Simple math, visible assumptions, clear warnings.

What the Roth conversion calculator does

• Starts with ordinary taxable income before the conversion.
• Adds the taxable portion of the proposed conversion.
• Calculates incremental federal ordinary income tax using a bracket table.
• Shows how much of the taxable conversion lands in each bracket.
• Projects Roth value, traditional value, traditional tax drag, and tax-payment opportunity value by year.
• Compares conversion and no-conversion outcomes through the selected projection period.
• Reports a crossover year when one appears, or says when none appears in the projection.

The two scenarios

In the no-conversion scenario, the selected traditional IRA dollars remain traditional and grow at the entered annual return. The calculator estimates future tax by applying the user-entered future tax rate to that future traditional balance.

In the Roth conversion scenario, the amount reaching Roth grows at the same entered annual return and is shown as after-tax Roth value. If taxes are withheld from conversion funds, the amount reaching Roth is reduced by the estimated current federal tax.

The opportunity cost rule

A Roth conversion tax bill is not economically free just because it is paid from cash outside the IRA. If the conversion does not happen, those outside dollars remain available in the no-conversion scenario. BucketSavers therefore grows the tax-payment dollars at the entered return and shows that opportunity value every year.

If tax is paid from the conversion itself, the model reduces what reaches Roth. The same tax-payment value is still shown so the missing dollars are visible rather than buried.

The calculator also separates the tax-payment drag from the after-tax comparison. Before applying the assumed future tax rate to the traditional IRA, the conversion is behind by the tax-payment dollars and their modeled growth. After the future tax estimate is applied, the conversion may show as ahead in year 1 if the modeled future tax on the traditional balance is larger than the tax-payment opportunity value.

Bracket-fill helper

The bracket-fill helper looks at the selected federal bracket ceiling, subtracts ordinary taxable income before conversion, and translates the remaining taxable room into a gross conversion amount using the taxable percentage entered by the user.

This is only bracket math. It does not know the rest of a tax return, so users should leave room for income surprises, deductions, credits, Medicare premium thresholds, and state tax.

What this version intentionally does not calculate

This version does not model state taxes, Social Security taxation, Medicare IRMAA thresholds, ACA subsidies, capital-gains interactions, tax credits, AMT, NIIT, charitable strategies, estate planning, or year-by-year future tax law changes.

It also does not prepare Form 8606, calculate IRA basis, run the IRA aggregation rule, or evaluate Roth five-year rules. The calculator uses warning messages where those issues may matter instead of pretending to be tax software.

Source review

Current tax-rule references were reviewed against official sources on June 26, 2026:

• IRS Revenue Procedure 2025-32 for 2026 federal tax rate table amounts.
• IRS Revenue Procedure 2024-40 for 2025 federal tax rate table amounts.
• IRS Publication 590-A for traditional-to-Roth conversion income and recharacterization context.
• IRS Publication 590-B for IRA distributions, basis, and Form 8606 context.
• IRS RMD FAQs for required minimum distribution rules.
• Medicare.gov cost information for income-related premium context.