Roth Conversion Calculator

This Roth conversion calculator estimates the federal tax cost of converting traditional IRA or 401(k) funds to Roth this year, using your real marginal tax bracket — then compares the long-term after-tax value of converting versus leaving the money traditional.

Worked example (the defaults): converting $50,000 on top of $80,000 of existing taxable income, filing single, under 2026 tax brackets. That conversion costs $11,486 in federal tax — an effective rate of 22.97% on the converted amount, since it's taxed at your marginal rate but blended across whichever brackets it pushes you through. The conversion pushes your top marginal rate to 24%. Grown at 7% annually for 20 years, the converted Roth balance reaches $149,037 tax-free, versus $147,048 if the same $50,000 had stayed traditional and been taxed at withdrawal at today's marginal rate.

That comparison is close in this example precisely because the conversion pushed the person into a materially higher bracket — the math favors conversion more clearly when you convert in a lower-income year. Already required to take distributions? RMDs can't be converted to Roth — check the RMD Calculator first for what's mandatory before deciding what additional amount to convert voluntarily.

A Roth conversion adds the converted amount to your ordinary taxable income for the year, per IRS guidance on Roth IRAs. The tax cost isn't a flat rate — it's the difference between two full bracket calculations:

This matters because a conversion can straddle multiple brackets — the first dollars converted might be taxed at your current marginal rate, while later dollars in a large conversion push into the next bracket up. The "effective rate on conversion" this calculator shows is the blended rate across whatever brackets the conversion actually spans, which is usually different from — and can be higher than — your marginal rate before converting.

Roth conversions generally work best in years when your taxable income is unusually low — early retirement before Social Security and RMDs begin, a career gap, or a low-income year for any reason. Converting in a low bracket now, to avoid a higher bracket later (from RMDs, for instance), is the core strategic logic. Converting in a high-income year, as in the default example above, still grows tax-free forever, but the upfront tax cost eats into the advantage.

Two things this calculator doesn't model: state income tax (which applies to the conversion in most states) and Medicare IRMAA surcharges, which can be triggered by a large conversion pushing your income above certain thresholds two years later. Both are worth checking with a tax professional before converting a large amount in a single year — spreading a big conversion across multiple years (a "conversion ladder") is a common way to manage both issues.