Key Takeaways
- Paying about $60,000 of tax on a $200,000 conversion from a brokerage account leaves the full $200,000 in the Roth, versus $140,000 if the tax is withheld.
- Under age 59 1/2, dollars withheld from a traditional IRA to pay conversion tax face a 10% federal early-withdrawal penalty.
- In 2026, long-term capital gains are taxed at 0%, 15%, or 20%, while traditional IRA withdrawals are ordinary income reaching 37%.
- The safe harbor requires prepaying 90% of the current year’s tax or 100% of last year’s, rising to 110% when prior-year AGI exceeds $150,000.
- Quarterly estimated taxes are generally due April 15, June 15, September 15, and January 15 of the following year.
- Required minimum distributions begin at age 73, or 75 for those born in 1960 or later.
- The 3.8% net investment income tax can apply once MAGI passes $200,000 single or $250,000 joint.
Roth Conversion Tax Figures (2026)
Figures reflect 2026 federal rules described in this article.
The smart way IRA millionaires pay Roth conversion taxes is to fund the tax bill from outside money (a taxable brokerage account or cash) rather than withholding it from the conversion, so the full converted balance keeps compounding tax-free inside the Roth. For holders of $1 million or more in a pre-tax IRA, where the tax money comes from often matters more than which year you convert. Hesitation about the tax bill is one of the Roth conversion myths facing IRA millionaires. Large pre-tax balances also build inside workplace plans, as covered in the tax bill facing 401(k) millionaires.
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Two funding methods exist: pay the tax from outside money, or have the custodian withhold it from the conversion. Paying from outside money is the common default because every converted dollar stays in the Roth and grows tax-free for life. Withholding shrinks the Roth, and under age 59 1/2 the withheld IRA dollars trigger a 10% early-withdrawal penalty. Taxes are generally remitted through quarterly estimates, with a 110% prior-year safe harbor for higher earners.
This guide examines the funding-source question for high-net-worth households. For the broader primer on remittance mechanics, see the sibling article on how to pay Roth conversion taxes, a 2026 strategy guide. For a $1 million-plus IRA, which pocket the tax comes from can change the lifetime result by a wide margin.
Why How You Pay Roth Conversion Taxes Matters More Than When
How you pay Roth conversion taxes often matters more than when you convert because Roth growth is tax-free for life. Two IRA millionaires can owe identical federal tax on the same conversion in the same year, yet finish with very different Roth balances based on one choice: whether the tax came from outside money or from the converted IRA dollars.
Timing gets the most attention in Roth conversion planning, but funding is equally decisive. A Roth grows tax-free for the account holder’s life and, under current inherited-account rules, for up to ten more years after they pass, so every dollar that lands in the Roth at the start compounds untaxed the whole time. Withholding leaves that growth behind; outside money keeps it working.
What Are the Two Ways to Pay Roth Conversion Taxes?
The two ways to pay Roth conversion taxes are paying from outside money or withholding from the conversion. Outside money means cash, savings, or taxable brokerage proceeds, and the full IRA balance converts. Withholding has the custodian remit tax straight from the conversion, so the Roth receives the converted amount minus the tax. Custodians let you elect 10%, 20%, or up to 100% withholding.
Both methods are legal, and both can produce meaningful lifetime tax outcomes compared with never converting. They differ in what reaches the Roth. The table below compares them for a $1 million-plus IRA holder.
| Feature | Pay from outside money | Withhold from the conversion |
|---|---|---|
| Source of tax dollars | Taxable brokerage, savings, or cash | The converting IRA itself |
| Amount landing in the Roth | Full converted balance | Converted balance minus tax withheld |
| Future tax-free growth | Larger base compounding | Smaller base compounding |
| Under age 59 1/2 | No early-withdrawal penalty | 10% penalty on withheld dollars |
| Custodian election | Not applicable | 10%, 20%, or up to 100% |
| Fits when | Outside assets are available | Most assets are locked in the IRA |
Why Does Paying From Outside Money Usually Win?
