If you are 65 or older and still doing Roth conversions without accounting for the new senior deduction, you may be leaving thousands of dollars on the table, or worse, paying far more tax than you realize.
The One Big Beautiful Bill Act (OBBBA), signed into law in 2025, introduced a temporary $6,000 deduction for taxpayers age 65 and older. On the surface, this sounds like a simple tax break. In reality, it creates a hidden effective tax rate increase in a specific income range that can turn an otherwise well-sized Roth conversion into an expensive mistake.
Here is what you need to know.
First, the Good News: The New Senior Deduction
The OBBBA added a brand-new deduction, separate from anything that existed before, for taxpayers aged 65 and older. The amThe OBBBA added a brand-new deduction, separate from anything that existed before, for taxpayers aged 65 and older. The amounts are:
- $6,000 for single filers
- $12,000 for married couples filing jointly when both spouses are 65 or older
This deduction stacks on top of your standard deduction and the existing age-related add-on deduction. It is also available whether you take the standard deduction or itemize. It applies to tax years 2025 through 2028, after which it is scheduled to expire unless Congress acts.
For a married couple where both spouses are 65 or older, that is a combined potential 2026 deduction of:
- $32,200 base standard deduction
- $3,300 age add-on ($1,650 per spouse)
- $12,000 senior bonus deduction
That is roughly $47,500 of income potentially sheltered before a single dollar of federal income tax is owed. For many retirees in the early RMD-free years, this is meaningful.
Now, the Complication: The Phase-Out
The senior deduction is not available to everyone at every income level. It phases out based on your Modified Adjusted Gross Income (MAGI), and the phase-out creates a significant planning wrinkle.
| Filing Status | Phase-Out Begins | Fully Eliminated At |
|---|---|---|
| Single | $75,000 MAGI | $175,000 MAGI |
| Married Filing Jointly | $150,000 MAGI | $250,000 MAGI |
The deduction reduces at a rate of 6% for every dollar of MAGI above the threshold. For a married couple, that means every additional $1 of income above $150,000 reduces the deduction by 6 cents. Over the full $100,000 phase-out range, the entire $12,000 deduction disappears.
What does that mean in real terms? If you are in the 22% federal bracket and your MAGI is in the phase-out zone, losing 6 cents of deduction per dollar of income effectively adds 1.32 percentage points to your marginal rate. For someone in the 22% bracket, losing 6 cents of deduction per dollar of income adds approximately 1.32 percentage points to the marginal rate, pushing it to roughly 23.3% inside the phase-out window. If other phase-outs are stacking at the same time, such as increased Social Security taxation or IRMAA surcharges, the combined effective rate can climb meaningfully higher still.
Why This Matters for Roth Conversions
A Roth conversion adds directly to your MAGI for the year it occurs. If you are a 65-or-older couple sitting at $140,000 of income from Social Security, pensions, and investments, a $30,000 Roth conversion pushes your MAGI to $170,000. You have just moved $20,000 into the phase-out zone, eroding $1,200 of the senior deduction in addition to paying ordinary income tax on the conversion itself.
This does not mean Roth conversions are a bad idea. It means the sizing of each conversion requires more precision than it did before.
There are three specific scenarios where this phase-out matters most:
1. Couples just below the $150,000 threshold. If your baseline MAGI sits at $130,000 and you convert $40,000, you push $20,000 into the phase-out zone. A portion of your conversion is taxed at an effective rate that is meaningfully higher than your nominal bracket suggests.
2. Retirees with large RMDs. Required minimum distributions from traditional IRAs and 401(k)s count toward MAGI. So does the taxable portion of Social Security. If your RMDs alone push you to $160,000, you may have very little conversion room left before you start eroding the senior deduction.
3. Single filers with a lower threshold. Singles face a phase-out that begins at $75,000 and ends at $175,000. That is a tighter range, and it is reached more quickly, especially for those with pensions, Social Security, and any investment income layered together.
The Case for Conversions Still Holds, With Precision
None of this means you should stop converting. The strategic rationale for Roth conversions remains strong in 2026. With the TCJA rate structure now permanent under the OBBBA, you are no longer converting to beat a sunset. Instead, the case rests on three pillars:
Your own rate will likely rise at age 73 or 75. When RMDs kick in, they can push you into a higher bracket. Converting now at a lower rate, before that mandatory income begins, remains a powerful strategy for reducing lifetime taxes.
The senior deduction creates a temporary planning window. Because it expires after 2028, you have a four-year period where careful conversion sizing can work with the deduction rather than against it. A couple with $120,000 of baseline income might be able to convert $25,000 per year while staying fully within the deduction range.
Roth assets improve estate planning. Non-spouse heirs who inherit traditional IRA assets are subject to the 10-year drawdown rule and will pay ordinary income tax on every distribution. Roth assets inherited under the same rules produce tax-free income for heirs. Converting now shifts the tax burden from a period your heirs would face, often at their peak earning years, to a period when your own rate may be more favorable.
What to Watch Alongside the Senior Deduction
IRMAA. Medicare Part B and Part D surcharges are based on your MAGI from two years prior. The IRMAA thresholds and the senior deduction phase-out thresholds do not perfectly align, which creates situations where a conversion can trigger both a higher effective tax rate this year and a Medicare surcharge two years from now. Both need to be modeled together.
Social Security taxation. Social Security benefits are included in MAGI for purposes of the senior deduction phase-out. If you have substantial Social Security income, your baseline MAGI may be higher than you expect before you convert a single dollar.
Practical Illustration
Consider Mike and Linda, both age 67, married filing jointly. Their income sources are:
- Social Security: $42,000 (taxable portion approximately $35,700)
- Pension: $24,000
- Investment income: $18,000
- Total baseline MAGI: approximately $77,700
They are well below the $150,000 threshold. With careful planning, they could convert roughly $70,000 before reaching the phase-out range, paying 12% to 22% federal tax on the conversion depending on how the brackets stack, while preserving the full $12,000 senior deduction. Every dollar converted now is a dollar that will not produce a taxable RMD at 73.
Now consider the same couple with a pension of $70,000 instead of $24,000. Their baseline MAGI rises to roughly $123,700. They can only convert about $26,000 before entering the phase-out zone. Beyond that, each converted dollar begins eroding their deduction, and the effective rate climbs above their nominal bracket. That does not mean no conversion. It means a smaller, more targeted one.
The Bottom Line
The OBBBA senior deduction is genuinely valuable. For eligible retirees with MAGI well below the phase-out threshold, it reduces taxable income by $6,000 to $12,000 per year through 2028 with no strings attached.
But for those in the phase-out range, between $75,000 and $175,000 for singles or $150,000 and $250,000 for couples, Roth conversion sizing requires more precision than a simple bracket fill. The effective marginal rate in that zone is higher than it looks, and ignoring it means paying more tax than necessary.
The question is no longer simply, “Should I convert?” It is: “How much should I convert, and at what income level does the next dollar start costing me more than I think?”
That is exactly the kind of question that retirement income planning should answer before you act, not after.
