Roth conversion IRMAA bracket planning is the practice of timing and sizing conversions from a traditional IRA or 401(k) into a Roth account so that the extra ordinary income does not push your modified adjusted gross income (MAGI) over an Income-Related Monthly Adjustment Amount (IRMAA) threshold. Done well, it can save a retiree thousands of dollars per year in Medicare surcharges; done carelessly, a single dollar over a threshold can cost more than the tax benefit of the conversion itself.
The Direct Answer
Also worth reading: How do I appeal a Medicare Part D IRMAA surcharge in 2026, and what's the best strategy for winning? · What are the Medicare Special Enrollment Period rules for 2026, and when can I change my Medicare plan outside Open Enrollment? · What should I do about Medicare Advantage plan discontinuations in 2027?
For 2026, your Medicare premiums are determined by the MAGI reported on your 2024 tax return, because IRMAA operates on a two-year lookback. If you file as single and your 2024 MAGI was $106,000 or less ($212,000 married filing jointly), you pay the standard 2026 Part B premium of roughly $203 per month per person plus the standard Part D premium. Cross the first threshold and both spouses' Part B and Part D premiums rise through surcharges that are not prorated — one dollar over the line triggers the full bracket penalty for the entire year.
The planning task is therefore straightforward in concept but unforgiving in execution: before each year-end, project your MAGI including any planned Roth conversion amount, identify the highest IRMAA threshold you can stay under without sacrificing too much of your conversion goal, and size the conversion to land safely below that line. Many planners recommend leaving a buffer of several thousand dollars below the threshold because MAGI can shift after the fact — a corrected 1099, a capital gain distribution from a mutual fund in December, or interest income you did not anticipate can all push you over after the conversion is already locked in.
How IRMAA Actually Works in 2026
IRMAA is a surcharge added to Medicare Part B and Part D premiums for higher-income beneficiaries. It is calculated by the Social Security Administration using the most recent tax return available — for calendar year 2026, that means your 2024 return. There are five income tiers above the standard tier, and the surcharge amounts step up at each tier for both Part B and Part D.
The 2026 single-filer thresholds begin at $106,000 of MAGI, then rise to $133,000, $167,000, $200,000, and finally $500,000. For joint filers the tiers double: $212,000, $266,000, $334,000, $400,000, and $750,000. At the top tier, a married couple can pay combined Part B and D surcharges exceeding $10,000 per year over the standard amounts. Note that these surcharges apply per person, so a married couple where both spouses are on Medicare pays double the individual surcharge — this is why crossing a threshold is roughly twice as expensive for couples as the headline numbers suggest.
MAGI for IRMAA purposes is your adjusted gross income plus tax-exempt interest (such as municipal bond income). A Roth conversion adds its full amount to AGI because converted dollars are taxed as ordinary income in the year of conversion. This is the mechanism that makes conversion planning and IRMAA planning inseparable: every dollar you convert moves you up the income ladder toward the next cliff.
Why One Dollar Over a Threshold Costs So Much
The cliffs are absolute. If a single filer's MAGI lands at $106,001 instead of $106,000, they pay the entire first-tier surcharge for all twelve months of 2026 — there is no phase-in. Depending on the tier, the annual penalty ranges from a few hundred dollars at the lowest tier to well over $2,000 per person per year at the top tiers, and married couples on Medicare face double that. Commentators like Wes Moss have popularized the point that being one dollar over the wrong line can cost a retiree up to $4,000 a year, and the math supports it once both spouses' Part B and D surcharges are counted.
This cliff structure changes the risk calculus of a Roth conversion. A conversion that saves you 22% in future required minimum distribution taxes but accidentally triggers a two-year IRMAA penalty may be a net loss, especially if you were only slightly over the threshold. Laurence Kotlikoff has been blunt about this: conversion strategies built on simplistic rules of thumb — 'fill up the 22% bracket' or 'convert until the marginal rate hits X%' — can destroy value when they ignore IRMAA cliffs, taxation of Social Security benefits, and ACA subsidy interactions. Any serious plan models the full picture, not just the tax bracket.
Practical Steps for Sizing Your Conversion
Start by projecting your 2026 MAGI without any conversion. Include wages if you are still working, taxable investment income, dividends, capital gains, self-employment income, traditional IRA distributions, pension payments, and half of your Social Security benefits (the taxable portion). Add tax-exempt interest back in. This baseline tells you how much room remains under each IRMAA threshold.
Next, decide which threshold is your target. If your baseline MAGI is $95,000 as a single filer, you have about $11,000 of headroom under the first cliff — minus a safety buffer. Most practitioners suggest holding back $3,000 to $5,000, or more if you hold actively managed mutual funds that make unpredictable December capital gains distributions. Then compare the conversion amount that fits under the threshold against the amount that would fill the current federal tax bracket (for 2026, the 22% bracket for singles runs to roughly $206,700 of taxable income) and ask whether waiting a year, splitting the conversion across two years, or accepting a small IRMAA hit produces the better lifetime outcome.
