Roth Conversion Tax Implications

A Roth conversion moves retirement money from a traditional account into a Roth account. You generally pay ordinary income tax on the pre-tax portion in the year of the conversion. Money you already paid tax on—properly tracked after-tax basis—is not taxed twice.

The useful question is not just “What tax bracket am I in?” It is “What changes on my whole return if I convert this amount?” A conversion can cross tax brackets, reduce a health-insurance credit or affect a later Medicare premium.

Jump to: income-tax examples · after-tax basis · 2026 ACA ceiling · Medicare · paying the bill · tax forms.

Federal tax: a conversion fills brackets in layers

Ordinary federal income-tax rates in 2026 are 10%, 12%, 22%, 24%, 32%, 35% and 37%. Moving into a higher bracket does not reprice all your earlier income at that rate. Each slice is taxed in its own bracket.

Start with income before the conversion, add the taxable conversion, then account for deductions. Taxable income—not gross wages or the account balance—is what you compare with the ordinary-income brackets. Capital gains, credits and income-sensitive deductions can complicate the calculation.

One person, four possible conversion amounts

Assume Alex is single, under 65, has $80,000 of wages in 2026 and no other income, adjustments, credits or special deductions. Alex uses the $16,100 standard deduction. Before converting, taxable income is $63,900. Every conversion dollar in this example is pre-tax.

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For the $50,000 conversion, Alex has $41,800 left in the 22% bracket: $105,700 − $63,900. The remaining $8,200 falls in the 24% bracket. So the added tax is ($41,800 × 22%) + ($8,200 × 24%) = $11,164, not $50,000 multiplied by one rate.

These are bracket-formula estimates, not completed tax returns; IRS tax-table rounding can differ. They exclude state tax, credits, Medicare premiums and other income effects. The brackets and standard deduction come from the IRS's 2026 inflation adjustments.

After-tax basis: the part you do not pay tax on twice

A nondeductible traditional IRA contribution creates basis: money that has already been subject to income tax. Form 8606 tracks it. If your traditional IRA money mixes pre-tax dollars and basis, you usually cannot choose to convert only the after-tax dollars.

The pro-rata calculation generally combines the same owner's traditional IRAs, traditional SEP IRAs and traditional SIMPLE IRAs across custodians. It uses the year-end value together with the relevant distributions and conversions during that year. A spouse's IRAs and workplace-plan balances are not part of that owner's IRA pool. Special adjustments can apply.

That differs from converting an entire $50,000 IRA pool containing $10,000 of basis: with no other relevant balances or transactions, $40,000 would be taxable. Do not apply that whole-account shortcut to a partial conversion. See the pro-rata guide and Form 8606 instructions.

ACA Marketplace coverage: the 2026 income ceiling is back

If you buy health insurance through the Marketplace, the premium tax credit can help pay your premiums. The temporary removal of its 400%-of-poverty income ceiling applied to 2021–2025. It does not extend to 2026 under current law. For 2026, household income above that ceiling means no federal premium tax credit.

For 2026 coverage, use the applicable 2025 poverty guideline, not the new 2026 guideline. For a one-person household in the contiguous states and DC, that is $15,650. Four times that amount is $62,600. Alaska and Hawaii have different guidelines, and larger households have different limits.

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The household might lose a credit as well as owe ordinary tax on the conversion. There is no universal dollar cost: it depends on the actual credit, premiums, household and coverage months. Being below the ceiling does not guarantee a credit or preserve its earlier amount.

ACA household income generally combines modified adjusted gross income for the tax filer, spouse and dependents required to file. For this test, MAGI starts with AGI and adds specified excluded foreign income, tax-exempt interest and nontaxable Social Security benefits. A taxable Roth conversion is included. The standard deduction does not reduce this income measure.

Advance credits need a second check. For tax years after 2025, the income-based caps on repayment of excess advance premium tax credits are removed. If too much credit is paid in advance, the excess generally must be repaid in full. Report income changes to the Marketplace and model the final annual household income before converting.

Sources: IRS premium tax credit overview, IRS premium tax credit FAQ and HealthCare.gov poverty guidelines. These are federal credit rules, not a statement that all state assistance ends.

Medicare: a conversion can affect premiums two years later

IRMAA is an extra charge added to Medicare Part B and Part D premiums when income is above certain levels. It is not a tax on the Roth account. Social Security generally uses a tax return from two years earlier to decide whether you owe it.

That means a 2026 conversion generally affects 2028 premiums if you are enrolled then. The 2028 table is not yet published. Do not treat today's thresholds as an exact future bill.

For 2026 premiums, the standard tier ends at $109,000 of IRMAA MAGI for an individual return and $218,000 for a joint return. The first higher tier runs above those amounts through $137,000 and $274,000, respectively. A special schedule applies to married people filing separately who lived together during the tax year. IRMAA MAGI generally means AGI plus tax-exempt interest.

