The Roth Conversion IRMAA Trap

How a Smart Tax Move Can Cost You $5,000 in Medicare Premiums

Crossing an IRMAA income threshold by even one dollar can trigger thousands in extra Medicare Part B costs two years later. Here’s the math, the timing window, and how to convert without walking into this trap.

You run the numbers on a Roth conversion. Your tax bracket works out. You convert $150,000 from your traditional IRA, pay the taxes, and feel good about reducing future required minimum distributions. Smart move.

Two years later, your Medicare Part B premium is $405.80 a month instead of $202.90. That’s an extra $203 per month, per person, $4,872 per year, per couple, and it keeps hitting as long as that conversion year’s income shows up in your record. The math you ran in 2026 is now costing you in 2028.

This is the Roth conversion IRMAA Medicare premium problem, and it catches a lot of high-net-worth pre-retirees who optimized for federal income tax without modeling Medicare costs at all. The good news: it’s entirely avoidable if you know where the income cliffs are and when to convert.

What IRMAA Actually Is (and Why the Two-Year Lag Blindsides People)

IRMAA stands for Income-Related Monthly Adjustment Amount. It’s a Medicare premium surcharge that applies to higher-income beneficiaries, and it’s assessed based on your modified adjusted gross income from two years prior, not your current income.

So your 2026 income determines your 2028 Medicare premiums. Your 2025 income is already locked in for 2027. That two-year lookback is why this problem sneaks up on people: you make a financial decision today and the cost shows up two years from now, often when you’ve forgotten about the connection entirely.

In 2026, the standard Medicare Part B premium is $202.90 per month, a 9.7% increase from $185.00 in 2025. That’s more than three times the 2.8% Social Security COLA announced for 2026. For retirees relying on that COLA to keep pace with costs, the premium increase alone eats a significant share of it.

The 2026 IRMAA Brackets: Where the Cliffs Are

Medicare Part B IRMAA surcharges kick in at five income tiers above the standard threshold. These are the 2026 numbers confirmed by CMS, based on your 2024 tax return:

Individual MAGI	Joint MAGI	Monthly Surcharge	Total Part B Premium	Annual Cost (per person)
Up to $109,000	Up to $218,000	$0	$202.90	$2,434.80
$109,001–$137,000	$218,001–$274,000	$81.20	$284.10	$3,409.20
$137,001–$171,000	$274,001–$342,000	$202.90	$405.80	$4,869.60
$171,001–$205,000	$342,001–$410,000	$324.60	$527.50	$6,330.00
$205,001–$499,999	$410,001–$749,999	$446.30	$649.20	$7,790.40
$500,000+	$750,000+	$487.00	$689.90	$8,278.80

The highlighted first surcharge tier is the one most people stumble into. A single dollar over $109,000 (individual) or $218,000 (joint) adds $81.20 per month to your Part B premium. That’s $974.40 per year, per person, or $1,948.80 per year for a couple, triggered by one extra dollar of income.

The $150,000 Conversion Scenario: What the Math Actually Looks Like

Here’s a concrete case. A married couple, both 63, has $1.4 million in traditional IRAs. Their retirement income consists of Social Security and a small pension, putting their MAGI at roughly $195,000 in a typical year. They decide to convert $150,000 to Roth in 2026 to reduce future RMDs. Their 2026 MAGI jumps to $345,000.

In 2028, Medicare receives their 2026 tax return and sets premiums accordingly. Their MAGI of $345,000 puts them in the Tier 3 IRMAA bracket ($342,001–$410,000 joint). Each spouse’s monthly Part B premium is now $527.50 instead of $202.90, a difference of $324.60 per person per month.

For the couple, that’s $649.20 in extra Part B premiums every month, or $7,790.40 for the year. Add the Part D IRMAA surcharge, which runs $85.80 to $86.90 per person per month at this income tier, and you’re looking at over $9,800 in additional Medicare costs for 2028 alone.

If the conversion also pushes them into Tier 2 in 2029 (because the income appears on 2027 returns while they’re still managing other income), the hit compounds across multiple years.