Paying from outside money usually wins because the full converted balance stays in the Roth and compounds tax-free, while withholding permanently removes the tax dollars from that tax-free base. Consider a $200,000 conversion generating roughly $60,000 of federal tax: paying that $60,000 from a brokerage account leaves the entire $200,000 in the Roth, versus only $140,000 if the tax is withheld.
Picture two retirees with the same age, mix, and returns. Both convert $200,000 in the same year and owe about $60,000 in federal tax. The only difference is funding.
- Retiree A pays the $60,000 from a taxable brokerage account, so the full $200,000 lands in the Roth.
- Retiree B has $60,000 withheld from the conversion, so only $140,000 lands in the Roth.
In year one, both paid the same tax. Retiree A simply has $60,000 more inside an account where future growth is never taxed. Over a long retirement, that head start can grow into a materially larger tax-free balance without taking any additional investment risk, because the account just started larger. The point where the arithmetic turns in your favor is examined in the analysis of the Roth conversion break-even.
Won’t Selling Brokerage Assets Trigger Capital Gains Tax?
Selling appreciated brokerage assets to fund the tax can trigger capital gains, but not all taxes cost the same. Long-term gains on assets held over one year are taxed at 0%, 15%, or 20% in 2026, while traditional IRA dollars taxed later are ordinary income reaching 37%. Paying conversion tax at a 15% or 20% capital gains rate is often cheaper than paying ordinary rates on those IRA dollars later.
This is the tax-bucket arbitrage move. In 2026, the 0% long-term capital gains rate applies to taxable income up to $49,450 for single filers and $98,900 for married couples filing jointly. The 15% rate runs up to $545,500 single and $613,700 joint, and the 20% rate applies above those levels. Ordinary income from a traditional IRA reaches the 37% bracket at $640,600 single and $768,700 joint.
| Income type | 2026 top federal rate | How it stacks |
|---|---|---|
| Long-term capital gains (held over 1 year) | 20% (0% or 15% at lower incomes) | Taxed in a separate lane from ordinary income |
| Ordinary income (traditional IRA withdrawal) | 37% | Adds directly to other ordinary income |
| Short-term capital gains (held 1 year or less) | 37% | Taxed as ordinary income |
The total tax does not disappear; choosing the lower-rate bucket simply leaves more money inside the Roth. Two 2026 surcharges belong in the comparison: the 3.8% net investment income tax can apply to capital gains once modified adjusted gross income passes $200,000 single or $250,000 joint, and Medicare IRMAA surcharges begin above $109,000 single or $218,000 joint MAGI on a two-year lookback. A conversion is taxable ordinary income and is not itself net investment income, though it can push other income into these ranges, so the answer depends on basis, holding period, state, and projected income.
What If I Don’t Have Outside Money to Pay the Tax?
If you do not have outside money, withholding from the conversion is the practical path. Custodians can withhold 10%, 20%, or up to 100% of the conversion for federal tax. The Roth receives less, which reduces future tax-free growth, but the strategy still works. Two cautions apply: a high concurrent withdrawal rate, and any withholding taken before age 59 1/2.
Many IRA millionaires, especially those who rolled a 401(k) into an IRA, hold most of their assets inside the pre-tax account, so withholding is a reasonable route. The withdrawal pace deserves attention: a retiree already drawing 4% to 6% a year for living expenses while also withholding conversion tax can drain the account faster than planned, so many households model the pace across the full horizon.
What Happens If I Withhold Before Age 59 1/2?
Dollars withheld from a traditional IRA to pay conversion tax count as a distribution. Under age 59 1/2, that withheld amount faces a 10% federal early-withdrawal penalty on top of ordinary income tax. The converted balance itself is not penalized, only the portion diverted to the IRS. Younger investors usually fund the tax another way, such as pausing new 401(k) contributions or using a taxable account.