Finally, execute conversions early enough in the year to allow recharacterization-free adjustments — remember that since 2018, Roth conversions cannot be undone, so precision matters. Many planners do a preliminary conversion in January or February, then a top-up in November or early December once dividend and gain figures are nearly final. Waiting until late December leaves no room to react to surprises.
Comparison: Conversion Strategies Under IRMAA Constraints
| Feature | Fill-the-Bracket Conversion | Threshold-Limited Conversion | Multi-Year Staged Conversion |
|---|---|---|---|
| Typical annual amount | Up to top of 22%/24% bracket | Only what fits under chosen IRMAA cliff | Smaller amounts spread over 3–8 years |
| IRMAA risk | High — often crosses multiple cliffs | Low if buffer maintained | Very low |
| Tax paid now | Highest | Moderate | Lowest per year |
| Best for | Large pre-tax balances, short life expectancy, high other income anyway | Retirees within ~$50K of a cliff | Retirees age 63–72 with moderate balances |
| Key danger | Two-year IRMAA surcharges erase savings | Under-converting leaves large RMDs later | Market growth outpaces conversions |
| Complexity | Low | Moderate — requires precise MAGI tracking | High — needs annual review |
Common Mistakes That Trigger Surprise Surcharges
The most frequent error is forgetting the two-year lookback. People convert in 2026 believing the IRMAA impact applies to 2026 premiums; in fact, their 2026 conversion will drive their 2028 premiums. Planning must always run two years ahead of the premium year you care about.
Second is ignoring capital gains outside the conversion. Selling appreciated stock in a taxable brokerage account, taking a large qualified dividend, or receiving a mutual fund's year-end distribution all add to MAGI. A conversion sized to the last dollar of headroom with no accounting for these items is a coin flip. Third is misunderstanding life-changing events: if your income drops due to retirement, divorce, or death of a spouse, you can file Form SSA-44 to request reconsideration of the surcharge based on current-year income rather than the lookback year. Many retirees who retired mid-cycle never file this form and overpay for years. Fourth is forgetting that IRMAA applies to Part D as well as Part B, and that the surcharge is added to whatever standalone drug plan or Medicare Advantage premium you pay — people who switch plans sometimes assume the surcharge disappears; it does not.
Fifth, couples where only one spouse has begun Medicare often miscalculate: the working spouse's income still counts toward the covered spouse's MAGI, and when the second spouse enrolls, both become subject to the couple's combined-income tier simultaneously.
When to Act and How AI Tools Change the Math
The ideal window for aggressive conversion planning is between retirement and age 73, when RMDs begin — ideally starting at 63, because the years before Medicare enrollment at 65 carry no IRMAA risk at all, making them the cheapest years to convert. Every year you delay, RMDs grow, Social Security begins adding taxable income, and the remaining pre-Medicare window shrinks.
This is also where modern tools earn their keep. Traditional advisors often run one or two static scenarios; simulation-based planners and AI-assisted brokers can model hundreds of conversion paths against IRMAA cliffs, Social Security taxation phases, ACA subsidies for pre-65 years, and state taxes simultaneously. An AI insurance broker platform can flag, for example, that converting $18,000 instead of $25,000 keeps you under the $106,000 cliff while still filling most of your remaining 12% bracket capacity — a trade-off easy to miss by hand. That said, treat any tool's output as a model, not gospel: assumptions about returns, health costs, and longevity dominate the result, and Kotlikoff's critique of 'rules of dumb' applies to software defaults as much as to human advisors. Verify the tool accounts for the two-year IRMAA lookback explicitly; many do not.
Cost-Benefit Reality Check
Be honest about whether conversion planning is worth the effort for your situation. If your total pre-tax balance is under roughly $150,000, projected RMDs will likely keep you below the first IRMAA threshold anyway, and elaborate planning adds little. If your baseline income already exceeds the top tier, incremental conversions change nothing on the IRMAA front and you should optimize purely on tax brackets. The planning sweet spot is households with $300,000 to $2 million in pre-tax accounts whose baseline MAGI sits within striking distance of one or two cliffs — precisely the group where a $1,000 sizing error costs real money.
Also weigh the non-IRMAA benefits honestly: Roth dollars escape RMDs entirely (for the original owner), provide tax-free inheritance for non-spouse heirs subject to the 10-year rule, and hedge against future tax increases. These benefits are real but probabilistic; the IRMAA penalty is certain and immediate. A defensible plan quantifies both sides rather than assuming conversion is automatically correct.
Bottom Line
Roth conversion IRMAA bracket planning in 2026 comes down to three disciplines: know your exact 2026 thresholds ($106,000/$133,000/$167,000/$200,000/$500,000 single; doubled for joint), always plan two years ahead of the premium year, and leave a buffer below every cliff you approach. Size conversions to the gap between your projected MAGI and your target threshold, execute early in the year with a December top-up, and use Form SSA-44 if a qualifying life event drops your income. Model the whole system — brackets, Social Security taxation, and IRMAA together — rather than optimizing any single variable, and skip aggressive conversions entirely if your balances are small enough that RMDs will never threaten a threshold.