A Roth conversion moves money from tax-deferred to tax-free by paying the tax today. Whether that trade pays off depends on one comparison: the blended rate you pay now against the rate you would pay at withdrawal. This calculator uses the 2026 brackets to price the conversion, finds your exact break-even future rate, and flags the Medicare surcharge a big conversion can trigger.
A Roth conversion does two things at once. It triggers tax on the converted amount today, at whatever marginal rates your other income leaves open, and it removes the future tax bill that amount would otherwise owe at withdrawal. Everything else people say about conversions, from tax-free growth to avoiding required minimum distributions, is secondary to that trade. The math is a comparison of two tax rates applied to the same dollars, and the honest way to run it is to compute both sides precisely.
The rate you pay today is rarely the bracket you think you are in. Converting $50,000 while earning $60,000 of other income pushes you through the top of the 22 percent bracket into the 24 percent one, so part of the conversion is taxed at 22 percent and part at 24 percent. The average of those pieces, the blended marginal rate, is your real conversion price. The rate you avoid at withdrawal is equally uncertain, which is why this calculator reports a break-even rate rather than a verdict.
Variables in plain terms. Other income is your taxable income for the conversion year from all other sources, which sets where the conversion lands in the 2026 brackets. The conversion amount is what you move from a traditional IRA or 401(k) to a Roth. The growth rate r and holding period y apply to both sides of the comparison, so they shape the dollar stakes but never the break-even decision. The future rate f is your expected marginal federal rate when the money comes out. The net advantage formula has a clean interpretation: converting wins by exactly the difference between the future rate and today's blended rate, compounded. If your future rate would equal the blended rate you pay today, the conversion is a wash, worth nothing either way.
A single filer with $60,000 of other taxable income converts $50,000. The 2026 tax on $60,000 alone is $7,912. Adding the conversion pushes taxable income to $110,000, where the tax is $18,998. The conversion costs the difference: $11,086. That bill splits across two brackets, $45,700 taxed at 22 percent and $4,300 taxed at 24 percent, for a blended rate of 22.17 percent.
| Bracket | Converted amount taxed there | Tax |
|---|---|---|
| 22% | $45,700.00 | $10,054.00 |
| 24% | $4,300.00 | $1,032.00 |
| Blended | $50,000.00 | $11,086.00 (22.17%) |
Now the ten years. Invested at 6 percent, the $50,000 compounds by a factor of 1.7908. Converted to a Roth and left alone, it reaches $89,542.38, owed to no one. Left in the traditional account and withdrawn at a 24 percent marginal rate, the same balance nets $68,052.21. But fairness requires counting the tax bill itself: the $11,086 paid today would otherwise have compounded to $19,853.34. The conversion wins by $1,636.83. The break-even tells you how fragile that margin is: any future marginal rate above 22.17 percent favors converting, any rate below favors waiting. At a 22 percent future rate the conversion actually loses $154.02, because that final $4,300 spillover into the 24 percent bracket raised today's price above tomorrow's.
Contrast that with a filer lower down the brackets. The same $50,000 conversion for a single filer with $30,000 of other income costs $8,960, a blended 17.92 percent, because $20,400 of it fills the 12 percent bracket first. At the default future rate of 24 percent, converting still wins by $5,444.18. Trim the conversion to $25,000 and the bill drops to $3,460, a blended 13.84 percent. Filling the low brackets is the entire strategic core of conversion planning, and it is why conversions cluster in early retirement, between the last paycheck and Social Security claiming.
At the defaults, the 22 percent bracket tops out at $105,700 of taxable income for a single filer. With $60,000 of other income, exactly $45,700 of conversion room remains at 22 percent. Converting that amount costs $10,054, precisely 22 percent, and the break-even future rate is exactly 22 percent. Going $4,300 past it is what pushed the blended rate to 22.17 percent and turned a wash into a small loss at a 22 percent future rate. The practical rule: decide the rate you are willing to pay, then convert up to the bracket boundary, not past it. Larger conversions are not wrong, but each dollar past the boundary needs the future rate to justify it.
Married filers get roughly double the room. A joint filer with $120,000 of other income can convert $60,000 entirely inside the 22 percent bracket, which ends at $211,400 for 2026, for a tax of $13,200 and a break-even of exactly 22 percent. Lower incomes compress the math further. A filer with $30,000 of other income converting $25,000 pays $3,460, blended 13.84 percent, and that conversion wins against any future rate above 13.84 percent.