Can a Large Year-End Withholding Fix an Under-Payment?
Yes, for investors age 59 1/2 or older. The IRS treats tax withheld from an IRA as paid evenly across the year, no matter when it actually occurs. A December IRA withholding can therefore retroactively cure an earlier under-payment and satisfy safe harbor, unlike a late quarterly estimate. This makes withholding a legitimate fix, so it is not purely inferior to outside money once the 10% penalty no longer applies.
When Are Roth Conversion Taxes Due, and What Is the Safe Harbor Rule?
Roth conversion taxes are due through the year, not only at filing. Because a conversion is taxable ordinary income, the IRS generally expects quarterly estimated payments on April 15, June 15, September 15, and January 15 of the next year. The safe harbor avoids an underpayment penalty if prepayments cover 90% of the current year’s tax or 100% of last year’s, rising to 110% when prior-year AGI exceeds $150,000.
You can remit the tax three ways: withhold from the conversion, make quarterly estimated payments, or increase withholding on a W-2 or pension. Whichever route you use, the total must reach safe harbor.
- April 15 for the first quarter
- June 15 for the second quarter
- September 15 for the third quarter
- January 15 of the following year for the fourth quarter
The implication for a large conversion year is direct: you can pay the entire tax bill by April 15 and still owe an underpayment penalty if the quarterly payments fell short during the year. Note the exception from the withholding section above: because IRA withholding is deemed paid evenly across the year, it can repair a shortfall that a late estimated payment cannot. A conversion is irreversible and must be completed by December 31, so many households set the estimated-payment schedule before executing, as covered in the guide to the Roth conversion deadline for 2026.
Why Does ‘Convert to the Top of Your Bracket’ Fail IRA Millionaires?
Convert-to-the-top-of-your-bracket advice fails IRA millionaires because a $1.5 million or $3 million IRA barely shrinks under bracket-top conversions, while the unconverted balance keeps growing. Required minimum distributions then force taxable withdrawals at age 73, or 75 for those born in 1960 or later, and a surviving spouse files single at compressed brackets. Lifetime tax, not one year’s bill, is what actually matters.
For a household earning $200,000 with a $400,000 IRA, filling the current bracket may be reasonable. Applied to a seven-figure balance, the same rule leaves the bulk of the account untouched. That balance compounds, and once required minimum distributions begin, they can stack on top of Social Security and pension income at higher rates than a planned conversion would have cost.
A strategic plan weighs several factors instead of a single-year bracket: how aggressively to fill multiple brackets year by year; future events such as RMD onset, Social Security timing, the survivor’s compressed single-filer brackets, and IRMAA thresholds; the full planning horizon rather than the current calendar year; and paying a known ordinary rate now against a likely higher rate later.
The goal is to reduce lifetime tax and improve tax-adjusted net worth: what the account delivers after the IRS takes its share. A $2 million traditional IRA at age 85 is not $2 million of spendable money, and for many IRA millionaires the lifetime picture points toward converting more in lower-income years than bracket-top rules suggest.
Can a Donor-Advised Fund Offset Roth Conversion Taxes?
A donor-advised fund can offset part of a conversion year’s income for households that already give to charity. Instead of donating a set amount each year, the household bunches several years of planned giving into one DAF contribution during the conversion year, claims the larger charitable deduction against the conversion year’s higher income, then grants to charities over time. This move fits established givers, not households opening a DAF solely for the deduction.
The mechanic is bunching. Rather than giving $20,000 a year for five years, a household contributes $100,000 to a DAF in the conversion year, deducts it against the higher income, and grants to chosen charities over the following years. This works only when the philanthropic intent already exists; opening a DAF purely to offset conversion tax rarely makes sense.
What Mistakes Do IRA Millionaires Make Paying Conversion Taxes?
The common mistakes are defaulting to withholding when outside money is available, paying the full bill at filing and still owing an underpayment penalty, withholding from the IRA before age 59 1/2 and triggering the 10% penalty, applying bracket-top rules to a seven-figure IRA, and overlooking state tax. Each one quietly shrinks the Roth or adds avoidable cost.
