A Roth conversion can create a sizable tax bill, but the cash you need is not simply the conversion amount multiplied by one tax rate. A better estimate starts with the taxable portion of the conversion, measures how much your total federal tax increases with the conversion, adds the incremental state and local tax, and then subtracts extra withholding or estimated payments you already plan to make. Count each tax effect once and budget future Medicare premium changes separately.
This guide focuses on U.S. taxpayers considering a Roth conversion during the 2026 tax year. If possible, estimate the tax before transferring the money and identify where the tax payment will come from. Paying the tax from cash outside the retirement account can allow the full intended conversion amount to reach the Roth account.
What Part of a Roth Conversion Is Taxable?
A Roth conversion moves eligible money from a pre-tax retirement account into a Roth account. The conversion itself does not automatically create a 10% early-distribution tax when completed properly, but the amount that has not already been taxed generally becomes ordinary taxable income for the year of conversion.
The IRS explains that a conversion from a traditional IRA to a Roth IRA generally requires you to include previously untaxed amounts in gross income. See the IRS guidance in Publication 590-A.
If your traditional IRA contains only deductible contributions and investment earnings, the conversion may be fully taxable. A $40,000 conversion from an entirely pre-tax IRA would therefore generally add $40,000 of ordinary income.
After-tax IRA basis changes the calculation
The calculation becomes more complicated if you have previously made nondeductible traditional IRA contributions or rolled after-tax money into an IRA.
You generally cannot choose to convert only the after-tax dollars while leaving all the pre-tax dollars behind. IRS Form 8606 applies aggregation and proportional-taxation rules across applicable traditional, SEP, and SIMPLE IRAs.
The IRS explanation of IRA distributions and basis shows that both the year-end value of your applicable IRAs and distributions during the year can matter when determining the taxable and nontaxable portions.
For a simple screening estimate, you can think of the calculation this way:
Estimated taxable conversion = conversion amount × percentage of your applicable IRA pool that is pre-tax.
For example, suppose your applicable IRA pool consists of $100,000 of pre-tax money and $20,000 of after-tax basis. The pool is approximately 83.33% pre-tax. A $30,000 conversion would therefore be roughly $25,000 taxable and $5,000 nontaxable in a simplified scenario.
To connect that shortcut to year-end records, assume there are no other distributions, contributions, rollovers or value changes. If $30,000 is converted and $90,000 remains in the applicable IRAs at year-end, the simplified denominator is $90,000 + $30,000 = $120,000. The nontaxable share is $20,000 ÷ $120,000, so $5,000 of the conversion is nontaxable and $25,000 taxable. Using only the $90,000 left after conversion would produce the wrong ratio.
Use the Form 8606 instructions for the tax year being filed rather than the shortcut, especially with additional transactions or changing values. Keep basis records for the person who owns the IRA; do not simply combine both spouses' IRAs into one household pool.
How to Use the 2026 Federal Tax Brackets
A common mistake is to look at your current marginal tax bracket and multiply the entire conversion by that percentage. That works only when the entire taxable conversion remains inside one tax bracket and no other tax interactions change.
The federal income tax system is progressive. A large conversion can occupy the remaining space in your current bracket and then spill into one or more higher brackets.
For tax year 2026, the IRS lists the following ordinary-income brackets for single and married-filing-jointly taxpayers. These thresholds apply to taxable income, not gross income or AGI. The IRS 2026 inflation-adjustment guidance provides the official thresholds.
| Rate | Single | Married Filing Jointly |
|---|---|---|
| 10% | $0–$12,400 | $0–$24,800 |
| 12% | $12,401–$50,400 | $24,801–$100,800 |
| 22% | $50,401–$105,700 | $100,801–$211,400 |
| 24% | $105,701–$201,775 | $211,401–$403,550 |
| 32% | $201,776–$256,225 | $403,551–$512,450 |
| 35% | $256,226–$640,600 | $512,451–$768,700 |
| 37% | Over $640,600 | Over $768,700 |
The 2026 basic standard deduction is $16,100 for single taxpayers, $32,200 for married couples filing jointly, and $24,150 for heads of household. If you itemize deductions or qualify for additional deductions, your taxable-income calculation will differ.
The most reliable planning method is therefore:
- Estimate your total federal tax for 2026 without the Roth conversion.
- Recalculate your return with the proposed conversion included.
- Subtract the first tax estimate from the second.
Incremental federal conversion tax = projected federal tax with conversion − projected federal tax without conversion.
This method captures bracket changes much better than multiplying the conversion by your starting marginal rate.
