Can You Do a Prior Year Roth Conversion? Rules and Tax Impact

You cannot do a prior year Roth conversion. A conversion counts in the tax year the money actually leaves your traditional, SEP, or SIMPLE IRA, and federal tax law offers no way to backdate that transfer or apply it to a year that has already closed.¹ If the December 31 deadline passed, the earliest you can convert is this year, and the taxable income from that conversion will appear on this year’s return.

The Calendar Year Rule

The date that matters is when funds leave the traditional account, not when you file your return or when you first decided to convert. Funds that leave a traditional IRA on January 2 belong on the new year’s return, even if you intended the conversion for December. There is no filing-season grace period and no election on Form 8606 that shifts a conversion backward.

Financial institutions can take several business days to process a conversion request. A request submitted on December 30 does not guarantee that the transaction settles before year-end. If you want a conversion to land in a particular tax year, the transfer itself has to be complete by December 31 of that year.

Why IRA Contributions Can Be Backdated but Conversions Cannot

This is where most of the confusion comes from. IRA contributions follow a more generous timeline: you have until the tax filing deadline, typically April 15, to make or designate a contribution for the prior year.² A deposit made in March 2027 can still count as a 2026 contribution. Conversions get no such extension.¹

The split shows up sharply in the backdoor Roth strategy. If you make a prior-year nondeductible contribution to a traditional IRA in early 2027 and immediately convert it, the contribution goes on your 2026 tax forms while the conversion appears on your 2027 return. Both steps are legitimate. They simply live on different years’ filings.

What to Do If You Missed December 31

If the deadline passed, your strategy is not lost — it is delayed by one year. A conversion completed this year will be taxed as this year’s income. A few practical points shape whether you should go ahead now or wait for a better moment:

Income can vary. If you expect this year’s ordinary income to be lower than next year’s (a gap between jobs, a sabbatical, an early retirement year before Social Security begins), converting now may cost less in tax than waiting.
There is no income limit on conversions. The Roth contribution phaseouts — $153,000 to $168,000 for single filers and $242,000 to $252,000 for married couples filing jointly in 2026 — do not apply. Regardless of adjusted gross income, you may convert amounts from a traditional IRA to a Roth IRA.³⁴
There is no cap on how much you can convert. You can convert $10,000 or $1,000,000 in the same year, though the full taxable portion hits your return in the year of conversion.
If you are 73 or older, take your required minimum distribution before converting. An RMD cannot itself be converted; it must be withdrawn as a distribution first, and failing to take the full RMD can trigger a penalty of up to 25%, reduced to 10% if corrected within two years.⁵

Executing the Conversion So It Settles in Time

To avoid a repeat of last year’s timing problem, start the request well before December. You can convert traditional IRA funds using any of three methods:¹

A trustee-to-trustee transfer, where your traditional IRA custodian sends the funds directly to your Roth IRA provider. This is the simplest approach and avoids handling a check yourself.
A same-trustee transfer, where both accounts sit at the same institution and the custodian moves funds internally. This usually settles fastest.
A 60-day rollover, where you receive a distribution and have exactly 60 days to redeposit it into a Roth IRA. Miss the window and the distribution becomes permanently taxable, plus a 10% early withdrawal penalty if you are under 59½.⁶

IRA distributions are not subject to the 20% mandatory federal withholding that applies to distributions from 401(k)s and other employer plans. Custodians often offer optional withholding, sometimes defaulting to 10%, but you can decline it so the full amount reaches your Roth.⁷

The Tax Bill You’ll Owe This Year

A conversion adds the taxable portion of the converted amount to your ordinary income for the year. If your traditional IRA holds only nondeductible contributions, the conversion is mostly tax-free. If it holds any deductible contributions or earnings, the pro-rata rule applies: you cannot choose to convert only the after-tax dollars.⁸

The math: divide your total nondeductible contributions (your basis) by the combined December 31 value of every traditional, SEP, and SIMPLE IRA you own. That fraction is the nontaxable share of your conversion. The rest is taxable income. The IRS aggregates all of these accounts, including an old rollover IRA at another brokerage.⁹

You report the conversion on Form 8606, which establishes your basis and calculates the taxable amount that flows to your Form 1040.¹⁰ If you have made nondeductible contributions over the years without tracking basis on Form 8606, the IRS can treat the entire conversion as taxable, so keep records of every nondeductible contribution.

Estimated Tax Payments

If the conversion creates a tax bill of $1,000 or more above what withholding and credits cover, you generally need estimated tax payments to avoid an underpayment penalty.¹¹ You can avoid the penalty by paying at least 90% of your current-year liability or 100% of the tax shown on last year’s return, rising to 110% if your prior-year adjusted gross income exceeded $150,000.¹² A late-year conversion may qualify for the annualized income installment method on Form 2210, which shows no estimated payment was due in earlier quarters.

Ripple Effects on Other Income-Based Costs

A conversion raises your modified adjusted gross income, and several thresholds react to that number:

The 3.8% Net Investment Income Tax applies once MAGI exceeds $200,000 for single filers, $250,000 for married couples filing jointly, or $125,000 for married filing separately. Those thresholds are not inflation-adjusted. Conversion income itself is not net investment income, but a higher MAGI can pull your other investment income into the surtax.¹³
Medicare Part B and Part D premiums use MAGI from two years prior. A large 2026 conversion can raise 2028 premiums through the Income-Related Monthly Adjustment Amount.
Most states with an income tax treat conversion income the same as other taxable income, with rates that can exceed 13% in some states.

Spreading conversions across multiple years is a common way to keep any single year’s income below the brackets and thresholds that hurt the most. It also chips away at future required minimum distributions, since Roth IRAs are not subject to RMDs during the owner’s lifetime.⁵

Once Converted, You Cannot Undo It

Before 2018, you could recharacterize a conversion, essentially reversing it and moving the money back to a traditional IRA if the account dropped in value or the tax bill was larger than expected. The Tax Cuts and Jobs Act eliminated that option. Any conversion completed on or after January 1, 2018, is permanent and cannot be recharacterized.¹ The same prohibition applies to amounts rolled from a 401(k) or 403(b) into a Roth IRA.

Each conversion also starts its own five-year clock. If you withdraw converted amounts within five years and you are under 59½, the taxable portion of the conversion is subject to a 10% early withdrawal penalty.¹⁴ Because you cannot walk it back and the tax is locked in the moment funds move, model your expected tax liability before initiating the conversion rather than after.

The short version: last year’s window closed on December 31 and cannot be reopened. Set a reminder to start this year’s conversion by early December so processing time does not push it into another calendar year, and run the pro-rata math and MAGI effects before you send the request.

1
Internal Revenue Service. Retirement Plans FAQs Regarding IRAs
2
Internal Revenue Service. IRA Year-End Reminders
3
Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500
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Internal Revenue Service. Topic No. 309, Roth IRA Contributions
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Internal Revenue Service. Retirement Plan and IRA Required Minimum Distributions FAQs
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Internal Revenue Service. Rollovers of Retirement Plan and IRA Distributions
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eCFR. 26 CFR 31.3405(c)-1 – Withholding on Eligible Rollover Distributions
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Internal Revenue Service. Publication 590-B, Distributions From Individual Retirement Arrangements
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Internal Revenue Service. Instructions for Form 8606
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Internal Revenue Service. About Form 8606, Nondeductible IRAs
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Internal Revenue Service. Estimated Taxes
12
Internal Revenue Service. Estimated Tax
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Internal Revenue Service. Questions and Answers on the Net Investment Income Tax
14
Office of the Law Revision Counsel. 26 USC 408A – Roth IRAs