Tax Strategy · 8 min read · 2026-04-30
The 9 signals behind a profitable Roth conversion.
A Roth conversion is one of the few legal arbitrages between today's tax rate and tomorrow's. The discipline is choosing the right year.
A Roth conversion done in the wrong year is a tax acceleration with no payoff.
Roth conversions are a one-way trip — you pay the tax now in exchange for tax-free growth and withdrawals later. Done in a year of high marginal rates, with full IRMAA exposure, or near a market peak, the conversion costs more than it ever recovers. Done in a low-bracket year, into a drawdown, ahead of the TCJA sunset, the conversion is one of the highest-IRR tax decisions available.
The nine indicators
The nine signals that say convert this year.
When most align, the after-tax math favors the conversion. When few align, the deferral is winning.
Current marginal rate < expected retirement rate
Threshold: gap > 5 pp
The fundamental Roth conversion logic. Pay tax at today's lower rate; avoid tomorrow's higher rate. Above 5 percentage points of expected gap, the conversion is structurally favored.
Bracket headroom of $50,000+ before the next bracket break
Threshold: > $50K
Conversion fills the current bracket. With less than $50K headroom, the conversion straddles brackets and the marginal cost rises sharply.
Market drawdown of 15%+ from 12-month high
Threshold: > 15% drawdown
Converting depressed assets transfers more shares per tax dollar paid. Recovery happens inside the Roth, tax-free.
Three or more years before Medicare/IRMAA enrollment
Window: pre-65
IRMAA surcharges look back two years. Conversions in years 63, 64, and 65 cause IRMAA hits at 65, 66, and 67. Conversions before age 63 avoid this entirely.
TCJA sunset year (2025) approaching with no extension
Threshold: < 2 years to sunset
The TCJA's lower brackets sunset at the end of 2025. Conversions before the sunset capture the lower rates; conversions after pay the post-sunset rates.
Estate tax exposure on tax-deferred accounts
Threshold: estate > $13.6M (2026)
Tax-deferred accounts inherit at the beneficiary's tax rate, not stepped-up basis. Conversion shifts the asset out of the most punishing inheritance posture.
Beneficiaries in higher tax brackets than the holder
Pattern: kids earn more than parents
Inherited tax-deferred IRAs require liquidation within 10 years at the beneficiary's rate. If beneficiaries are in higher brackets, conversion saves on the inheritance side.
Required Minimum Distributions are coming
Window: 5–10 years to age 73
RMDs force taxable distributions starting at age 73. Pre-RMD conversions reduce the future RMD base and lower the bracket pressure.
Sufficient outside cash to pay the conversion tax
Source: not from the IRA itself
Paying the tax from the IRA reduces the wealth transferred to the Roth. Paying from outside cash lets the entire converted amount grow tax-free, which is the primary source of compounding alpha.
What a Roth conversion does, mechanically
A Roth conversion moves dollars from a traditional IRA (or 401(k) rollover) to a Roth IRA. The dollars are taxed as ordinary income in the year of the conversion. Once inside the Roth, they grow tax-free and are withdrawn tax-free in retirement. There is no required minimum distribution from a Roth IRA during the holder's lifetime.
The conversion is a tax-rate arbitrage: pay today's marginal rate to avoid tomorrow's. Whether it pays off depends entirely on the rate differential, the time horizon, and whether the tax can be paid from outside cash. The math is sensitive to all three; small changes produce large differences in lifetime after-tax wealth.
Why most retail Roth conversions are mistimed
Brokerages and advisors often present the Roth conversion as a binary 'good idea' or 'bad idea.' It is neither. The conversion is a year-by-year optimization, where the right amount in the right year captures the rate arbitrage and any other year captures less or none. Most retail conversions happen reactively — after a market run, in years of high income, near or after Medicare enrollment — exactly when the math is least favorable.