Worked Example: A $60,000 Roth Conversion
Consider an illustrative 2026 scenario. These numbers are hypothetical and are not intended to represent an average taxpayer.
Assume a single taxpayer has $80,000 of taxable income before the conversion and wants to convert $60,000 of fully pre-tax IRA money. Assume for the moment that there are no unusual credits, Social Security interactions, capital-gain complications, or other income-dependent provisions.
The taxpayer begins inside the 22% bracket, which ends at $105,700.
The first $25,700 of the conversion fills the remainder of that bracket:
$25,700 × 22% = $5,654
The remaining conversion is:
$60,000 − $25,700 = $34,300
That portion falls into the 24% bracket:
$34,300 × 24% = $8,232
Total estimated incremental federal income tax:
$5,654 + $8,232 = $13,886
The effective federal tax rate on the $60,000 conversion is therefore approximately 23.1%, even though the conversion starts in the 22% bracket and ends in the 24% bracket.
If this hypothetical taxpayer also expects an incremental state income tax equal to 5% of the conversion, the state estimate would be:
$60,000 × 5% = $3,000
The simplified combined cash estimate becomes:
$13,886 federal + $3,000 state = $16,886
That $16,886 is a planning estimate, not a guaranteed final tax bill. State rules vary, and several federal provisions can make the true incremental cost higher or lower.
Costs That Simple Roth Conversion Tax Math Can Miss
A tax-bracket calculation is a strong starting point, but a Roth conversion raises adjusted gross income and can interact with other parts of the tax system. For some households, those interactions matter more than crossing into the next ordinary-income bracket.
| Issue | Why a Conversion Can Matter | What to Check |
|---|---|---|
| State income tax | The taxable conversion may also be taxable by your state. | State tax rate, retirement-income exclusions, deductions, and residency rules. |
| Social Security taxation | Additional retirement income can cause more Social Security benefits to become taxable. | Your benefits, filing status, other income, and the IRS Social Security worksheet. |
| Senior deduction | A conversion can increase MAGI and reduce an income-limited deduction. | For 2025–2028, the enhanced senior deduction begins phasing out above specified MAGI levels. |
| Marketplace Premium Tax Credit | Higher household income can reduce the credit or increase the amount reconciled on your return. | Your projected full-year household income and Marketplace coverage. |
| Net Investment Income Tax | The conversion itself is generally not net investment income, but the added income can push MAGI over the NIIT threshold and expose existing investment income to the 3.8% tax. | Investment income plus MAGI relative to the applicable NIIT threshold. |
| Medicare IRMAA | A conversion can increase MAGI used for future Medicare Part B and Part D income-related premiums. | Your Medicare status and projected MAGI for the conversion year. |
Social Security can create a hidden marginal-rate effect
The IRS determines the taxable portion of Social Security benefits partly by combining other income with one-half of benefits. As other income rises, more benefits can become taxable, subject to statutory limits. See IRS Publication 915.
That means a $1 increase in Roth conversion income can sometimes increase taxable income by more than $1 because it also causes an additional portion of Social Security benefits to become taxable.
Taxpayers age 65 and older should check the enhanced senior deduction
Under current law, eligible taxpayers age 65 or older may claim an additional senior deduction of up to $6,000 per eligible person for tax years 2025 through 2028. The deduction begins phasing out when modified adjusted gross income exceeds $75,000 for eligible single taxpayers or $150,000 for married couples filing jointly.
Because a taxable Roth conversion raises income, it may reduce this deduction. The IRS summary of the enhanced senior deduction explains the current limits.
Marketplace health-insurance credits require special attention
The IRS specifically identifies taxable IRA and retirement-plan distributions as income changes that can affect the Premium Tax Credit. A Roth conversion can therefore change the amount of subsidy ultimately allowed and potentially increase the amount due when advance credits are reconciled.
For 2026, do not reuse the more generous 2021–2025 eligibility rule. The IRS Premium Tax Credit guidance says the temporary eligibility expansion above 400% of the federal poverty line applied through 2025. For 2026, crossing the applicable household-income ceiling can eliminate the credit. The IRS also states that repayment caps do not apply after 2025: the full excess of advance credits over the final allowed credit must be repaid.
Use your family size and the applicable coverage-year poverty guideline, update the Marketplace with a changed income estimate, and model the final Form 8962 reconciliation. Include that result once in the federal with-and-without-conversion comparison.
A conversion can indirectly increase the Net Investment Income Tax
Retirement-plan and IRA distributions generally are not themselves net investment income for the 3.8% Net Investment Income Tax. However, they are taken into account when determining whether MAGI exceeds the NIIT threshold.
