Roth Conversion All-In Tax Calculator (2026)

Most retirement calculators show only federal income tax. But a Roth conversion can trigger three more tax layers simultaneously — each interacting with the others. This calculator estimates your complete all-in tax cost: federal bracket cost, Social Security torpedo, IRMAA Medicare surcharge, and state income tax in one place.

Why you need all four layers together: The SS torpedo and IRMAA both depend on your post-conversion MAGI — so running three separate calculators and adding them manually gives the wrong answer. This tool computes them in sequence so the interactions are properly captured.

Filing status

People on Medicare

Annual Social Security benefit ($) Enter the combined annual gross SS benefit for all recipients in this household. Enter 0 if you haven't started collecting.

Other annual income — before any conversion ($) Include: pension, annuity, part-time wages, dividends, interest, RMDs, capital gains. Exclude your SS benefit (entered above) and the Roth conversion amount.

Roth conversion amount this year ($)

State

I am age 65 or older (adds $2,050 to standard deduction for single / $1,650 for MFJ)

Spouse is also age 65 or older (adds another $1,650)

The four layers — why you can't model them separately

Layer 1: Federal income tax (bracket effect)

A Roth conversion is ordinary income — it stacks on top of your other income and gets taxed at your marginal bracket rate. In 2026, the brackets for a married couple are 12% up to $100,800 of taxable income, 22% up to $211,400, and 24% up to $403,550. Conversions that fill the 22% bracket cost 22 cents per dollar. The challenge is that your "other income" — pension, dividends, RMDs, Social Security — may already put you partway into a bracket before the conversion starts.

Layer 2: The Social Security torpedo

When your combined income rises, more of your Social Security benefit becomes taxable — from 0% to up to 85%. This is a hidden multiplier on your marginal rate. In the IRC § 86 phase-in zones, each dollar of conversion income causes an additional 50 cents or 85 cents of SS income to become taxable. For a couple in the 22% bracket, that can push the effective marginal rate to 27–29%. The torpedo only applies while you're still in a phase-in zone. If you're already past the 85% cap, additional conversions have no torpedo effect at all.

Layer 3: IRMAA Medicare surcharge

If your MAGI (which includes taxable SS) crosses the IRMAA thresholds — $109,000 single / $218,000 married for 2026 — Medicare Part B and Part D premiums jump. The surcharge is an annual per-person cliff, not a gradual ramp. Tier 1 costs $1,148/year per enrollee; Tier 2 costs $2,885/year. Two important notes: IRMAA uses your income from two years ago (conversions done now affect 2028 Medicare), and the SS torpedo affects your MAGI — so you can't check IRMAA without first knowing how much SS becomes taxable.

Layer 4: State income tax

Nine states have no income tax. Four more (IL, IA, MS, PA) exempt retirement income distributions. But California, New York, Minnesota, Oregon, and others charge 6–10% on IRA conversions — the same as any ordinary income. State tax applies to the full conversion dollar-for-dollar; unlike federal, there is no standard deduction interaction to model here.

Related tools and guides

Have a specialist build your complete conversion plan

This calculator estimates one year in isolation. A fee-only specialist builds the full 10–15 year model: how your brackets change as RMDs start, which years to convert heavily and which to hold back, how Social Security claiming age changes your annual room, and exactly when the lifetime NPV tips decisively in favor of converting. Free match, no obligation.

Fee-only · No commissions · Free match · No obligation

Limitations of this calculator

Long-term capital gains. If you have LTCG, a Roth conversion can push gains out of the 0% bracket and into the 15% rate. This is not modeled here — use the Capital Gains + Roth Conversion Calculator to see that interaction.
Pro-rata rule. If your IRA has after-tax (non-deductible) basis, a portion of each conversion is tax-free. This lowers your actual federal and state tax cost. Track your basis on Form 8606.
Standard deduction only. The calculator uses the 2026 standard deduction plus the age-65+ additional deduction. If you itemize, your effective taxable income before conversion will be lower — enter your total income minus your actual deduction as "other income" for a more accurate estimate.
OBBBA senior deduction. If you're 65+ with MAGI under $75,000 single / $150,000 MFJ, you may qualify for an additional $6,000 deduction per person under the One Big Beautiful Bill Act. This isn't modeled because it phases out based on post-conversion MAGI — a circular calculation.
IRMAA is a two-year lookback. Shown IRMAA costs apply to the Medicare benefit year two years from now. Actual 2028 thresholds will be published in late 2027 and will likely be 3–6% higher than today's 2026 thresholds used here.
State rates are approximate. State income tax treatment of IRA distributions varies widely. Some states offer partial retirement income exclusions, age-based credits, or graduated rates that change at different income levels. Verify with your state tax authority before planning.
One year in isolation. Optimal Roth conversion planning is a multi-year problem. Converting $100K this year is the right call only if it fits your 10-year bracket and IRMAA trajectory.

Sources

IRS Rev. Proc. 2025-32 — 2026 federal income tax brackets, standard deduction ($32,200 MFJ / $16,100 single), and age-65+ additional deduction ($1,650 MFJ / $2,050 single per person). irs.gov/pub/irs-drop/rp-25-32.pdf
IRC § 86 — Social Security and Tier 1 Railroad Retirement Benefits taxation thresholds. Thresholds ($32,000/$44,000 MFJ; $25,000/$34,000 single) are statutory and have not changed since 1993. law.cornell.edu/uscode/text/26/86
Kiplinger — Medicare Premiums 2026: IRMAA Brackets and Surcharges for Parts B and D. 2026 Tier 1 at $109,000 single / $218,000 MFJ; Part B base $202.90/mo; Tier 1 surcharge $81.20/mo. kiplinger.com
IRS — One Big Beautiful Bill Act: Tax deductions for working Americans and seniors (OBBBA $6,000 senior deduction, phases out above $75K/$150K MAGI). irs.gov

Federal bracket thresholds and standard deductions verified against IRS Rev. Proc. 2025-32 (released October 2025). IRMAA Tier 2–5 surcharge amounts from Kiplinger/CMS 2026 confirmed values; thresholds for Tiers 2–5 are estimates based on announced ranges and may shift slightly when finalized. State income tax rates are approximate and based on typical effective rates on IRA distribution income at pre-retiree income levels. This calculator is for informational purposes only and does not constitute tax advice.