6 Roth Conversion Traps Retirees Are Missing in 2026 (And How to Avoid Them)
You’ve been converting. Every fall you run the numbers, fill up the bracket, move a chunk from the traditional IRA to the Roth, and call it good. It’s worked for years. The problem is, the tax code you were filling that bracket against changed substantially in July 2025, and most retirees haven’t updated their math.
The One Big Beautiful Bill Act (OBBBA) introduced a new $6,000 senior deduction per person for those 65 and older. Sounds great. But it phases out sharply between $150,000 and $250,000 MAGI for joint filers, and Roth conversion income counts toward that number. That means a $100,000 Roth conversion can wipe out $12,000 in combined deductions for a couple, costing you thousands more than the bracket rate alone would suggest.
Layer in IRMAA’s two-year lookback on Medicare surcharges and the Social Security income inclusion thresholds, and the old “fill the 22% bracket” conversion playbook is genuinely broken. Here’s what’s changed, where the landmines are, and how to size a smarter conversion for 2026.
The 2026 Roth conversion trap is this: a new $6,000-per-person senior deduction under the OBBBA phases out between $150,000 and $250,000 MAGI for married couples, and Roth conversion income counts toward that threshold. A $100,000 conversion can eliminate a couple’s full $12,000 combined deduction, raising the effective tax rate on that conversion well above the stated bracket rate. Combined with IRMAA’s Medicare surcharge cliffs and Social Security taxation, the right conversion amount in 2026 is almost certainly smaller than it used to be. The new sweet spots: converting before age 65 (pre-IRMAA), staying below $150,000 MAGI for joint filers if you want to preserve the full senior deduction, or deliberately planning a single larger conversion in one year to “sacrifice” the deduction once and protect it for subsequent years.
6 Traps to Know Before You Convert
1
The Senior Deduction Phase-Out Is Steeper Than It Looks
The new $6,000 senior deduction under the OBBBA, available to taxpayers 65 or older for tax years 2025 through 2028, sounds like a straightforward win. For a married couple where both spouses are 65 or older, that’s $12,000 off taxable income. Not small.
But it starts phasing out the moment your MAGI exceeds $150,000 on a joint return. For every dollar you earn above that threshold, you lose $0.06 of the combined deduction. The full $12,000 is gone by $250,000 MAGI. A $100,000 Roth conversion that pushes a couple from $150,000 to $250,000 doesn’t just add $100,000 to taxable income, it removes another $12,000 in deductions at the same time, effectively taxing you on $112,000.
Fidelity ran this exact scenario: a married couple at $150,000 pension income doing a $100,000 conversion loses their entire $12,000 senior deduction and pays an additional $2,856 in taxes just from that deduction wipeout, not counting the bracket cost of the conversion itself.
Model your effective tax rate on the conversion, not just the marginal bracket rate. The real cost of converting across the $150,000–$250,000 band is higher than 22% or 24%.
Source: Fidelity Wealth Management, January 2026
2
IRMAA Isn’t a Tax, It’s a Cliff, and It Has a Two-Year Memory
Most people know that Medicare surcharges exist. Far fewer understand that they’re based on income from two years ago, and that crossing a threshold by a single dollar triggers the full surcharge. This isn’t a gradual tax; it’s a cliff.
For 2026, IRMAA applies to Medicare enrollees whose 2024 MAGI exceeded $109,000 (single) or $218,000 (joint). A couple just over the first joint threshold pays an extra $81.20 per person per month for Part B alone, $1,948.80 per year for both, plus Part D surcharges. The highest bracket adds $487.00 per person per month for Part B.
What this means practically: a Roth conversion you do in 2026 doesn’t affect your 2026 Medicare costs. It affects your 2028 costs. That two-year lag sounds like a cushion, but it’s actually a planning liability, you have to model income two years forward, not just this year.
| 2024 MAGI (Joint) | Part B Surcharge/mo | Part D Surcharge/mo | Annual Add’l Cost (both) |
|---|---|---|---|
| Up to $218,000 | $0 | $0 | $0 |
| $218,001–$274,000 | $81.20 | $14.50 | ~$2,328 |
| $274,001–$342,000 | $202.90 | $37.50 | ~$5,767 |
| $342,001–$410,000 | $324.60 | $60.40 | ~$9,241 |
| $410,001–$750,000 | $446.30 | $83.30 | ~$12,713 |
Avoid This
Don’t model IRMAA exposure for just the current year. Run a two-year forward income projection before sizing any conversion.
