Fill the bracket without tripping IRMAA or the ACA cliff
Data verified: Aug 2026 · Source: IRS Rev. Proc. 2025-32
A Roth conversion calculator that fills your bracket without spilling into the next, and flags the IRMAA and ACA cliffs a conversion can trip.
Your details
A conversion today sets your Medicare premiums two years from now.
Conversion room in this bracket
—
Current taxable income
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Top of the target bracket
—
Tax on the conversion
—
Effective rate on the converted amount
—
Marginal rate after conversion
—
Room available
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⚠IRMAA: this conversion pushes your MAGI to —, which sets your Medicare premiums two years from now at —. That is — a year more than you pay at your current income.
⚠NIIT: the conversion itself is not net investment income, but it lifts MAGI above the — threshold, exposing — of investment income to the 3.8% surtax — an extra —.
⚠Your income already sits above the top of that bracket. Choose a higher target bracket, or wait for a lower-income year.
✓You can convert — at an effective rate of — without leaving this bracket.
Marginal rate as the conversion grows
Conversion
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How this is calculated
A Roth conversion moves money from a traditional IRA or 401(k) into a Roth account. The entire converted amount counts as ordinary income in the year of the conversion, so the art is converting exactly enough to use up the cheap space in your current bracket without pushing into the next one.
Bracket space is not the only constraint. A conversion raises the MAGI that determines your Medicare premiums two years later, can push a household over the ACA subsidy cliff, can drag more of your Social Security into taxation, and can expose investment income to the 3.8% net investment income tax. This calculator shows the bracket room and flags each of those interactions.
Formula
conversionRoom = top of target bracket − current taxable income
Simple on its own. The complexity is in what else moves when income rises: IRMAA on a two-year lookback, the ACA 400% FPL cliff, the provisional income test for Social Security, and the NIIT threshold.
Worked example
Married filing jointly in 2026 with taxable income of $150,000, filling to the top of the 22% bracket.
Top of the 22% bracket (MFJ)$211,400
Current taxable income$150,000
Tax on the converted amount at 22%$13,508
Conversion room$61,400
The four interactions to check
Bracket room tells you the direct cost. These four tell you the indirect one.
IRMAA operates on a two-year lookback, so a conversion this year sets your Medicare premiums two years out — and it is a cliff, not a slope. Check your tier with the IRMAA Medicare surcharge calculator.
The ACA premium tax credit disappears entirely above 400% of the federal poverty level, so a conversion can cost a household its whole subsidy — see the ACA subsidy cliff calculator before converting.
Social Security taxation rises with provisional income — AGI plus half your benefits plus tax-exempt interest — pulling up to 85% of benefits into tax above $34,000 single or $44,000 joint.
The 3.8% net investment income tax applies to the lesser of your investment income or your MAGI above $200,000 single or $250,000 joint. The conversion is not itself investment income, but it raises the MAGI side of that test.
When conversions make most sense
The classic window is the gap between retiring and starting Social Security or required minimum distributions — income is temporarily low, brackets are cheap, and there is room to fill. A market downturn is another: converting a depressed balance moves more shares for the same tax bill.
Frequently asked questions
Is the whole conversion taxed as ordinary income?
Yes, to the extent it comes from pre-tax money. It receives no capital gains treatment whatsoever, and it stacks on top of your other income for the year rather than being taxed in isolation. If you hold non-deductible IRA basis, the pro-rata rule applies and only part of the conversion is taxable.
Can I undo a conversion I regret?
No. Recharacterization of Roth conversions was eliminated by the Tax Cuts and Jobs Act, so once converted it stays converted even if the market falls immediately afterwards. That irreversibility is exactly why sizing the conversion correctly, and checking the IRMAA and ACA interactions first, matters so much more than it used to.
Should I pay the tax from the converted money?
Generally no. Paying the tax from outside funds moves the full amount into the Roth where it grows tax-free, which is the entire point of the exercise. Withholding from the conversion itself also triggers a 10% early distribution penalty on the withheld portion if you are under 59 and a half.
How long must the money stay in?
Each conversion carries its own five-year clock for penalty-free withdrawal of the converted principal if you are under 59 and a half. That is a separate clock from the five-year rule governing tax-free withdrawal of earnings, so multiple conversions in different years each start their own count.
Why does IRMAA matter if I am not on Medicare yet?
Because of the two-year lookback. If you will be enrolled in Medicare two years from now, this year's conversion is the income that determines those premiums. People converting at 63 are frequently surprised to find their first Medicare year carries a surcharge driven by a conversion made before they enrolled.
Does a conversion affect my ACA subsidy?
Yes, directly and severely. Conversion income counts in full toward ACA MAGI, and crossing 400% of the federal poverty level eliminates the premium tax credit entirely rather than tapering it. For a household on marketplace coverage, a conversion can easily cost more in lost subsidy than it saves in future tax.
IRS Rev. Proc. 2025-32 · SSA Contribution & Benefit Base · CMS Federal Register notice published 2025-11-19 · HHS ASPE 2025 Poverty Guidelines · IRS Rev. Proc. 2025-25
Disclaimer
Estimates for general information only, not tax or investment advice. State income tax, the pro-rata rule for non-deductible IRA basis, and your own Social Security position are not modeled here. Consult a qualified tax professional before converting.