The comparison above assumes the $11,086 tax bill is paid from savings outside the retirement accounts. Paying it from the IRA itself, by converting $50,000 and withholding the tax, leaves only $38,914 working for you. After ten years at 6 percent that grows to $69,689.05, which is $19,853.34 short of the outside-funded Roth, exactly the compounded value of the tax dollars you surrendered. There is also a mechanical problem: under IRS rules, taxes withheld from a conversion are treated as a distribution, and before age 59 and a half that distribution carries the 10 percent early-withdrawal penalty. Convert the full amount, wire the tax from your checking account, and both problems disappear.
| Funding route | Roth value in 10 years | Difference |
|---|---|---|
| Tax paid from outside savings | $89,542.38 | — |
| Tax taken from the IRA | $69,689.05 | −$19,853.34 |
Hold the defaults constant and move only the future marginal rate. At 12 percent, staying traditional wins by $9,108.26. At 22 percent, converting loses $154.02. At 24 percent, converting wins by $1,636.83. At 32 percent, converting wins by $8,800.23. The current-law brackets, made permanent by the 2025 tax legislation according to Tax Foundation analysis, will not last forever in this exact shape, and your own withdrawal years may stack income differently than you expect. The robust conversions are the ones with a low blended rate, where the future rate has to fall dramatically before the math flips. Conversions priced near today's top rates deserve skepticism no matter how confident the projection.
Two frictions push the other direction. A conversion adds its full amount to MAGI, and Medicare premiums are set from the return filed two years earlier, so the default example's $110,000 MAGI crosses the first IRMAA threshold and roughly doubles the standard Part B premium from $202.90 to $405.80 a month, per CMS. The Medicare IRMAA calculator maps those cliffs in detail. And conversions made under 59 and a half carry the 10 percent penalty on any tax withheld from the account, covered in the FAQ below. Neither changes the break-even rate, but both change whether a specific year is the right year.
For most savers the conversion decision sits inside a larger question about which account to fund in the first place, which the Roth vs Traditional IRA calculator handles from the contribution side. And once tax-free money exists, the spending order in retirement matters just as much, which is where the retirement withdrawal calculator comes in.
Nobody knows, which is exactly why the break-even rate is the calculator's most useful output. Current-law rates were made permanent by the 2025 tax legislation, but future Congresses can change them, and your own retirement rate depends on your withdrawal mix. A defensible approach is to run the calculator at several rates and act only on the conclusions that survive. If converting still wins at a future rate a few points above today's brackets, the decision is robust. If it only wins when rates fall, it is a bet, not a plan.
A conversion stacks on top of your other taxable income, so the incremental tax is the difference between the tax on your income alone and the tax on your income plus the conversion. That is why the calculator asks for other taxable income rather than your marginal bracket. The same $50,000 conversion costs $11,086 for a single filer with $60,000 of other income but $8,960 for one with $30,000, because the second person fills the 12 percent bracket first. Retirees with low-income years can convert at a blended rate in the teens, which is the whole appeal of converting between retirement and Social Security claiming.
From outside savings, if you have it. Withholding from a conversion counts as a distribution, which triggers the 10 percent early-withdrawal penalty if you are under 59 and a half, so paying from the account means wiring the tax separately anyway or eating the penalty. The compounding cost is larger than people expect: at the calculator defaults, funding the $11,086 tax bill from the IRA leaves a Roth worth $69,689 in ten years instead of $89,542, because the $11,086 loses its own ten years of growth. One caveat: if your IRA contains after-tax contributions, the pro-rata rule applies and part of any conversion is tax-free.
It can, and the effect lands two years later. The income-related monthly adjustment amount, IRMAA, is set from the tax return filed two years before the coverage year, and a conversion adds its full amount to MAGI. At the calculator defaults, a single filer with $60,000 of other income who converts $50,000 lands at $110,000 of MAGI, which crosses the first 2026 IRMAA threshold of $109,000 and roughly doubles the standard Part B premium from $202.90 to $405.80 per month, per CMS. Sometimes the IRMAA hit costs more than the conversion saves, which is a reason to split a large conversion across years.
Each conversion starts its own five-year clock. Withdraw the converted principal before the clock ends and before you reach 59 and a half, and the 10 percent early-distribution penalty applies to it, though the money is never taxed again. Earnings follow the standard Roth rules: tax- and penalty-free only after the account has been open five years and you are at least 59 and a half. This is why a conversion is a retirement tax move, not an early-access loophole.
No. Recharacterization, the old do-over that let investors undo a conversion after the market fell, was eliminated for conversions made in 2018 and later. The modern substitute is discipline about size: convert in December using nearly-final income numbers, and split a large planned conversion across multiple years so a single overshoot cannot trigger an IRMAA surcharge or a bracket jump you did not intend. Once the conversion is done, the tax is owed for that year and the clock cannot be unwound.