One high-income tax year generally maps to one premium year. It does not create a lifetime surcharge by itself. Repeated high-income years can create repeated charges. Coverage months, which parts each person has, and any qualifying appeal matter.

Use the IRMAA Trap Detector for a year-by-year check. Published amounts: CMS's 2026 Medicare premium tables.

Social Security: why the extra tax can exceed your bracket

A taxable conversion can make more of your Social Security benefits taxable. The income test includes other income, certain adjustments and tax-exempt interest, plus half your Social Security benefits. Depending on that calculation, up to 85% of benefits can be included in taxable income. That is not an 85% tax rate.

During part of this phase-in, another $1 of conversion income can bring another $0.85 of benefits into taxable income. If that entire $1.85 falls in the 22% bracket, the added federal tax is $1.85 × 22% = $0.407: an effective marginal rate of 40.7% on that next conversion dollar.

This is a limited interaction, not a new statutory bracket and not a rate to multiply by every dollar of a large conversion. Once 85% of benefits is already taxable, there is no further Social Security inclusion to add. Use IRS Publication 915 to calculate the actual benefit inclusion.

NIIT: the conversion is excluded, but other investment income can be exposed

The 3.8% net investment income tax, or NIIT, generally applies to the smaller of net investment income or the amount MAGI exceeds the relevant threshold. The threshold is $200,000 for single filers and $250,000 for married filing jointly.

Retirement-plan distributions covered by IRC §1411(c)(5), including IRA conversions, are excluded from net investment income. But a taxable conversion can raise MAGI and expose more of your other investment income.

For example, a married couple filing jointly has $220,000 of wages and $50,000 of net investment income, with no other relevant adjustments. Their $270,000 MAGI exceeds the $250,000 threshold by $20,000, producing $760 of NIIT. A fully taxable $100,000 conversion raises MAGI to $370,000. NIIT is then 3.8% of the full $50,000 investment-income amount: $1,900, an increase of $1,140. That is an indirect cost, not NIIT charged directly on the conversion.

Source: IRS NIIT questions and answers.

State tax: federal basis and state basis can differ

A state may tax conversions differently from the federal return, exclude certain retirement income or recognize a different amount of already-taxed IRA contributions. New Jersey is a useful example of why a federal taxable amount is not automatically the state taxable amount. Start with the New Jersey guide and the state's IRA worksheet rather than applying a flat percentage to the federal number.

If you are moving, establish the actual residency timeline. There is no universal “spend 183 days there” shortcut. A move can change which state taxes covered retirement income, but domicile, part-year rules and each state's law matter. The California and Pennsylvania guides explain different state systems. Do not assume a proposed move creates a guaranteed conversion-tax saving.

Paying the tax: withholding is not money converted

If your traditional IRA sends $50,000 out but withholds $11,000 for tax, only $39,000 reaches the Roth. Assuming the entire distribution is pre-tax, all $50,000 is still income-taxable. The $11,000 withheld is a payment toward the eventual tax bill, not a guarantee that the bill equals $11,000.

If you are under 59½ and no exception applies, that $11,000 not converted can also create a $1,100 early-distribution additional tax. Withholding did not make that portion a conversion.

Using outside cash for the tax can let the entire $50,000 reach the Roth and avoid that particular early-distribution issue. But outside cash also has a job: reserves, other goals or investments. Selling assets to raise it can itself create tax. Compare the full trade-off rather than assuming outside funding is always best.

See how to pay taxes on a Roth conversion. Conversions made after 2017 cannot be undone by recharacterizing them back to traditional IRAs; confirm the tax cost before completing the transaction.

Estimated payments: when the tax needs to be paid

The income tax belongs to the conversion year, but waiting until the filing deadline to pay it can lead to an underpayment penalty. Withholding and timely estimated payments count toward the required payments.

For most taxpayers, the required annual payment is the smaller of 90% of current-year tax or 100% of prior-year tax. The prior-year percentage becomes 110% if prior-year AGI exceeded $150,000, or $75,000 for married filing separately. The prior-year return must cover 12 months. Special rules apply to some taxpayers.

These safe harbors address an underpayment penalty, not the final tax bill. Payment timing still matters. A late-year conversion may call for the annualized-income method; withholding generally has different timing treatment from an estimated payment made near year-end. Review IRS Publication 505 or the tax-year Form 2210 instructions before relying on a catch-up payment.

A lower-income year can help—but check more than the bracket

Suppose James is single, 58 and has no other income in 2026. A fully taxable $50,000 conversion minus the $16,100 standard deduction leaves $33,900 of taxable income. The bracket-formula estimate is:

• First $12,400 at 10%: $1,240.
• Remaining $21,500 at 12%: $2,580.
• Total: $3,820, before credits, state tax and tax-table rounding.

That is not a 22% conversion. But if James has Marketplace coverage, the conversion also enters his ACA income calculation. A low ordinary-income-tax estimate is not proof of a low total cost.

