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Roth conversion tax calculator: what a conversion will cost
Estimate the federal tax on a Roth conversion, and how much fills a bracket, step by step with a worked example in this year's brackets.
Education, not advice. This page explains general rules with invented examples. It isn't financial, tax or legal advice for your situation. Tax figures are for 2026 and come from published IRS, SSA and CMS sources. Rules change, so check current figures before you act.
A Roth conversion moves money from a pre-tax account, such as a traditional IRA, into a Roth IRA. The amount you convert is taxable income this year. This page shows how to estimate that tax, and how much you can convert before you reach the next bracket.
The formula
- Add up this year's income without the conversion: pensions, wages, interest, dividends, taxable withdrawals and the taxable part of Social Security.
- Subtract your deductions to get taxable income. Most retirees use the standard deduction plus the extra amount for age 65 and older.
- Find the top of the bracket you want to fill. The conversion that reaches it is the bracket's top minus your taxable income.
- Work out the tax with and without the conversion. The difference is the cost of the conversion.
Converted dollars are taxed at your marginal rate. So as long as a conversion stays within one bracket, its tax is simply the amount times that bracket's rate.
2026 federal brackets, single filers
| Rate | Taxable income from | Up to |
|---|---|---|
| 10% | $0 | $12,400 |
| 12% | $12,400 | $50,400 |
| 22% | $50,400 | $105,700 |
| 24% | $105,700 | $201,775 |
A worked example
Linda is 66, single and retired. She plans to claim Social Security at 70. This year she has $45,000 of pension and interest income. Her deductions are the standard deduction, the extra amount for age 65, and the senior deduction available through 2028.
| Step | Amount |
|---|---|
| Income without a conversion | $45,000 |
| Standard deduction | $16,100 |
| Extra for age 65 or older | $2,050 |
| Senior deduction | $6,000 |
| Taxable income without a conversion | $20,850 |
| Top of the 12% bracket | $50,400 |
| Conversion that fills the bracket | $29,550 |
| Federal tax without the conversion | $2,254 |
| Federal tax with the conversion | $5,800 |
| Cost of the conversion | $3,546, or 12% |
Her income including the conversion is $74,550. That stays just under the $75,000 point where the senior deduction starts to shrink. Going past it would add hidden tax, because the deduction phases out by 6% of the excess.
What a simple calculation leaves out
A one-year estimate tells you the cost today. Whether the conversion pays off depends on the years ahead:
- Your future tax rate. Conversions pay off when the rate you avoid later, on required distributions or in your heirs' hands, is higher than the rate you pay now.
- Thresholds beyond the brackets. Extra income can raise Medicare IRMAA premiums two years later, reduce an ACA premium tax credit before 65, or make more Social Security taxable.
- State tax, which may add several percent.
- Paying the tax. Paying from savings outside the IRA keeps more in the Roth. Withholding from the conversion shrinks it, and before age 59.5 the withheld part may face a penalty.
- Many years at once. The right amount this year depends on what you'll convert in later years.
The app's Taxes screen tests conversion plans across your whole projection: a fixed amount, filling a chosen bracket, or an optimizer's year-by-year schedule. It can hold conversions under IRMAA tiers, the ACA cliff and the net investment income tax threshold. It compares lifetime taxes and what's left after tax.
Frequently asked questions
Can I undo a Roth conversion?
No. Recharacterizing a conversion back to a traditional IRA hasn't been allowed since 2018. Size each conversion carefully.
Does a conversion count as my RMD?
No. In a year you owe a required distribution, take it first. You can convert more after that.