Federal Tax · 2025
Roth Conversion Tax Calculator
Enter your current income and a conversion amount to see exactly what a Roth IRA or 401(k) conversion costs in federal taxes — with a bracket-stacking visualization showing where the converted dollars land, how much spills into the next bracket, and the incremental tax the conversion triggers.
Your scenario
Gross income — standard deduction is applied automatically
The amount being converted from Traditional IRA / 401(k) to Roth
Chart legend
Informational only — not professional tax advice.
Enter your current income and conversion amount to see exactly where the converted dollars land in the bracket stack — and what incremental tax they trigger.
Methodology
How the tax cost is computed
The calculator runs the 2025 federal income tax computation twice using IRS Rev. Proc. 2024-61 brackets — once on your base income, and once on base income plus the Roth conversion amount. Both computations apply the standard deduction for your filing status. The incremental tax is the difference: what you owe with the conversion minus what you owe without it.
The bracket-stacking chart shows every bracket reached by your income or conversion, with existing income filling the bracket bar in blue and conversion dollars filling on top in orange. Brackets the conversion does not touch are dimmed. Hovering or reading the right column shows the exact dollar amount in each bracket and the tax it generates.
Formula
taxable_base = max(0, gross_income − standard_deduction) taxable_after = max(0, gross_income + conversion − standard_deduction) tax_before = apply 2025 brackets to taxable_base tax_after = apply 2025 brackets to taxable_after incremental_tax = tax_after − tax_before effective_rate = incremental_tax ÷ conversion_amount Bracket stacking per bracket [min, max]: existing_in_bracket = min(taxable_base, max) − min(taxable_base, min) after_in_bracket = min(taxable_after, max) − min(taxable_after, min) conversion_in_bracket = max(0, after_in_bracket − existing_in_bracket)
Tax year scope
Brackets cited to IRS Rev. Proc. 2024-61 (2025 tax year brackets). Roth conversion treatment: IRC §408A(d)(3) and IRS Publication 590-A — conversions from a Traditional IRA are included in gross income in the year of conversion and taxed as ordinary income.
Stated assumptions and limitations
- Federal income tax only. Most states also tax Roth conversions as ordinary income. Your total tax cost including state income tax will be higher.
- IRMAA not included. If you are on Medicare or will be in two years, the conversion may increase your income above IRMAA thresholds, triggering higher Part B and Part D premium surcharges. These are not shown here.
- No 10% early withdrawal penalty. If you are under age 59½ and convert funds that have not been in the Roth for 5 years, the 10% penalty on early distributions may apply. Consult IRS Publication 590-B.
- Standard deduction only. This calculator applies the standard deduction. If you itemize, enter your AGI after itemized deductions in the gross income field for a more accurate result.
- Conversion amount increases MAGI. If you are in an IRA deductibility phase-out range, a Roth conversion phase-out range, or subject to the NIIT (Net Investment Income Tax), higher income from the conversion may have additional effects this tool does not capture.
Last reviewed: January 2025. Brackets are updated annually following IRS Rev. Proc. announcements (typically November).
Frequently asked questions
Why do Roth conversions increase my tax bill?
A Roth conversion is treated as ordinary income in the year you convert. The converted amount is added to your other income and taxed at your marginal federal income tax rates. The benefit comes later: once in a Roth IRA, the money grows tax-free and qualified withdrawals in retirement are never taxed again. The conversion is essentially a bet that paying taxes now (at your current rates) is cheaper than paying taxes later (at future rates, which may be higher). The tax cost shown here is the 'price of admission' to tax-free Roth growth.
When is a Roth conversion most tax-efficient?
The best time to convert is when your income — and therefore your marginal tax rate — is temporarily lower than usual: early in retirement before Social Security begins, in a year with large deductions, or after a business loss. The bracket-stacking chart helps you identify how much conversion 'fits' in a lower bracket before spilling into the next one. For example, if your existing taxable income fills the 12% bracket partially, you can convert exactly enough to fill it before tipping into the 22% bracket — a strategy called 'bracket topping.'
Does a Roth conversion affect Medicare premiums (IRMAA)?
Yes. Medicare Part B and Part D premiums use IRMAA surcharges based on your Modified Adjusted Gross Income (MAGI) from two years prior. A Roth conversion increases your MAGI in the conversion year, which can trigger higher Medicare premiums two years later. The 2025 IRMAA surcharges begin at $106,000 MAGI (single) and $212,000 (MFJ). This tool computes the federal income tax cost only — IRMAA surcharges are a meaningful additional cost for Medicare-age converters that is not reflected here.
Should I withhold taxes from the conversion or pay from savings?
Paying the tax from separate taxable savings — rather than having taxes withheld from the converted amount — is almost always the better choice. If you withhold taxes from the conversion, that portion never makes it into the Roth account, reducing the amount of money that can grow tax-free. If you're under 59½, the withheld amount is also treated as an early withdrawal subject to the 10% penalty. The incremental tax shown here is the amount you'd ideally pay from non-IRA savings to maximize the after-tax value of the conversion.
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