That means a conversion can potentially cause more of your existing interest, dividends, capital gains, rental income, or other net investment income to become subject to the tax. The IRS lists NIIT thresholds of $200,000 for single and head-of-household filers and $250,000 for married couples filing jointly. See the IRS Net Investment Income Tax guidance.
Medicare IRMAA may show up later rather than on this year's tax return
Social Security generally uses tax-return information from two years before a Medicare premium year when determining the income-related monthly adjustment amount, or IRMAA. For example, 2026 Medicare premiums generally use 2024 tax information.
Following that normal two-year lookback, a Roth conversion completed in 2026 could affect Medicare income-related premiums in 2028. However, 2028 IRMAA thresholds and premium amounts are not yet known, so do not use the 2026 threshold table as though it were a confirmed 2028 table. See the Social Security Administration's Medicare premium guidance.
A Practical Roth Conversion Cash-Reserve Worksheet
Instead of asking, “What percentage should I set aside?” build the reserve from the tax return upward.
| Step | Amount |
|---|---|
| 1. Projected federal tax after applicable credits and additional taxes, without conversion, before withholding and estimated payments | $_____ |
| 2. Projected federal tax on the same basis, with conversion, before withholding and estimated payments | $_____ |
| 3. Incremental federal tax: Step 2 − Step 1 | $_____ |
| 4. Incremental state and local tax, calculated with and without the conversion | $_____ |
| 5. Extra withholding or estimated payments allocated to this incremental conversion tax | $_____ |
| Estimated remaining current-year tax reserve: Steps 3 + 4 − 5 | $_____ |
Avoid double counting: Steps 1 and 2 should model the complete federal result, including income-sensitive deductions, credits, Premium Tax Credit reconciliation and any additional taxes that apply. If a lost deduction, reduced credit or NIIT increase is already included in that comparison, do not add it again. Apply the same principle to the state calculation. Compare tax liability before withholding and estimated payments, not a refund or balance-due figure that already deducts those payments.
Hypothetical worksheet check: Suppose the complete federal comparison shows a $14,000 increase, already including a $500 credit reduction. State tax increases by $3,000, and $4,000 of extra payments is allocated to the conversion. The remaining tax reserve is $14,000 + $3,000 − $4,000 = $13,000. Adding the $500 credit reduction again would incorrectly produce $13,500.
The worksheet isolates the additional reserve caused by the conversion. If the no-conversion projection already shows an unpaid balance, budget that separately too. Do not allocate the same withholding or estimated payment to both the baseline liability and the conversion.
Future Medicare IRMAA premiums are a separate cash-flow item for the relevant premium year; they are not an extra line in this current-year tax-reserve calculation. Keep any uncertainty buffer separate too. If the result is negative, check the payment assumptions rather than treating it as a guaranteed refund or instruction to reduce a required payment.
If your income is uncertain, you may choose to hold an additional cash cushion above the calculated amount. Keep that planning buffer separate from the actual estimated tax so you know which number represents expected liability and which represents uncertainty protection.
The most useful question is not “Is 25% enough?” It is “How much larger is my projected total tax liability after I add this conversion to my actual 2026 return?”
How to Pay the Tax During the Year
Estimating the conversion tax and satisfying the federal pay-as-you-go rules are related but separate tasks.
The IRS generally requires estimated payments when you expect to owe at least $1,000 after withholding and refundable credits and those payments will not satisfy the applicable required-payment threshold.
For most taxpayers, the federal underpayment safe harbor is based on the smaller of:
- 90% of the tax expected on the current year's return; or
- 100% of the prior year's tax.
If your prior-year AGI exceeded $150,000, or $75,000 if married filing separately, the prior-year percentage generally becomes 110%. See IRS Publication 505 for 2026 withholding and estimated-tax rules.
The safe harbor does not tell you the economic cost of the Roth conversion. It primarily helps determine whether enough tax has been prepaid to avoid an underpayment penalty. You can satisfy a safe harbor and still owe a substantial balance when filing your return.
Depending on your circumstances, you may cover the additional liability through estimated tax payments, increased withholding from wages or pensions, or a combination of the two. State estimated-payment rules should be checked separately.
The payment dates matter too
For most calendar-year taxpayers, the regular 2026 federal estimated-payment due dates are April 15, June 15 and September 15, 2026, and January 15, 2027, subject to applicable exceptions or relief. A large payment at filing time does not automatically cure an earlier installment shortfall.
If a conversion occurs late in the year, review the annualized-income installment method rather than assuming the tax must be spread as though the conversion happened in January. Publication 505 explains how uneven income is handled. Federal withholding is generally treated as paid in equal shares across the payment periods, unless actual withholding dates are used; estimated payments are credited when paid. This difference can matter when choosing how to cover a late-year conversion. Confirm the required amount and timing for the whole return, and check state rules separately.
