How to Pay Estimated Taxes on a Roth Conversion

To pay estimated taxes on a Roth conversion, calculate the taxable portion of the conversion, add it to your other expected income for the year, and cover the resulting tax through quarterly estimated payments or increased paycheck withholding at a level high enough to meet an IRS safe harbor. For 2026, the IRS charges 7% annual interest on any estimated tax shortfall, so getting the payment amount and timing right protects a meaningful share of the conversion’s long-term benefit.1Internal Revenue Service. Quarterly Interest Rates

Figure Out How Much of the Conversion Is Taxable

If your Traditional IRA holds only pre-tax contributions and their earnings, the entire converted amount is taxable and goes straight onto your ordinary income for the year. It gets more complicated if you’ve made after-tax (nondeductible) contributions, because those dollars have already been taxed. You can’t isolate the after-tax money for conversion. The IRS applies a pro-rata rule that forces every conversion to include a proportional share of both pre-tax and after-tax dollars.2Internal Revenue Service. About Form 8606, Nondeductible IRAs

The pro-rata calculation treats all of your non-Roth IRAs as a single pool: Traditional, SEP, and SIMPLE IRAs combined. The ratio of your total after-tax basis to the combined balance of those accounts, measured as of December 31 of the conversion year, determines what percentage of the conversion escapes tax. If you have $90,000 in pre-tax money and $10,000 in after-tax basis across all your IRAs, 10% of any conversion is a tax-free return of basis. Convert $50,000 and $45,000 is taxable; the other $5,000 is not.

Report the calculation on IRS Form 8606, which is required for any year you execute a conversion.3Internal Revenue Service. Instructions for Form 8606 Failing to file it carries a $50 penalty, and you lose the documentation needed to prove your basis if the IRS ever questions how much of a future distribution is tax-free.

Pay the Tax From Outside Your IRA

When you initiate a conversion, your IRA custodian will offer to withhold federal (and sometimes state) income tax directly from the converted amount. For anyone under 59½, this is a trap. The withheld portion never reaches the Roth, so the IRS treats it as a taxable distribution rather than a conversion. That triggers a 10% early withdrawal penalty on the withheld amount, on top of the regular income tax.4Office of the Law Revision Counsel. 26 U.S. Code 408A – Roth IRAs

Even at 59½ or older, withholding from the IRA still shrinks the amount that lands in the Roth. A $100,000 conversion with 22% withheld puts $78,000 into the Roth and sends $22,000 to the IRS. Those dollars can never grow tax-free. Whenever possible, pay the conversion tax from a taxable brokerage account, savings, or other non-retirement funds so the full conversion amount goes to work inside the Roth.

Quarterly Estimated Payments

You’re required to make estimated tax payments for 2026 if you expect to owe $1,000 or more after subtracting withholding and refundable credits.5Internal Revenue Service. 2026 Form 1040-ES A sizable conversion will almost always clear that bar. The IRS splits the year into four payment periods:

  • Period 1 (Jan 1 – Mar 31): due April 15
  • Period 2 (Apr 1 – May 31): due June 16
  • Period 3 (Jun 1 – Aug 31): due September 15
  • Period 4 (Sep 1 – Dec 31): due January 15 of the following year

When a date falls on a weekend or federal holiday, the deadline shifts to the next business day.6Internal Revenue Service. Estimated Tax Use the worksheet in Form 1040-ES to estimate your full-year liability, including the conversion income, then divide by four for equal quarterly payments.

The IRS accepts estimated payments through Direct Pay (free bank transfer), the Electronic Federal Tax Payment System (EFTPS), and by mailing a check with the Form 1040-ES payment voucher.7Internal Revenue Service. Payments EFTPS requires advance enrollment but offers more scheduling flexibility.

One timing detail matters: estimated payments are credited only on the date they’re actually made. Convert in January and wait until September to pay, and you’ve been underpaid for two quarters. That drives the penalty calculation, which accrues quarter by quarter.

Boost Your W-4 Withholding Instead

If you have a W-2 job, increasing your paycheck withholding is often smarter than sending quarterly checks. Federal income tax withheld from wages is treated as paid evenly across all four quarters, regardless of when it’s actually withheld.8Office of the Law Revision Counsel. 26 U.S. Code 6654 – Failure by Individual To Pay Estimated Income Tax Increase withholding in October and the IRS treats a quarter of that extra withholding as paid in each earlier quarter. No late-payment issue, no underpayment penalty for the earlier periods.

To use this approach, submit a revised W-4 to your employer. Enter the expected conversion tax as extra withholding on line 4(c), or include it as other income on line 4(a) so your employer adjusts automatically. Either way, the extra withholding gets spread across your remaining paychecks. After the conversion year ends, submit another W-4 to drop your withholding back to normal.

This works best when you convert late in the year and still have enough paychecks left to absorb the extra withholding. It also works as a supplement: make estimated payments for most of the tax and use a W-4 adjustment to mop up any shortfall near year-end, with the even-distribution treatment protecting you from a penalty on the earlier quarters.

