How long does an IRMAA surcharge from a Roth conversion last?

One premium year, which is twelve months of premiums. Social Security redetermines the surcharge every year against the newest return the IRS has sent, so a conversion in 2026 raises 2028 premiums and nothing after that, provided 2027 income comes back down. There is no carryover and no true-up bill. Convert large amounts in consecutive years, though, and you get consecutive surcharge years.

Is the Medicare surcharge large enough to change whether I convert?

Usually not by itself, but it should change the amount. For a couple in the second joint bracket in 2026 the surcharge runs $2,296.80 for the year, and in the third it runs $5,769.60. Against a $200,000 conversion that is under 3% of the amount converted, which a lifetime of smaller required distributions can easily beat. The number that matters is the marginal one: the last $12,000 of a conversion that pushes you across a line can cost $3,472.80 on its own.

At what age do Roth conversions start affecting Medicare premiums?

The year you turn 63, if you enroll in Medicare at 65. Premiums for any year are set from the tax return two years earlier under 20 C.F.R. §418.1135, so the return for the year you turn 63 is the first one that can produce a surcharge. Conversions before that are outside the lookback entirely, which is why the early sixties are the cheapest conversion window most retirees get.

Does tax-exempt municipal bond interest count toward IRMAA?

Yes. The IRMAA definition of modified adjusted gross income at 42 U.S.C. §1395r(i)(4) is adjusted gross income increased by tax-exempt interest, so the interest reported on Form 1040 line 2a counts in full even though it is not taxable. A retiree with a large municipal portfolio can be pushed into a bracket by income that never shows up on the tax line of the return.

Can I have the tax withheld from the IRA to keep my conversion income lower?

No. Withholding out of the IRA does not reduce the distribution, it just sends part of it to the IRS instead of to the Roth, and the whole amount is still income for both tax and IRMAA. If you are under 59½ the withheld portion is also not converted, which makes it an early distribution subject to the 10% additional tax under §72(t). Pay the conversion tax from outside money.

The Journal / Retirement Tax

Roth Conversion Medicare Premium Surcharge: The Bill Comes Two Years Later.

By Ewan Morkel, EAJuly 25, 20268 min read

A Roth conversion is ordinary income, and Social Security counts it when it sets your Medicare Part B and Part D premiums two years later. For 2026 premiums the first joint threshold is $218,000, and crossing it by a dollar costs a married couple $2,296.80.

Senior couple reviewing expenses and making notes together

A retired couple in their late sixties spends the gap years between retirement and required minimum distributions moving traditional IRA money into a Roth. The income tax math looks clean: fill the 22% bracket, pay now, never pay again. Then two years later the Social Security deposit shrinks, because the Medicare premium withheld from it went up by a few hundred dollars a month for each of them. That is the Roth conversion Medicare premium surcharge, and it runs for a full twelve months.

The lookback

Why a conversion you made in 2024 sets your 2026 premium.

Social Security runs this surcharge, not the IRS, and it works off old data. Its formal name is the income-related monthly adjustment amount, or IRMAA. Under 20 C.F.R. §418.1135, Social Security uses the modified adjusted gross income the IRS reports for the tax year two years before the premium year. Your 2026 premiums come off your 2024 return. If that return is not available when premiums are set, Social Security temporarily uses the year three years prior and trues it up later. There is no way to opt into current-year income.

Modified adjusted gross income has its own definition here, at 42 U.S.C. §1395r(i)(4): adjusted gross income under §62, figured without regard to the exclusions in §§135, 911, 931, and 933, increased by tax-exempt interest. Two things follow from that. Municipal bond interest counts even though it is not taxable. And because the test stops at AGI, nothing below the line helps. Your standard deduction, your itemized deductions, and your charitable deduction all leave the number untouched.

A Roth conversion is a distribution from a traditional IRA that you do not roll back, so the converted amount is ordinary income on Form 1040 line 4b and sits inside AGI at full value. There is no exception for conversions, no averaging, no partial exclusion. Convert $100,000 and your IRMAA income for that year is $100,000 higher. One practical consequence: if you enroll in Medicare at 65, the first conversion year that can raise a premium is the year you turn 63.

The 2026 table

What the Roth conversion Medicare premium surcharge costs at each threshold.

The standard Part B premium for 2026 is $202.90 a month, with a $283 annual deductible, set in the notice CMS published in the Federal Register on November 19, 2025. Above the thresholds, Part B carries a surcharge and Part D carries a separate one, both driven by that same MAGI figure. Here is the full 2026 table, measured against 2024 income.

