Roth Conversion Tax Calculator 2026

Enter your filing status, other income, and the amount you want to convert. The calculator shows the exact federal tax on the conversion, which brackets it hits, how much room remains in your current bracket, and whether the conversion triggers an IRMAA Medicare surcharge.

How to read these results

Effective rate vs. marginal rate

The effective rate on your conversion is the blended rate across all brackets the conversion touches. If you convert $40,000 that falls entirely in the 12% bracket, the effective rate is exactly 12%. If the conversion spills into a higher bracket, the effective rate is a weighted average — lower than the top bracket rate but higher than the bottom one. The effective rate is what matters when comparing "pay tax now vs. defer."

Conversion room at your current top rate

This is how much more you could convert this year before the next dollar crosses into a higher bracket. Bracket-filling is a common multi-year Roth conversion strategy: convert up to the ceiling of your current bracket each year, stay at the lower rate, and repeat. A financial advisor can model this sequence across your pre-RMD retirement window.

Standard deduction

The calculator applies the 2026 standard deduction automatically — $32,200 for married filing jointly, $16,100 for single filers (IRS Rev. Proc. 2025-32). If you itemize deductions, enter gross income and adjust: treat itemized deductions in excess of the standard deduction as a reduction to your "other income" input.

2026 tax brackets (for reference)

These are taxable income thresholds — after subtracting the standard or itemized deduction — at which each federal rate applies.

Source: IRS Rev. Proc. 2025-32. Values verified May 2026.

The IRMAA cliff: the hidden cost for Medicare beneficiaries

If you or your spouse are enrolled in Medicare, a large Roth conversion can trigger the Income-Related Monthly Adjustment Amount (IRMAA) — a Medicare surcharge that increases Part B and Part D premiums. Medicare uses income from two years prior: your 2026 taxable events determine your 2028 Medicare premiums.

The 2026 IRMAA Tier 1 threshold is $109,000 MAGI for single filers and $218,000 for married filing jointly.² The Tier 1 surcharge adds $81.20/month per Medicare beneficiary above the $202.90 base Part B premium — $974/year per person. For a couple where both spouses are on Medicare, crossing the threshold costs $1,948/year on top of the conversion tax.

IRMAA is a step function: crossing the threshold by $1 triggers the full surcharge. Stopping your annual conversion $1 below the threshold is usually worth it — and the calculator flags when you're in that position.

The 5-year rule on converted funds

Each Roth conversion starts its own 5-year holding period. If you withdraw converted principal within 5 years of the conversion date and you are under age 59½, you owe a 10% early-withdrawal penalty on that principal — on top of the income tax you already paid at conversion. Roth IRA earnings have a separate 5-year clock that starts when you first open any Roth IRA.

After age 59½, neither clock applies to the 10% penalty. This means converting at 54 and planning to access the money at 59½ is safe — the 5-year principal clock expires before 59½, and at 59½ you're penalty-free regardless.

When conversion math favors Roth

• Your current rate is lower than your expected future rate. You retire before Social Security starts; income drops; you convert at 12% before RMDs push you to 22%.
• You want to reduce future RMDs. Converting now shrinks the pre-tax IRA balance that will generate forced taxable distributions at 73 or 75. Smaller RMDs mean more flexibility and potentially lower Medicare costs.
• You're passing the IRA to heirs. Non-spouse beneficiaries must deplete inherited IRAs within 10 years under the SECURE Act — possibly at high marginal rates during their own peak-earning years. A Roth IRA passes tax-free with no RMDs during the original owner's lifetime.
• You can pay the tax from outside the IRA. Using savings to pay the conversion tax, rather than withholding from the converted amount, maximizes how much ends up in Roth. Withholding from the IRA is effectively converting less money — and may trigger an early-withdrawal penalty on the withheld portion if you're under 59½.

When to pause

• Crossing the IRMAA threshold costs more in Medicare surcharges than the long-run conversion benefit.
• Your current bracket is the same or higher than you expect in retirement — deferral wins.
• You have non-deductible IRA contributions tracked on Form 8606 and the pro-rata rule applies. Check the pro-rata rule guide before converting.
• You'd need to withhold the conversion tax from the IRA itself — this reduces the Roth end-balance and may cost more than the benefit provides.

1. IRS Rev. Proc. 2025-32 — 2026 inflation-adjusted tax parameters: bracket thresholds for all seven rates (10%–37%), standard deductions ($32,200 MFJ / $16,100 single). Verified May 2026.
2. CMS — 2026 Medicare Parts A & B Premiums and Deductibles — Part B base premium $202.90/month; IRMAA Tier 1 surcharge $81.20/month per beneficiary. Threshold: $109,000 single / $218,000 MFJ (2024 MAGI). Published November 2025.
3. IRS Publication 590-B — Distributions from Individual Retirement Arrangements — 5-year rule for Roth conversions, ordering rules for Roth IRA withdrawals, early-withdrawal penalty on converted principal.
4. IRS IR-2025 — 2026 Tax Inflation Adjustments — Confirms Roth conversion eligibility is not income-limited. 2026 Roth IRA direct contribution phaseout: $150,000–$165,000 single, $236,000–$246,000 MFJ (conversions have no limit).

Tax values verified May 2026 against IRS Rev. Proc. 2025-32 and CMS.gov. Calculator outputs are estimates and do not account for state income tax, Social Security taxation, or the net investment income tax (NIIT).

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