Source: Kiplinger, 2026 IRMAA Brackets and Surcharges
3
The “Fill the Bracket” Playbook Now Has Hidden Costs at 22% and 24%
The classic Roth strategy was simple: find the top of your current tax bracket, convert just enough to fill it, and stop. At 22% or 24%, the math usually beat future rates. That logic still holds in the abstract, but the bracket alone no longer tells you the full story.
In 2026, a married couple claiming the senior deduction who converts across the $150,000 MAGI threshold faces a de facto surtax. Walkner Condon’s analysis puts it plainly: you’re not just paying the bracket rate on the converted amount, you’re paying the bracket rate plus an effective 6% additional tax for every dollar of senior deduction you lose. Depending on your conversion size, the blended effective rate on that incremental income can run several points above the stated bracket.
The 2026 standard deduction for married filing jointly is $32,200, per the IRS. Add the two age-65+ additional standard deduction amounts ($1,650 per qualifying spouse) and the full $12,000 senior deduction, and a couple’s total deductions before income can reach roughly $47,500. A Roth conversion that doesn’t push MAGI past $150,000 preserves all of it. One that goes to $200,000 loses $3,000 of the senior deduction. One that goes to $250,000 loses all $12,000.
Run the conversion math from the deduction side, not just the bracket side. The question isn’t “what bracket am I filling?” It’s “what does my total taxable income look like after all deductions at each conversion level?”
Sources: IRS, 2026 Tax Inflation Adjustments; Walkner Condon Financial Advisors, December 2025
“A $100,000 Roth conversion that wipes out $12,000 in senior deductions effectively taxes you on $112,000, at your marginal rate.”
4
Roth Conversions Can Push More of Your Social Security Into Tax
Social Security benefits are partially taxable once your “combined income”, adjusted gross income plus nontaxable interest plus half your Social Security benefit, exceeds certain thresholds. Up to 85% of your Social Security benefits can be included in taxable income once combined income tops $44,000 for joint filers.
Because Roth conversion income is included in AGI, a meaningful conversion can take a retiree who’s taxing, say, 50% of their Social Security and push them to the 85% inclusion level. That’s not a tax on the conversion alone, it’s an effective tax on Social Security income that was otherwise partially excluded. For a couple receiving $40,000 annually in Social Security, moving from 50% to 85% inclusion adds $14,000 of previously sheltered income back into the taxable column.
This is one of the less-discussed interaction effects, but it can be material. It’s also invisible in a simple “what bracket am I filling” calculation.
What this means for you
Factor your Social Security inclusion rate into the conversion model. The marginal cost of a dollar of Roth conversion income is not always one dollar, it can be meaningfully more once Social Security taxation is recalculated.
Source: Social Security Administration, Benefits Planner: Income Taxes and Your Social Security Benefits
5
Ages 60–64 May Be the Best Conversion Window You Have Left
Here’s the counterpoint: if you’re 60 to 64 and not yet on Medicare, you’re in a potentially excellent position to convert. IRMAA doesn’t apply. The senior deduction hasn’t kicked in yet, so there’s no phase-out trap to navigate. You’re often in a lower-income year than you’ll be at 65 and beyond, when RMDs, Social Security, and Medicare all arrive at roughly the same time.
The retirement income valley, those years between leaving work and starting required minimum distributions at age 73, has long been favored for conversions. But the valley is narrower than it used to be. The OBBBA now means that once you turn 65, every conversion dollar above $150,000 MAGI is operating in a deduction phase-out zone. Converting in your early 60s sidesteps that problem entirely.
Advisors increasingly model conversion activity as “pre-Medicare” and “post-Medicare” with very different sizing logic for each phase. Pre-Medicare conversions can often be larger. Post-Medicare conversions need to respect IRMAA cliffs and the senior deduction threshold simultaneously.
Consider This
If you’re between 60 and 64 with substantial traditional IRA assets, this window may be the most favorable conversion opportunity in the current tax code. The math is worth running now.
