Roth conversion tax calculator 2026

What a conversion costs

Moving money from a traditional IRA to a Roth IRA does not cost a fee; it costs income tax. You pay that tax now so that qualified withdrawals later are tax-free. The question is whether the rate you pay today is lower than the rate you would pay later. This calculator answers the first half: the exact federal tax for the amount you choose, using the 2026 brackets for your filing status.

How it is calculated

The tax on the conversion is the tax on (taxable income + conversion) minus the tax on taxable income, both from the 2026 tax rate tables in IRS Revenue Procedure 2025-32. Because the brackets are progressive, a conversion that starts inside the 12% bracket and ends in the 22% bracket is taxed partly at each rate; the table shows the slice and the tax in each. The effective cost is the tax divided by the amount converted, and it is also the break-even future rate in the sense described above (our derivation).

Worked example

A single filer has $40,000 of taxable income. The tax on that is $4,552. Converting $20,000 makes it $60,000, with a tax of $7,912, so the conversion costs $3,360: $10,400 at 12% ($1,248) and $9,600 at 22% ($2,112). That is 16.8% of the amount converted, and the filer ends in the 22% bracket. These are example numbers, not typical ones.

Limits of this method

• Federal ordinary income tax only. State income tax, the net investment income tax, the taxation of Social Security benefits and the phase-out of deductions and credits all react to higher income and are not in the figure.
• Income-tested programs. A conversion can raise Medicare IRMAA premiums two years later and affect the Marketplace premium tax credit, which uses modified AGI. We do not compute either because their thresholds depend on the year and your household.
• It cannot be reversed. A conversion made after 2017 cannot be recharacterized (Publication 590-B). If the market falls right after you convert, the tax is still due on the amount converted.
• Pro-rata. If you hold pre-tax and after-tax money in IRAs, only part of a conversion is tax-free, based on all your IRAs at year-end.
• Taxable income must be right. A higher taxable income estimate before the conversion makes the conversion cost more. Include all other income, and deductions you will actually take.

How is a Roth conversion taxed?

The amount you convert from a traditional IRA is added to your income for the year, except for any part that is your after-tax basis (see the pro-rata rule). The IRS treats the conversion as a distribution that you roll into a Roth IRA, so it is included in gross income. On Form 8606 the taxable amount of a conversion (Part II, line 18) is carried to line 4b of Form 1040. The extra income is taxed at ordinary rates, stacked on top of the rest of your taxable income, so it fills the brackets from the bottom of your current bracket upward. In 2026 a single filer with $40,000 of taxable income who converts $20,000 pays $3,360 on it, 16.8% of the amount.

What is the difference between marginal and effective cost?

The marginal rate is the rate on the last dollar of the conversion: 22% in the example. The effective cost is the average rate on the whole conversion, which is lower when the conversion starts in a lower bracket: $10,400 is taxed at 12% and $9,600 at 22%, so the average is 16.8%. Planners often convert only up to the top of the current bracket so that no dollar is taxed at the higher rate. In the example $10,400 fits before the 12% bracket ends at $50,400, and converting just that costs $1,248, 12%.

How do I know if converting is worth it?

The usual reasoning compares the tax rate you pay now with the rate you expect to pay when you would otherwise withdraw. If you expect a higher rate later, converting now saves tax; if a lower rate, waiting does. The break-even future rate in this calculator is the effective cost of the conversion (16.8% in the example). At an expected 24% later, converting costs $3,360 now against $4,800 later on the same $20,000, a difference of $1,440. This is our derivation: it assumes you pay the tax from money outside the IRA, ignores growth and any change in the law, and treats tax rates as the only difference. Tax-free growth and no required minimum distributions from a Roth IRA owned by you can add to the case, and paying the tax out of the IRA itself takes away from it.

Can I undo a conversion?

No. Under current law a conversion cannot be recharacterized (returned to a traditional IRA): IRS Publication 590-B says that a conversion or rollover to a Roth IRA made in tax years beginning after December 31, 2017 cannot be recharacterized. Plan on the conversion being final, and pay attention to the amount before you make it, not after the market moves.

What are the five-year rules?

There are two separate five-year periods in IRS Publication 590-B. First, a distribution from a Roth IRA is qualified (tax-free) only if it is made after the five-year period starting with the first tax year for which you made a contribution to any Roth IRA of yours, and it is also made on or after age 59½, because of disability, to a beneficiary after death, or for a first home (up to $10,000). Second, if you take out converted money within five years starting on January 1 of the year of the conversion, the part you had to include in income is generally subject to the 10% additional tax on early distributions unless an exception applies; each conversion has its own five-year period. The second rule matters mainly if you are under 59½.

What about Medicare premiums and health insurance subsidies?

A conversion raises your adjusted gross income, and income is used in other programs, which this calculator does not compute. Medicare charges higher premiums (the income-related monthly adjustment amount, IRMAA) to higher earners, and the SSA and Medicare say it is generally based on your tax return from two years earlier, so a conversion in one year can show up in premiums two years later. For Marketplace premium tax credits, the IRS defines household income as modified AGI, so the taxable part of a conversion counts; the eligibility range and repayment rules have changed in recent years, so check the IRS premium tax credit page for the current year. Also watch the taxation of Social Security benefits and state income tax. We have not included any of these thresholds because they change and depend on your situation.

Should I pay the tax from the converted money?

You can, but it shrinks what lands in the Roth and, if you are under 59½, the part withheld is itself a distribution that may be subject to the 10% additional tax. In the example, a $20,000 conversion with the $3,360 tax taken from it leaves $16,640 in the Roth IRA. Paying the tax from a bank account keeps the whole $20,000 working in the Roth, which is why the break-even above assumes outside money. Ask your tax preparer about withholding and estimated tax payments for the year.

Does the tax year matter?

Yes. This calculator uses the 2026 brackets from IRS Revenue Procedure 2025-32 (for a single filer, 10% to $12,400, 12% to $50,400, 22% to $105,700) and takes the taxable income you enter as given. Count the conversion in the year you do it, not the year you file. The same $50,000 conversion on top of $60,000 of taxable income for a married couple filing jointly costs $6,920 (13.8%).

Estimates for planning only — not tax or financial advice; your tax return and a tax professional decide. Sources, checked October 28, 2026: IRS Revenue Procedure 2025-32, section 4.01 (tax rate tables); IRS Publication 590-B (2025), chapters 1 and 2 (conversions, five-year rules, no recharacterization); Instructions for Form 8606 (2025), Part II; SSA POMS HI 01101.031 (IRMAA); IRS Premium Tax Credit overview. Related: Roth IRA calculator, traditional IRA calculator, RMD calculator, income tax calculator and IRA pro-rata calculator. How we check our calculators.