Safe Harbor Rules That Prevent the Penalty

The IRS imposes a penalty when you don’t pay enough tax throughout the year, calculated on Form 2210. The penalty is essentially interest charged at the federal short-term rate plus 3 percentage points. For early 2026, that rate is 7% annually.1Internal Revenue Service. Quarterly Interest Rates It accrues on each quarter’s shortfall from the payment due date until the tax is paid or the return due date arrives.

You can avoid the penalty by meeting one of two safe harbor thresholds:8Office of the Law Revision Counsel. 26 U.S. Code 6654 – Failure by Individual To Pay Estimated Income Tax

  • 90% of current-year tax. If your combined withholding and estimated payments equal at least 90% of what you owe for 2026, no penalty applies.
  • 100% of prior-year tax. If your payments equal at least 100% of the total tax on your 2025 return, you’re penalty-free regardless of how much you owe for 2026.

The prior-year rule has a catch for higher earners. If your 2025 adjusted gross income exceeded $150,000 ($75,000 if married filing separately), the threshold jumps to 110% of your prior-year tax.9Internal Revenue Service. Underpayment of Estimated Tax by Individuals Penalty

For a large conversion, the prior-year safe harbor is usually the better planning tool. Your 2025 tax is a known number by the time you’re making 2026 payments, so you can calculate exactly what 100% or 110% of that figure is and divide it into four equal installments. Meeting that threshold means the remaining balance from the conversion tax is simply due by the April filing deadline with no penalty attached.

The Annualized Income Installment Method

If your conversion happens late in the year, the standard equal-quarterly-payment approach can feel wasteful because you’re sending large checks in April and June for income you haven’t yet received. The annualized income installment method, reported on Schedule AI of Form 2210, lets you calculate each quarter’s required payment based on the income you actually earned through that period.10Internal Revenue Service. Instructions for Form 2210

Schedule AI divides the year into four cumulative periods ending March 31, May 31, August 31, and December 31. Convert in October and the first three periods show little or no conversion income, so the required installments for those periods drop accordingly. The tax on the conversion concentrates in the fourth-quarter payment instead. Once you elect this method by checking box C on Form 2210, you must use it for all four payment periods on that year’s form.

Other Tax Hits to Build Into Your Estimate

The income from a conversion doesn’t just push you into a higher federal bracket. Several secondary costs move with it, and they should be part of the number you’re paying against.

Medicare Premium Surcharges (IRMAA)

Medicare Part B and Part D premiums are income-adjusted with a two-year lookback. A conversion you do in 2024 determines your premiums in 2026. For 2026, a single filer with modified adjusted gross income above $109,000 (or a joint filer above $218,000) pays higher Part B premiums, and the surcharges climb through five brackets.11CMS. 2026 Medicare Parts A and B Premiums and Deductibles At the top tier, a single filer with income at or above $500,000 pays $689.90 per month for Part B alone, compared to the standard $202.90. Part D prescription drug premiums carry parallel surcharges on the same income tiers.

IRMAA isn’t a tax you send through estimated payments, but it’s a real cost that should factor into whether a conversion makes sense and how large it should be. Splitting a conversion across multiple years to stay below an IRMAA bracket threshold is a common planning adjustment.

Social Security Benefit Taxability

If you’re collecting Social Security, a conversion increases your combined income, which is AGI plus tax-exempt interest plus half your annual benefit. When combined income exceeds $25,000 for a single filer or $32,000 for a joint filer, up to 85% of your Social Security benefits become taxable.12Social Security Administration. Must I Pay Taxes on Social Security Benefits A large conversion can push someone who previously paid no tax on benefits into the maximum 85% taxability tier. That extra taxable Social Security income increases the total tax owed, which has to be reflected in your estimated payments.

Net Investment Income Tax

The 3.8% Net Investment Income Tax applies to the lesser of your net investment income or the amount by which your modified AGI exceeds $200,000 ($250,000 for joint filers).13Internal Revenue Service. Net Investment Income Tax Conversion income itself isn’t classified as net investment income, so it’s not directly subject to the surtax. But the conversion amount increases your modified AGI and can push you over the threshold. If you already have dividends, capital gains, or rental income, a conversion could expose that investment income to an extra 3.8% tax that wouldn’t have applied otherwise. Factor it in if your income is anywhere near those thresholds.

Don’t Forget State Estimated Taxes

Most states with an income tax treat a conversion the same way the federal government does: the taxable portion counts as ordinary income. That means a separate state estimated tax payment may be required alongside your federal payments.

State rules diverge from federal rules in a few ways. The dollar threshold that triggers estimated payment requirements varies widely, from as low as $100 in some states to $1,000 or more in others. Payment due dates don’t always match the federal schedule, so check your state’s tax authority website for the specific deadlines and forms.

Nine states impose no individual income tax and residents can skip this step: Alaska, Florida, Nevada, New Hampshire, South Dakota, Tennessee, Texas, Washington, and Wyoming. Everyone else should build the state tax into the conversion plan from the start. An overlooked state shortfall carries its own penalties and interest, commonly between 4% and 10% annually on the underpayment.