $211,999 leaves no margin for error. A $500 capital gains distribution or interest rate change can push MAGI over the threshold, triggering a $1,052 surcharge for two years.
Your Next Step
Download the Smart Money After 60 Roth Conversion Calculator template and run three scenarios for your next client meeting: a single filer with $60,000 baseline, a married couple with $80,000 baseline, and a client with Social Security benefits already claimed. Map the conversion amounts against the 2025 IRMAA thresholds and calculate the break-even year for each scenario. Present the results as a side-by-side comparison showing tax cost versus lifetime premium savings.