Roth conversion tax calculator (2026)

Last reviewed September 2026 · 6 min read

A Roth conversion moves money from a traditional IRA or 401(k) into a Roth account. The IRS treats the converted amount as a distribution from the traditional account that is immediately rolled into the Roth: it is includible in your gross income as ordinary income for the year you convert, and the 10% early-withdrawal tax does not apply to the conversion itself^[1]. You are, in effect, paying tax now to buy tax-free growth and withdrawals later.

Marginal vs. effective — and why they diverge

A conversion is taxed like any other ordinary income: it stacks on top of your other income and fills brackets from the bottom up. If the whole conversion fits inside one bracket, your marginal rate and your effective rate on the conversion are the same number. Convert enough to spill into the next bracket, though, and the effective rate — total extra tax ÷ conversion amount — sits between the two brackets, closer to whichever one absorbed more of the dollars. That is the number that actually tells you what the conversion cost.

“Fill the bracket” sizing

A common way to size a conversion is to convert only up to the top of a chosen bracket — 12%, 22%, 24%, or 32% are the usual targets^[5] — so you know in advance the exact marginal rate you are paying, then stop. The calculator below shows the “room left” in whatever bracket the conversion currently reaches, so you can dial the conversion amount to that boundary instead of guessing at a round number.

Three cautions before you convert

Three things this federal-tax number does not capture, each worth its own read:

• IRMAA’s two-year lookback. A large conversion raises this year’s MAGI, and Medicare prices Part B/D surcharges off the tax return from two years earlier — see IRMAA: the Medicare surcharge with a two-year memory for the current tiers and how a conversion at 63 can raise premiums at 65.
• ACA subsidy MAGI. If you buy Marketplace coverage before 65, the same conversion income counts toward premium-tax-credit MAGI and can shrink or eliminate a subsidy — see The ACA subsidy cliff after 2025.
• The 5-year clock on the converted principal. Converting does not itself trigger the 10% penalty, but if you withdraw the converted amount within five taxable years (and are under 59½, with no exception), the 10% additional tax applies to that conversion’s taxable portion in the year you take the early withdrawal^[2] — not back-dated to the conversion year itself, but a real cost that only shows up if you tap the money too soon. That’s a separate clock from the one that governs tax-free earnings. See The three 5-year rules of Roth accounts and the Roth conversion ladder for how a multi-year ladder is built around it.

State income tax is not included anywhere on this page — see state taxes on retirement income for how much that can add or, in a handful of states, subtract.

Pay the tax from cash, not the conversion

If a large conversion pushes this year’s bill well above what withholding covers, quarterly estimated payments may be required: the safe harbor is the lesser of 90% of this year’s tax or 100% of last year’s (110% if last year’s adjusted gross income was over $150,000)^[4]. Paying the conversion’s tax from a separate taxable account — instead of withholding it from the conversion itself — also means the full converted amount lands in the Roth. See avoiding the estimated-tax underpayment penalty for the mechanics.

What this calculator ignores

This is a federal-ordinary-tax-only estimate. It does not include state income tax, the 3.8% net investment income tax (conversions themselves are not NII, but they can push other investment income over its threshold), how the conversion can pull more of your Social Security into taxation, or how it stacks under capital gains and qualified dividends that might otherwise sit at 0%. It also does not add the 65-or-older additional standard deduction or the temporary OBBBA senior deduction — see 2026 federal tax brackets and standard deductions for those figures, which this repo’s simulator engine does not model either^[3].

Try it in Deorbit Plan

This calculator answers “what does converting $X cost this year?” A single year rarely tells the whole story — the payoff shows up over a decade of avoided RMDs and Medicare surcharges. Open the Strategy panel and set Conversion strategy to Fill bracket (retired years) to model a multi-year conversion ladder with IRMAA and RMDs included, run across your own income path instead of one static year.

Educational content only — not financial, tax, or investment advice.

See how this plays out with your own numbers. Try it in the simulator →