The Two-Year Window That Changes Everything: Ages 60–63

Here’s where the planning opportunity is hiding. If you turn 65 in 2028, Medicare uses your 2026 MAGI to set your initial premiums. Work back two years from your Medicare start date, and you identify the last conversion year that doesn’t affect Medicare bills at all.

For someone who turns 65 in 2028, conversions done in 2025 or earlier affect 2027 Medicare premiums, which they won’t be enrolled in yet. Conversions in 2026 and 2027 affect 2028 and 2029 premiums, which they will pay.

But for someone still 60, 61, or 62, they have years of runway to convert aggressively before the IRMAA lookback catches up to them. A 62-year-old in 2026 has, effectively, a clear window to do large conversions without a Medicare cost attached, because they won’t be on Medicare until 2029 at the earliest, by which time the 2026 return will already be two tax years behind the initial enrollment assessment.

The practical upshot: ages 60–63 are often the highest-value Roth conversion years for high-income retirees, not because the tax brackets are friendlier, but because the Medicare exposure is zero or minimal. Once you’re at 63 or 64, every large conversion has a two-year tail that lands squarely in your Medicare years.

How to Calculate Your Safe Conversion Ceiling

The goal is to find the conversion amount that maximizes tax efficiency without crossing the next IRMAA tier. This requires knowing three numbers:

1. Your projected MAGI without any conversion. Add up all expected income sources for the year: Social Security (85% may be taxable), pension, withdrawals, dividends, capital gains. Don’t forget required minimum distributions if you’re already taking them.

2. The nearest IRMAA threshold above your current MAGI. For a married couple with $195,000 in base MAGI, the next cliff is $218,000. That gives them a $23,000 conversion ceiling before they cross into the first surcharge tier.

3. The tax cost versus Medicare cost tradeoff. Sometimes it makes sense to deliberately cross a tier if the tax benefit of converting is large enough. But you have to model the Medicare surcharge as a real dollar cost on the other side of the equation.

Questions to Work Through With Your Advisor

1. What is my projected MAGI this year, including all income sources, before any conversion?
2. How many dollars separate me from the next IRMAA bracket? What’s my safe conversion ceiling?
3. Am I still in the pre-Medicare window (under 63), and have we modeled conversions accordingly?
4. What are my projected RMDs starting at age 73 or 75, and how does today’s conversion reduce that future obligation?
5. If I cross a tier, have we calculated the net benefit after Medicare surcharges, not just federal income tax savings?
6. Does my spouse’s Medicare enrollment create a separate IRMAA exposure if we file jointly?
7. Have we accounted for Part D IRMAA surcharges, not just Part B?

IRMAA Red Flags in Common Roth Conversion Advice

• The advice is to “fill up your tax bracket” without any mention of IRMAA. Filling your 22% or 24% bracket may still push you over an IRMAA threshold that adds an effective 5–10% marginal surcharge on top.
• The conversion plan is based on income tax software projections that don’t include Medicare cost modeling. Most tax software doesn’t flag IRMAA exposure automatically.
• Your advisor is recommending the same conversion amount every year without checking the current-year IRMAA thresholds, which shift annually.
• The analysis assumes your MAGI is only your ordinary income. Capital gains, taxable Social Security, and investment income all count toward the IRMAA calculation.
• No one has discussed a IRMAA appeal. If your income in the lookback year was unusually high due to a one-time event (a business sale, a single large conversion), you may be eligible to appeal the surcharge using a more recent tax return.

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The Bottom Line

Roth conversions are one of the best planning tools available to pre-retirees with large traditional IRA balances. But the tax bracket calculation is only half the analysis. The Roth conversion IRMAA Medicare premium problem is real, and it’s measurable, and it’s almost entirely avoidable with the right modeling.

The number to find isn’t “how much can I convert before I hit the 24% bracket.” It’s “how much can I convert before I hit the next IRMAA cliff,” and then weigh the tax savings against the Medicare cost if you cross it anyway.

Do that calculation every year, starting from a full MAGI projection, and you’ll convert the right amount instead of the most amount. For someone sitting on $1.4 million in an IRA at age 62, that’s probably the highest-value financial planning conversation they’ll have this decade.

This content is for informational purposes only and does not constitute financial, tax, or legal advice. Consult a qualified fiduciary advisor before making significant financial decisions.