Roth Conversion Calculator

What does converting really cost this year? Bracket-fill headroom, the Social Security tax torpedo, IRMAA cliffs, the senior-deduction phase-out, capital-gains stacking — and how your state treats conversions (a few don't tax them at all). 2026 rules, all in your browser; your numbers never leave this computer.
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Your data:
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You required

Your 2026 income — before the conversion required

⚙️ More detail — tax-exempt interest
Use your best estimate of the full year, and enter income before any deduction (AGI-style — what lands on the income lines of your 1040), not the "taxable income" line: the calculator subtracts the 2026 standard deduction ($16,100 single / $32,200 joint, plus the 65+ extras) for you. If you itemize much more than that, your bill will be a bit lower than shown.

The conversion the decision

"Filling a bracket" is the classic strategy: convert enough to use up the room left in a low bracket, and stop before the next rate kicks in. The chart on the right shows where every cliff and rate jump actually lands — some of them (Social Security taxation, IRMAA) hit before the bracket line does.

The bill for this conversion

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Federal tax on conversion
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State tax on conversion
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Medicare IRMAA (2028)
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Average rate on conversion
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Rate on the LAST dollar
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Room left in bracket
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The real cost of each converted dollar

This curve is the whole point of the tool: the combined federal + state marginal rate on each additional dollar you convert. The spikes aren't errors — they're the Social Security "tax torpedo" (each conversion dollar drags up to $0.85 of benefits into taxable income), the 65+ senior-deduction phase-out, capital-gains stacking (conversion dollars push your 0%-taxed gains into 15%), and NIIT. Gold verticals are IRMAA cliffs — $1 over one of those costs a full year of higher Medicare premiums in 2028.

Where the money goes, dollar by dollar

Good-to-know moves

  • There is no undo. Recharacterization is gone — a conversion is permanent. Converting in November–December, when you can see the whole year's income, beats guessing in January.
  • Pay the tax from outside money, not from the conversion itself. Withholding from the conversion shrinks what reaches the Roth — and if you're under 59½, the withheld part is itself a taxed and penalized distribution.
  • RMD first: if you're 73+, the year's required minimum distribution must come out before any conversion — RMDs themselves can never be converted.
  • The IRS wants its money during the year. A big conversion can trigger an underpayment penalty even if you pay in April. Easy fixes: quarterly estimated payments, or the safe harbor (prepay 100% of last year's tax — 110% if AGI was over $150k), or year-end withholding from an IRA/pension, which counts as if paid evenly all year.
  • Each conversion starts its own 5-year clock if you're under 59½ — pulling converted dollars back out within 5 years costs a 10% penalty. After 59½ that clock stops mattering.
  • IRMAA has a two-year lag and no mercy: 2026 income sets your 2028 Medicare premiums, the tiers are cliffs (not phase-ins), and the surcharge applies per spouse on Medicare. One dollar over a line = twelve months of the full surcharge.
  • Check the state column before you move — or convert before you move. Illinois, Pennsylvania, Mississippi, and Iowa (55+) tax conversions at zero; California and Oregon take ~10%+. Timing a conversion around a relocation can be worth five figures.

📍 State-by-state Roth conversion guide reference

Nobody should move for a conversion — but timing one around a move can be worth five figures, and knowing your state's rules is free. 9 states have no income tax, 4 more (Illinois, Pennsylvania, Mississippi, and Iowa at 55+) don't tax conversions at all, about a dozen offer age-gated exclusions that can absorb part of one — and a few high-rate states with no relief are where the big mistakes happen. Pick your state above to highlight your row.
2026 rules gathered from state revenue sources in July 2026. Rows marked ⚠ in their notes have exclusion mechanics that are solid but not explicitly documented for conversion income — verify with your state or a preparer before relying on them. Exclusion caps are usually shared with other pension income.