There is no legal limit on how much you can convert to a Roth IRA. You can move $5,000, $500,000, or your entire traditional retirement balance in a single year, and the IRS won’t stop you. What decides the practical ceiling is the tax bill: every pre-tax dollar you convert lands on your return as ordinary income for the year, and a big conversion can trigger secondary costs that don’t show up until later.
Contribution Limits Don’t Apply to Conversions
The annual limits people associate with Roth IRAs govern new money going in. For 2026, that’s $7,500, or $8,600 if you’re 50 or older.1Internal Revenue Service. Retirement Topics – IRA Contribution Limits A conversion is a different transaction. You’re moving money that already sits inside a retirement account rather than adding new savings, and the IRS places no ceiling on that movement. A $2 million traditional IRA can be converted in one shot if you’re willing to pay the taxes.
The same freedom applies to traditional IRAs, SEP IRAs, and SIMPLE IRAs. Conversions also sit outside the one-per-year IRA rollover rule, which normally limits you to a single IRA-to-IRA rollover in any 12-month period.2Internal Revenue Service. Rollovers of Retirement Plan and IRA Distributions You could convert three separate traditional IRAs to Roth IRAs in the same month without a problem.
No Income Restriction Either
Direct Roth contributions phase out at higher incomes. For 2026, single filers lose eligibility between $153,000 and $168,000 of modified adjusted gross income, and joint filers between $242,000 and $252,000.1Internal Revenue Service. Retirement Topics – IRA Contribution Limits Earn above those thresholds and direct contributions are off the table.
Conversions have no such restriction. Congress removed the old $100,000 income cap on Roth conversions through the Tax Increase Prevention and Reconciliation Act of 2005, effective for tax years beginning after December 31, 2009.3The United States Senate Committee on Finance. Background on the Roth IRA Conversion Proposal in Tax Reconciliation Bill Whether you earn $40,000 or $4 million, you can convert any amount. That change is what makes the “backdoor Roth” strategy possible for high earners.
How the Tax Works
The converted amount is added to your ordinary income for the year the conversion is completed. If you’re converting pre-tax money — deductible traditional IRA contributions plus all the investment growth — every dollar is taxable. The conversion stacks on top of your wages, business income, and investment earnings, and it’s taxed at your marginal rate.
For 2026, federal brackets for single filers start at 10% on the first $12,400 of taxable income and climb to 37% above $640,600. Joint filers hit 37% above $768,700.4Internal Revenue Service. IRS Releases Tax Inflation Adjustments for Tax Year 2026, Including Amendments From the One, Big, Beautiful Bill A conversion doesn’t get taxed at a single flat rate. It fills your brackets upward from wherever your other income leaves off. If your salary already puts you at the top of the 24% bracket, the first dollar of your conversion is taxed at 32%. That’s why the amount you should convert usually isn’t “all of it.”
You don’t owe the 10% early withdrawal penalty on a conversion, even under age 59½. The IRS treats a conversion as a rollover rather than a premature distribution.5Internal Revenue Service. Retirement Topics – Exceptions to Tax on Early Distributions A separate five-year recapture rule can bring that penalty back if you withdraw the money too soon, covered further down.
Most states treat Roth conversions the same as ordinary taxable income. State rates range from zero to over 13% for high earners in a handful of states. In a high-tax state, the combined federal and state marginal cost on a large conversion can push past 40%.
After-Tax Money Converts Tax-Free
If you’ve made non-deductible contributions to a traditional IRA, that basis has already been taxed. Converting it again wouldn’t be fair, and the IRS agrees: the after-tax portion converts tax-free. The problem is figuring out what percentage of any given conversion qualifies.
The Pro-Rata Rule Decides What’s Taxable
Under 26 U.S.C. § 408(d)(2), the IRS treats all of your traditional, SEP, and SIMPLE IRA balances as one combined pool when calculating the taxable portion of a distribution or conversion.6Office of the Law Revision Counsel. 26 U.S. Code 408 – Individual Retirement Accounts You can’t pick which dollars move.
An example. You have $80,000 in a traditional IRA from deductible contributions and growth, plus $20,000 of non-deductible contributions in a separate traditional IRA. Total: $100,000, with $20,000 of after-tax basis, or 20%. Convert $50,000 and 20% of it ($10,000) is tax-free, while 80% ($40,000) is taxable income. Isolating the $20,000 non-deductible IRA and converting it “clean” is not an option the IRS recognizes.
The pro-rata calculation uses the total value of all your traditional IRA accounts as of December 31 of the conversion year, not the balance on the day you convert. A rollover you make in November can change the tax treatment of a conversion you did in March. Tracking your basis requires the running history from IRS Form 8606.7Internal Revenue Service. Instructions for Form 8606 If you made non-deductible contributions but never filed the form, reconstructing that history from old returns and Form 5498 statements is worth doing, because without it you may end up paying tax on money that was already taxed.