Source: Walkner Condon Financial Advisors, December 2025; Fidelity Wealth Management, January 2026
6
Smaller or Timed Conversions Can Preserve More Than One Benefit
The instinct after reading all of the above might be to stop converting altogether. That’s probably too conservative, the case for Roth assets still holds, particularly for those with large traditional IRAs facing significant future RMDs and heirs in higher tax brackets. But the size and timing of conversions need a rethink.
The strategies advisors are using in 2026: partial annual conversions sized to stay below the $150,000 MAGI senior deduction threshold; a deliberate “sacrifice year” strategy where a couple accepts one year of full deduction loss in exchange for a larger conversion that reduces future RMD pressure; and Qualified Charitable Distributions (QCDs), which allow IRA assets to go directly to charity without flowing through MAGI, preserving both the senior deduction and IRMAA positioning simultaneously.
One Bogleheads poster in an active thread on this exact issue described cutting a planned $100,000 conversion to $34,000 after modeling the senior deduction cliff. That’s a 66% reduction in conversion size to preserve a $12,000 deduction, which tells you how material the phase-out can be at certain income levels.
There’s no universal answer here. This is where it gets genuinely individual, and where a spreadsheet doesn’t substitute for a full income projection.
Key Approach
Consider QCDs as a complement to, not replacement, for Roth conversions. Donors who are charitably inclined can use QCDs to reduce IRA balances and future RMDs without triggering MAGI-sensitive phase-outs.
Sources: Fidelity Wealth Management, January 2026; Bogleheads Forum Thread, started July 2025
Common Questions
Does Roth conversion income count toward the new 2026 senior deduction phase-out?
Yes. Roth conversion income is included in MAGI, which is the figure used to calculate the senior deduction phase-out under the OBBBA. For married couples filing jointly, the combined $12,000 senior deduction begins phasing out at $150,000 MAGI and disappears entirely at $250,000. For every dollar above $150,000, the deduction shrinks by $0.06, so a couple converting $100,000 above that threshold loses the full $12,000 benefit.
What are the 2026 IRMAA thresholds for Medicare surcharges?
For 2026, Medicare Part B surcharges apply to enrollees whose 2024 MAGI exceeded $109,000 (single) or $218,000 (joint). Surcharges for Part B range from $81.20 to $487.00 per person per month; Part D surcharges run $14.50 to $91.00 per month. The base 2026 Part B premium is $202.90 per month. Because IRMAA uses a two-year lookback, your 2026 premium is determined by 2024 income, and your 2026 Roth conversion affects 2028 Medicare costs.
When is the best time to do Roth conversions to avoid IRMAA?
The window between retirement and Medicare eligibility at age 65 is often ideal, since IRMAA doesn’t yet apply. Pre-Medicare years (typically ages 60–64) allow larger conversions without triggering surcharges. Once you’re enrolled in Medicare, conversions should be sized to stay below IRMAA thresholds using a two-years-forward income projection, a 2026 conversion affects 2028 Medicare premiums.
Can I do a partial Roth conversion to preserve the senior deduction?
Yes, and this is one of the primary strategies advisors are using in 2026. Rather than a single large conversion, spreading smaller annual conversions lets you control MAGI, keeping it below the $150,000 joint phase-out threshold for the senior deduction and the $218,000 first IRMAA bracket. The tradeoff is slower conversion pace; the benefit is preserving several thousand dollars in deductions annually.
Does the new 2026 senior deduction apply if you itemize?
Yes. The $6,000 senior deduction under the OBBBA is available whether you take the standard deduction or itemize, it applies in addition to either. It is separate from the additional standard deduction for age ($1,650 per qualifying spouse for joint filers in 2026). Both the deduction itself and the income phase-out apply regardless of your filing method.
Rules of thumb only get you so far. The interaction between the senior deduction, IRMAA brackets, Social Security inclusion rates, and your specific income stack makes the right Roth conversion amount genuinely individual, and the numbers have changed enough in 2026 that strategies built even a year ago may need updating.
If you’d like to run the projection for your situation, including a look at your MAGI at different conversion levels and a two-year IRMAA forecast, the team at Madison Partners is glad to work through it with you.
This content is for educational purposes only and should not be considered financial, tax, legal, or investment advice. Individual circumstances vary, and readers should consult with a qualified financial advisor, tax professional, or attorney before making decisions based on this information. Madison Partners does not guarantee the accuracy of third-party data cited herein.
