Everywhere you turn right now, financial pundits are recommending Roth conversions.
“Taxes are going up.” “Convert while rates are low.” “Fill the bracket.”
And while Roth conversions can absolutely be powerful planning tools, there’s a major problem with the way they’re often discussed:
Most people are looking only at the tax bracket — not the
true cost of the conversion.
At Beyond Wealth Partners, we spend a significant amount of time modeling Roth conversion strategies for P&G retirees and executives. What we’ve found is that the
effective tax rate of a conversion can be dramatically higher than the marginal bracket printed on the tax tables.
In some cases, a “12% conversion” can actually behave more like a 22% conversion once the ripple effects across the tax return are fully accounted for.
That’s why tax-aware Roth conversion planning requires more than intuition. It requires high-level tax software, scenario analysis, and a deep understanding of how increases in Adjusted Gross Income (AGI) impact the rest of the return.
The Hidden Cost of Higher AGI
When you perform a Roth conversion, you increase taxable income and AGI. That sounds simple enough.
But AGI acts like a master switch throughout the tax code.
A higher AGI can trigger:
- Increased taxation of Social Security
- Loss of senior deductions
- Higher Medicare IRMAA premiums
- Loss of ACA subsidies
- Phaseouts of credits and deductions
- Higher capital gains exposure
- Additional state tax consequences
In other words, the conversion itself may not be the real tax cost.
The
side effects are often the bigger issue.
A Real-World Example
Recently, we analyzed two Roth conversion strategies for a retired couple.
The goal was straightforward: Determine whether it made sense to convert enough assets to fill the 12% bracket — or aggressively convert into the 22% bracket.
At first glance, many advisors would instinctively recommend “filling the bracket.”
But the analysis told a much more nuanced story.
Scenario #1 — Controlled Conversion
We modeled a Roth conversion of approximately
$40,000.
This strategy intentionally kept income near the top of the 12% bracket while preserving several important tax benefits.
Why we preferred this route:
- Nearly the entire Enhanced Senior Deduction was preserved
- The couple avoided meaningful IRMAA exposure
- Federal tax burden remained manageable
- Cash reserves stayed largely intact
- Future flexibility remained available
Most importantly, the analysis showed something many investors miss:
Although the income sat inside the
12% marginal bracket, the
effective tax rate on the next dollars converted was actually over
22% due largely to increased taxation of Social Security income.
That distinction matters enormously.
Scenario #2 — “Fill the 22% Bracket”
We then modeled a far larger Roth conversion of approximately
$137,000.
On paper, this sounds appealing: “Let’s convert more while tax rates are still historically low.”
But once we modeled the
full tax impact, the picture changed dramatically.
The larger conversion caused:
- Elimination of the Enhanced Senior Deduction
- Much higher federal and Ohio tax liability
- Reduced flexibility for realizing future capital gains
- Significant pressure on cash reserves
- Increased taxation of Social Security benefits
And again, despite the conversion “living” in the 22% bracket, the true effective rate on incremental income climbed materially higher when all interactions were included.
This is exactly why bracket-based planning alone can be misleading.
The Difference Between Marginal and Effective Conversion Rates
This is one of the most misunderstood concepts in retirement tax planning.
Your marginal bracket is simply the rate assigned to the
next dollar of ordinary income.
But Roth conversions often create hidden chain reactions:
- More Social Security becomes taxable
- Deductions phase out
- Medicare costs rise later
- Other income becomes exposed to tax
That means the
actual economic cost of the conversion may be far higher than the bracket itself suggests.
In our planning process, we focus heavily on:
- Effective conversion rates
- Multi-year tax projections
- Medicare thresholds
- Future RMD management
- Legacy planning
- Cash flow sustainability
Because the objective is not simply to “convert more.”
The objective is to improve
lifetime after-tax wealth.
Roth Conversions Are Still Powerful
To be clear — this is not an anti–Roth conversion argument.
In fact, we believe Roth conversions can be extraordinarily valuable when used correctly.
But the best Roth conversion strategies are usually:
- Intentional
- Multi-year
- Tax-aware
- Coordinated with Social Security and Medicare
- Customized to the household
The days of simplistic “fill the bracket” advice are over.
Sophisticated planning requires understanding how every additional dollar of income interacts with the broader tax system.
And sometimes, the smartest conversion is the smaller one.