$218,000 or less joint, $109,000 or less single: no surcharge, and Part B is $202.90 a month.
Over $218,000 to $274,000 joint, over $109,000 to $137,000 single: Part B $284.10, plus $14.50 for Part D.
Over $274,000 to $342,000 joint, over $137,000 to $171,000 single: Part B $405.80, plus $37.50 for Part D.
Over $342,000 to $410,000 joint, over $171,000 to $205,000 single: Part B $527.50, plus $60.40 for Part D.
Over $410,000 to $750,000 joint, over $205,000 to $500,000 single: Part B $649.20, plus $83.30 for Part D.
$750,000 or more joint, $500,000 or more single: Part B $689.90, plus $91.00 for Part D.

Three features make this bite harder than the table suggests. It is a cliff: one dollar over a threshold triggers the whole tier, with no phase-in to soften the crossing. It is charged per person, so a couple with both spouses on Medicare pays it twice. And the hold-harmless rule in 42 U.S.C. §1395r(f), which keeps a Social Security check from shrinking when premiums rise, does not apply to anyone paying IRMAA. CMS estimates about 8% of Part B enrollees land in that group.

A retired couple, both on Medicare, converting in 2024 for 2026 premiums.

Pension, dividends, and taxable Social Security (MAGI before converting): $205,000
Roth conversion: $80,000
2024 MAGI as Social Security measures it: $285,000
2026 joint bracket it lands in: Over $274,000 to $342,000
Part B surcharge, per spouse, per month: $202.90
Part D surcharge, per spouse, per month: $37.50
2026 Medicare surcharge, two spouses, twelve months: $5,769.60
Same couple converting $68,000 instead (MAGI $273,000): $2,296.80
Cost of the last $12,000 of conversion: $3,472.80

Tax year 2024 income, 2026 premium year, both spouses enrolled in Part B and Part D. Surcharge amounts are the 2026 figures CMS released November 14, 2025. The third-bracket Part B surcharge happens to equal the $202.90 standard premium, so the Part B bill is $405.80 per spouse. Combined with Part D, the larger conversion costs $240.40 per spouse per month; the smaller one stops in the second bracket at $95.70. Income tax on the conversion is separate and not shown. Trimming the conversion by $12,000 saves $3,472.80 of surcharge, which is 28.9% of that slice before any income tax is counted.

The appeal

Form SSA-44 will not undo a conversion.

Clients ask about appealing, and there is a form, and it does not help here. Form SSA-44 asks Social Security to use a more recent tax year in place of the two-year-old one, but only after a major life-changing event, and 20 C.F.R. §418.1205 lists them: the death of your spouse, marriage, divorce or annulment, you or your spouse stopping work or cutting hours, loss of income-producing property, loss or reduction of pension income, and an employer settlement payment tied to that employer's closure, bankruptcy, or reorganization. The list is exclusive.

A Roth conversion is not on it. Neither is a capital gain, the sale of a business, an inherited IRA distribution, or an unusually large required distribution. Social Security treats those as income you chose to recognize. What does work is a data problem rather than an income problem: if Social Security used the wrong figure, or you amended the return that set the premium, 20 C.F.R. §418.1150 lets you hand over the amended return within three years of the close of that tax year, with the IRS letter or a transcript, and the premium is corrected retroactively.

The planning

Convert up to the threshold, not through it.

The only real lever is the size of the conversion, and you pull it in the year you convert. Converting up to a threshold instead of through it means projecting the whole return rather than the conversion alone, because everything in AGI counts: capital gains from rebalancing, municipal bond interest, the taxable share of Social Security that the conversion itself pushes up, and, once you turn 73, the required distribution you have to take before you convert anything.

Filing separately is not a workaround. Married filing separately starts surcharging at $109,000, the same place a single filer starts, and then jumps straight to the fourth tier at $649.20 for Part B plus $83.30 for Part D. Two spouses filing separately in that range usually pay more between them than they would have paid jointly.

None of this means the surcharge should shrink every conversion. A one-year cost of $5,769.60 against a $200,000 conversion is 2.9% of the amount converted, and it buys a permanently smaller traditional IRA, smaller required distributions for life, and a smaller bill for whichever spouse eventually files as a single. I price both before deciding. The surcharge changes the plan at the margin, when the last $10,000 or $20,000 is the piece that crosses the line. That slice is the expensive one, and trimming it costs almost nothing.

One caveat on the figures above. A conversion done in 2026 sets 2028 premiums, and CMS will not publish the 2028 brackets until the fall of 2027. The thresholds are indexed and drift up each year, with one exception: the top tier has been frozen at $500,000 and $750,000 since the Bipartisan Budget Act of 2018 and is not scheduled to move until 2028. Plan against the published table and leave a cushion under the line. If you are past 70½ and give to charity, a qualified charitable distribution never enters AGI at all, so it is one of the few moves that lowers IRMAA income directly.