Be careful about withholding tax from the IRA itself
Using retirement money to pay the tax changes the economics of the conversion.
Suppose you request a $50,000 IRA distribution but have $10,000 withheld for federal taxes and only $40,000 reaches the Roth. The $10,000 withheld is not sitting inside the Roth account. Depending on your age and circumstances, an amount kept out of the conversion can also create an early-distribution issue.
If that entire $50,000 distribution is pre-tax, the ordinary-income calculation generally starts from $50,000, not only the $40,000 deposited into the Roth. The $10,000 withheld is a tax prepayment. If you are under age 59½, the $10,000 not converted could also produce a $1,000 additional early-distribution tax unless an exception applies. Withholding itself does not establish your final tax bill.
The IRS states that an IRA distribution paid to you is generally subject to 10% withholding unless you elect otherwise, while trustee-to-trustee transfers can avoid withholding. Properly converted amounts are generally not subject to the 10% early-distribution tax merely because the conversion occurs before age 59½, but money distributed and not converted may face different treatment.
If the money is coming from a former employer plan rather than an IRA, withholding mechanics can differ. A distribution from an employer retirement plan paid directly to you can generally be subject to 20% mandatory withholding, while a qualifying direct rollover avoids that withholding. For the broader account-choice issues, see our guide to 401(k) rollover vs leaving money in an old plan.
Special Cases to Check Before Converting
You have nondeductible IRA basis
Locate your prior Forms 8606 before estimating the tax. Missing basis records can make the conversion calculation substantially less reliable.
You are already subject to required minimum distributions
A required minimum distribution for a particular year cannot itself be converted to a Roth IRA. The RMD and any additional conversion therefore need to be modeled separately. The IRS discusses this limitation in Publication 590-A.
You expect a large capital gain, bonus, business profit, or RSU income
Model the conversion with the additional income included. A conversion that appears to fit neatly inside one bracket early in the year may spill into a substantially higher bracket after later income is added.
You are considering converting before year-end without knowing your final income
Roth conversions completed in tax years beginning after 2017 generally cannot be recharacterized back into a traditional IRA. In other words, you should not assume that you can simply reverse a conversion next spring if the tax bill is larger than expected.
This is one reason some taxpayers use partial conversions rather than moving an entire large pre-tax balance at once when their full-year income remains uncertain.
Pre-Conversion Checklist
- Estimate your 2026 income before the conversion. Include wages, pensions, taxable Social Security, interest, dividends, business income, capital gains, and other taxable items.
- Estimate your taxable income after deductions. Tax brackets apply to taxable income, not gross income.
- Determine how much of the proposed conversion is actually taxable. Check Form 8606 history and all traditional, SEP, and SIMPLE IRAs if you have after-tax basis.
- Calculate federal tax both ways. Compare a return without the conversion to a return with the conversion.
- Add state and local tax. Use your state's actual retirement-income rules rather than assuming every state treats conversions identically.
- Check income-sensitive items. Review Social Security taxation, the senior deduction, Premium Tax Credit, NIIT, Medicare IRMAA exposure, and any other credit or deduction tied to income.
- Review what has already been prepaid. Count current withholding and estimated payments before deciding how much additional cash must be sent to tax authorities.
- Choose the source of the tax payment. Understand the consequences before withholding tax directly from retirement assets.
- Check the conversion mechanics. Confirm whether the transaction is an IRA conversion, direct plan-to-Roth rollover, or distribution paid to you.
- Keep records. Retain Forms 1099-R, 5498, 8606, conversion confirmations, basis records, and estimated-tax payment confirmations.
Set Aside Cash From the Complete Tax Projection
The best estimate of Roth conversion taxes is the difference between your projected tax return with the conversion and your projected return without it.
Start by identifying the taxable portion of the conversion. Apply the 2026 tax brackets to your full projected income rather than multiplying the conversion by one rate. Then add state tax and examine income-sensitive items such as Social Security taxation, deductions, health-insurance tax credits, NIIT, and future Medicare IRMAA.
Finally, compare the resulting liability with the withholding and estimated payments you are already making. That gives you a much more useful answer to the practical question: How much cash should I have available before I complete this Roth conversion?
Educational note: This article provides general educational information and is not individualized tax, investment, or legal advice. Roth conversion results can vary significantly with filing status, IRA basis, state residence, deductions, credits, retirement benefits, investment income, and other transactions. Consider using current tax software or a qualified tax professional when a conversion is large enough to materially change your tax return.