A bracket-filling example works the same way: with $30,000 of ordinary income and the $16,100 deduction, taxable income starts at $13,900. The 12% bracket ends at $50,400, leaving $36,500 of room. Under these simplified assumptions, a fully taxable $36,500 conversion adds $4,380 of ordinary income tax. It can still affect a credit or another income test.

Do not treat an age range as an automatic conversion window. Someone born in 1971 is 55 in 2026 and reaches required-minimum-distribution age at 75 under current law, not 73. The years before required distributions may be worth modeling, but no fixed lifetime saving follows from that timeline alone.

Three other interactions worth checking

After a spouse dies

A survivor may eventually move from joint brackets to narrower single brackets, subject to the rules for the year of death and any qualifying-surviving-spouse status. In 2026, $150,000 of taxable income on a joint return is in the 22% bracket, while $110,000 of taxable income on a single return is in the 24% bracket. Those are taxable-income figures, not IRMAA income thresholds. Future household income and benefits can also change; model them rather than assuming everything stays the same.

Qualified business income deduction

Conversion income is not qualified business income. But it can raise the income used to test the deduction's limitations, potentially reducing a business owner's deduction. The result depends on the business type, income, wages and other details. Do not reuse an old phaseout range; see the IRS qualified business income guidance.

Assets left to heirs

Many inherited taxable assets receive a basis adjustment generally tied to value at death. Pre-tax IRA income does not receive that same step-up; it is generally income in respect of a decedent. Existing nondeductible IRA basis is different and can still matter. Inherited Roth earnings are tax-free only when the applicable qualification requirements are met. These differences belong in an estate comparison, but they do not by themselves prove that converting now will save a family money.

Sources: IRS Publication 559 and inherited Roth tax rules.

Form 8606: three parts, not four

For a traditional-IRA-to-Roth conversion, the relevant Form 8606 sections are:

• Part I: nondeductible traditional IRA contributions and the basis/pro-rata calculation when required.
• Part II: conversions from traditional IRAs to Roth IRAs.
• Part III: distributions from Roth IRAs, not the incoming conversion itself.

There is no Part IV. A direct employer-plan-to-Roth-IRA rollover has different reporting instructions; do not assume every transaction involving Roth uses Part II. Keep Forms 1099-R and 5498, prior basis records and transaction confirmations. A custodian may not know your basis held elsewhere.

The latest final Form 8606 instructions reviewed here are for 2025. Use the 2026 form and instructions when available for a 2026 return. If required distributions apply, the required amount is not eligible for conversion; separate it from any amount you intend to move to Roth.

A practical before-and-after check

1. Calculate the taxable conversion using your actual basis and full IRA pool.
2. Compare the return without the conversion and with it—not just the top bracket.
3. Check ACA household income, the later Medicare premium year, Social Security taxation, NIIT and relevant deductions.
4. Add state treatment and decide how and when the tax would be paid.
5. Compare a smaller conversion and no conversion as well as the amount you first considered.

The conversion cost calculator can help frame the comparison. Review its assumptions and omissions; a calculator estimate is not a completed tax return.

Rules and examples checked August 31, 2026. Federal bracket amounts are from the IRS's 2026 guidance. Medicare examples use the published 2026 premium table only. Sources are linked beside each topic. All worked examples are hypothetical and omit changes not expressly stated.

Frequently asked questions

Do you owe taxes on a Roth conversion?

Generally, the pre-tax portion is ordinary income in the conversion year. Properly allocated after-tax basis is not taxed again. The amount actually converted is not subject to the 10% early-distribution tax, but money withheld or otherwise kept out of the Roth may be subject to that tax before age 59½ unless an exception applies.

Does a Roth conversion trigger IRMAA Medicare surcharges?

The taxable portion can. A 2026 conversion generally affects the income used for 2028 Medicare premiums if you are enrolled then. The 2028 table is not yet published. One high-income tax year generally maps to one premium year, not a lifetime surcharge.

Can a Roth conversion remove an ACA premium tax credit in 2026?

Yes. The temporary removal of the 400%-of-poverty income ceiling applied through 2025, not 2026. For 2026 coverage, the ceiling for a one-person household in the contiguous states and DC is $62,600. A taxable conversion can push household income above it; other eligibility conditions also apply.

Should I pay the conversion tax from outside funds?

Using outside cash can keep more of the distribution in the Roth and avoid an early-distribution penalty on tax money withheld from an IRA. But compare cash reserves, borrowing costs and any tax from selling other assets. It is not an automatic recommendation for every household.

When is the best time to convert?

There is no universal best age or year. Lower-income years can offer room, but the comparison must include ordinary tax, ACA credits, later Medicare premiums, state rules and other income-sensitive items. A smaller conversion or no conversion can be reasonable.

What if I can't afford to pay the conversion tax?

Work out the tax and payment timing before moving money. A smaller conversion, a later conversion or leaving the money in the traditional account may fit better. Do not assume the income tax can wait until filing or that a completed conversion can simply be reversed.