The 401(k) Workaround
Pro-rata only aggregates IRA accounts. Employer plans, 401(k)s, 403(b)s, and 457(b)s sit outside the calculation. If large pre-tax IRA balances are contaminating your pro-rata math, rolling those pre-tax dollars into your current employer’s 401(k), assuming the plan accepts incoming rollovers, removes them from the IRA pool. That leaves only your non-deductible basis in the IRA, which you can convert with little or no tax. Converting directly from a 401(k) to a Roth IRA also sidesteps pro-rata, because the rule applies only to IRA-to-IRA transactions.
Costs a Large Conversion Can Trigger
The marginal rate on the conversion itself isn’t the whole picture. A big conversion raises your MAGI, and several other taxes and premiums move with MAGI.
Net Investment Income Tax
The 3.8% Net Investment Income Tax applies to the lesser of your net investment income or the amount your MAGI exceeds $200,000 (single) or $250,000 (joint).8Internal Revenue Service. Topic No. 559, Net Investment Income Tax The conversion itself isn’t investment income, but it lifts your MAGI. If you also have capital gains, dividends, or rental income in the same year, the conversion can push that investment income into NIIT territory it wouldn’t have otherwise reached.
Medicare Premium Surcharges
Medicare Part B and Part D premiums are based on MAGI from two years earlier. A large conversion in 2026 raises premiums in 2028. For 2026, the first IRMAA surcharge kicks in at $109,000 for single filers and $218,000 for joint filers, adding $81.20 per month to Part B. At the top tier ($500,000 single, $750,000 joint), the surcharge reaches $487.00 per month per person.9Centers for Medicare & Medicaid Services. 2026 Medicare Parts A and B Premiums and Deductibles Part D carries its own separate IRMAA surcharge on top.
Social Security Taxation
Up to 85% of Social Security benefits become taxable once combined income (adjusted gross income, plus non-taxable interest, plus half your Social Security) exceeds $34,000 for single filers or $44,000 for joint filers. Those thresholds haven’t changed since 1993, so most retirees with any meaningful conversion are already above them. Even a modest conversion can flip Social Security from partially taxable to fully taxable at the 85% cap.
The Five-Year Recapture Rule
Converting sidesteps the 10% early withdrawal penalty at the moment of conversion. But if you’re under 59½ and pull the converted money out of the Roth within five years, the IRS imposes that 10% penalty on the portion of the conversion that was taxable, effectively recapturing what you avoided.10Internal Revenue Service. Publication 590-B – Distributions From Individual Retirement Arrangements (IRAs)
Each conversion has its own clock, starting January 1 of the tax year the conversion occurred. Convert $50,000 in October 2026 and the five-year window runs from January 1, 2026 through December 31, 2030. Reach 59½ during that period and the recapture penalty drops away, because the age exception overrides it. If you don’t plan to touch the money for decades, this rule is a non-issue. If early access is part of the plan, track each conversion’s clock separately.
A Conversion Cannot Be Reversed
Before 2018, a Roth conversion could be undone through recharacterization if the market dropped or the tax bill turned out larger than expected. The Tax Cuts and Jobs Act permanently eliminated that option for conversions completed on or after January 1, 2018.11Internal Revenue Service. Retirement Plans FAQs Regarding IRAs Once you convert, you own the tax consequences. There is no path back to the traditional IRA. That makes sizing the conversion correctly the first time more important than it used to be.
Spreading Conversions Across Years
Because a conversion fills your brackets upward, the practical answer to “how much can I convert” for most people is “as much as fits inside a bracket you’re comfortable paying.” Take a $500,000 traditional IRA held by someone whose ordinary income normally sits at the top of the 24% bracket. Converting the whole balance in one year pushes much of it into 32% or 35%. Converting $100,000 a year over five years keeps more of the money in lower brackets. The math is straightforward: figure out how much headroom you have in your current bracket, convert up to that amount, and repeat next year.
The same logic applies in reverse for the secondary costs. If a conversion of a certain size would tip you across an IRMAA threshold or a NIIT threshold, shrinking the conversion just below that line often saves more than the additional tax-deferred growth would earn.
Paying the Tax and Meeting the Deadline
A Roth conversion must be completed by December 31 of the year you want it to count. This differs from regular IRA contributions, which run to the April tax-filing deadline. A 2026 conversion has to be in the Roth account by December 31, 2026.
The IRS imposes an underpayment penalty if you haven’t paid at least 90% of your current-year tax liability, or 100% of last year’s liability, whichever is smaller, through withholding and estimated payments by year-end.12Internal Revenue Service. Topic No. 306, Penalty for Underpayment of Estimated Tax You can ask your IRA custodian to withhold federal tax from the conversion itself using Form W-4R, but every dollar withheld is a dollar that doesn’t reach the Roth and doesn’t grow tax-free. The alternative is quarterly estimated payments from outside funds, which keeps the full conversion amount working inside the Roth. When converting from a 401(k), a direct trustee-to-trustee rollover avoids the mandatory 20% federal withholding that applies to distributions paid to you.2Internal Revenue Service. Rollovers of Retirement Plan and IRA Distributions