The single most common mistake is converting in years of high earned income. The conversion stacks on top of W-2 income and pushes the converted amount through the higher brackets. The result is paying the highest marginal rate of the holder's life on the converted dollars, which is the opposite of the strategy.
Bracket-management and the gap year strategy
The richest Roth conversion years are typically the low-income years between final paycheck and Social Security or RMD onset. A retiree who stops working at 62 has potentially eight to eleven years of low taxable income before age 73 RMDs begin. Each of those years is a conversion opportunity, capped at the top of the holder's preferred bracket — typically the 12% or 22% bracket.
The discipline is to project the multi-year tax picture and convert annually up to the bracket cap. Filling the 12% bracket every year for eight years often shifts $400,000–$700,000 from traditional to Roth at a blended rate of 9–11 percent — well below the rates the same dollars would have faced inside RMDs.
The IRMAA cliff
Medicare's Income-Related Monthly Adjustment Amount surcharges look back two years. A conversion in 2026 affects Medicare premiums in 2028. The surcharges step up at five income thresholds, with the largest cliff producing approximately $5,000 of additional Medicare premium per couple per year.
The IRMAA structure penalizes conversions in years 63, 64, and 65 (which produce IRMAA hits in years 65, 66, and 67) and rewards conversions earlier. The screen is simple: if Medicare enrollment is more than three years away, the IRMAA constraint is non-binding. Inside three years, every conversion dollar must be evaluated against the IRMAA bracket structure.
Drawdowns are conversion windows
Converting depressed assets is mathematically superior to converting peaks. The same tax bill transfers more shares; recovery happens inside the Roth, tax-free, on the larger share count. A 25% drawdown converts to a 33% larger Roth balance at the same tax cost.
The discipline is preparation. The conversion needs to happen quickly when the drawdown materializes — most major drawdowns last only 6 to 18 months, and the conversion math improves further as the drawdown deepens. Pre-positioning the cash to pay the tax, completing the IRA-to-Roth transfer paperwork, and identifying the conversion-eligible assets all need to happen before the drawdown, not during it.
Pay the tax from outside cash
Paying the conversion tax from the converted IRA itself defeats most of the point. If a $100,000 conversion produces a $24,000 tax, paying that tax from the IRA reduces the Roth balance to $76,000 — and the holder forfeits the tax-free growth on the $24,000 forever. Paying the same tax from outside taxable cash leaves the full $100,000 inside the Roth, growing tax-free.
The lifetime IRR difference between in-IRA and outside-cash payment is meaningful — typically 80–150 basis points of additional terminal wealth per conversion year, compounded over a 25-year horizon. The discipline is to size conversions only up to the available outside cash.
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Common questions
Questions.
Can I undo a Roth conversion?
No. The Tax Cuts and Jobs Act eliminated the recharacterization option in 2018. Conversions are permanent. The pre-conversion analysis must be right because there is no remediation.
What's the deadline to convert for the current tax year?
December 31. Unlike IRA contributions (which extend to April 15), conversions must be completed in the calendar year to count for that year.
Does a backdoor Roth count as a conversion?
Yes, technically. Backdoor Roths involve a non-deductible traditional IRA contribution followed by an immediate conversion. The pro-rata rule applies if there are pre-tax IRA balances; this is the most common backdoor pitfall.
Should I convert all at once or over multiple years?
Almost always over multiple years, sized to fill the preferred bracket each year without overflow. A single large conversion typically straddles brackets and pays more tax than necessary.
What if I'm already retired and on Social Security?
Social Security taxation creates a non-linear marginal rate environment between roughly $25,000 and $44,000 of provisional income. Conversions in that band can produce effective marginal rates of 22–40%. Modeling is necessary; the rule of thumb is to convert below the band or above it, not through it.
Does the 5-year rule apply?
Yes, but on a per-conversion basis. Each conversion has its own 5-year clock for tax-free withdrawal of the converted principal before age 59½. Withdrawals after 59½ from any Roth funded for at least 5 years are unrestricted.
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