- Defaulting to withholding when outside money exists. It permanently removes dollars from the tax-free base; outside funding usually keeps more compounding.
- Paying everything at filing. April 15 is the final deadline, not the safe harbor checkpoint. Higher earners need 110% of prior-year tax across the four estimates or face a penalty.
- Withholding under age 59 1/2. Tax withheld from the IRA counts as a distribution, adding a 10% penalty for younger investors.
- Following bracket-top advice on a $1 million-plus IRA. That guidance suits moderate balances and leaves large lifetime tax exposure on a seven-figure account.
- Forgetting state tax. A conversion that pencils out federally can still generate a sizable state bill, which is why some households time large conversions around a move.
Frequently Asked Questions
How do I pay taxes on a Roth conversion?
You pay Roth conversion taxes one of three ways: withhold federal tax from the conversion, make quarterly estimated payments to the IRS, or increase withholding on a W-2 or pension. A conversion is taxable ordinary income, so IRA millionaires converting large amounts often use quarterly estimates funded from outside money and confirm the total meets the safe harbor for the year.
Can I use the converted funds to pay the tax on a Roth conversion?
Yes. The custodian can withhold tax directly from the conversion, but the withheld dollars never reach the Roth and stop compounding tax-free. Under age 59 1/2, those withheld IRA dollars also count as a distribution and face a 10% early-withdrawal penalty. Paying from outside money instead keeps the full converted balance growing tax-free for life.
Is it better to withhold taxes from a Roth conversion or pay from outside money?
For IRA millionaires with taxable brokerage assets or cash, paying from outside money is the common default because the entire converted balance stays in the Roth. Withholding is the practical path when outside money is limited. One nuance: because the IRS treats withholding as paid evenly across the year, a late-year withholding can cure an earlier under-payment for those 59 1/2 and older.
Do I need to make estimated tax payments on a Roth conversion?
Usually yes. A Roth conversion adds taxable ordinary income the IRS expects you to pay throughout the year, not only at filing. If the conversion materially raises income, quarterly estimated payments or extra withholding are generally required. Skipping them can trigger an underpayment penalty even if you pay the full balance by April 15 of the following year.
What is the safe harbor rule for Roth conversions?
The IRS safe harbor avoids an underpayment penalty when your prepayments cover the smaller of 90% of the current year’s tax or 100% of last year’s total tax. For higher earners with prior-year adjusted gross income above $150,000, the prior-year figure rises to 110%. Safe harbor matters most in a large conversion year, when current-year tax spikes sharply.
Is there a penalty for paying Roth conversion taxes at age under 59 1/2?
Yes, if you withhold the tax from the IRA. Dollars withheld from a traditional IRA to pay conversion tax count as a distribution, so under age 59 1/2 they face a 10% federal early-withdrawal penalty plus ordinary income tax. The converted amount itself is not penalized. Younger investors often fund the tax from a taxable account instead.
When are quarterly estimated tax payments due?
Federal quarterly estimated tax payments are generally due April 15, June 15, September 15, and January 15 of the following year. Each payment should reflect income earned in that period, including any Roth conversion completed that quarter. When a deadline falls on a weekend or federal holiday, it shifts to the next business day.
Plan Your Roth Conversion Tax Strategy
Funding a Roth conversion tax bill is a high-impact choice in a multi-year plan, and the right answer turns on each household’s mix of outside assets, age, withdrawal needs, philanthropic intent, and state tax exposure. Because these factors interact, many IRA millionaires model the funding decision alongside the conversion amount rather than settling it in isolation, then revisit it as income changes year to year.
To see how these pieces fit a specific situation, review Q3’s Roth conversion planning service.
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Q3 Advisors is a registered investment adviser focused on retirement tax planning. This page is educational and is not advice; consult a qualified professional.
