Roth conversion deadline: why December 31 is the date that counts

The rule: the distribution date sets the tax year

Under IRC §408A(d)(3), a traditional-to-Roth conversion is treated as a distribution from the traditional IRA followed by a rollover into the Roth IRA, and the taxable part is included in gross income. The timing comes from Treasury Regulation §1.408A-4, A-7: the converted amount is includible in income "for the taxable year in which the amount is distributed or transferred from the traditional IRA." For individuals on a calendar year, the last day to create 2026 conversion income is December 31, 2026.

The same regulation (A-1) lists three ways to switch an IRA to a Roth: a trustee-to-trustee transfer to a Roth IRA at another custodian, a transfer to a Roth IRA at the same custodian (including simply redesignating the account), or a distribution to you that you roll into a Roth IRA within 60 days. In every case the custodian reports it on the Form 1099-R for the year the money left the account, and you report it in Part II of Form 8606 for that same year. The same calendar logic governs a 401(k)-to-Roth IRA rollover or an in-plan Roth conversion.

For the broader mechanics (cost, pro-rata rule, whether to convert at all), start with our Roth conversion guide. This page is about the calendar.

Roth conversion deadline vs. contribution deadline: 2026 dates

The dates below all hang off one decision made by December 31. Weekdays are for the 2026–2027 calendar.

Why April 15 does not apply to conversions

The IRA calendar runs on two clocks. Regular contributions get the extra time: IRS Publication 590-A lets you make a 2026 contribution up to the original due date of your 2026 return, April 15, 2027. For 2026 the limit is $7,500, plus a $1,100 catch-up at age 50 and over, per the IRS's 2026 limits announcement. Conversions have no annual limit and no carry-back: the deadline to convert a traditional IRA to a Roth for 2026 is December 31, 2026, and a conversion completed on January 4, 2027 is a 2027 conversion.

This produces a split that catches people running a backdoor Roth. You can make a nondeductible 2026 contribution in March 2027 and convert it the same week, but the conversion is a 2027 event. It lands on the 2027 Form 8606, and the pro-rata calculation uses the value of all your traditional, SEP and SIMPLE IRAs as of December 31, 2027 (line 6 of Form 8606). Anyone clearing out pre-tax IRA balances first, for example by rolling them into an employer plan, needs that done by December 31 of the year they convert.

Custodian cutoffs and the last week of December

Because the regulation keys on when the amount is distributed or transferred, the controlling fact is your custodian's processing date, which is what the 1099-R will reflect. A request placed online on December 30 that the custodian processes on January 4 is a 2027 conversion. Several mechanics make the last week risky:

• The calendar. December 31, 2026 is a Thursday and January 1 is a market and bank holiday, so there is no buffer day.
• Published cutoffs. Custodians commonly publish a year-end deadline for conversion requests that falls before December 31, earlier still for paper forms or manual handling. Get your custodian's date in writing.
• In-kind conversions. Converting securities is allowed, taxed at fair market value on the date of transfer. Listed securities move quickly; private funds, notes and other alternative assets in a self-directed IRA need a current valuation and custodian sign-off, which can take weeks.
• Transfers between firms. A trustee-to-trustee transfer to a Roth IRA elsewhere depends on both firms; open the receiving account in November.
• The 60-day route. A December distribution deposited in a Roth IRA in January is still taxed in the distribution year under §1.408A-4, A-7, but it adds reporting friction and 60-day risk. A same-custodian conversion is cleaner.

A workable pattern: settle the amount by early December, submit by mid-December, and keep room for a small top-up if year-end numbers come in low. When the 1099-R arrives, check Box 7 against our guide to Roth conversion 1099-R codes.

No recharacterization: the deadline is also a commitment

Before 2018, a conversion could be recharacterized back to a traditional IRA as late as the extended due date of the return, which made an early-year conversion close to a free option. The Tax Cuts and Jobs Act closed that. Section 408A(d)(6)(B)(iii), added by Pub. L. 115-97 §13611, removes conversions from the recharacterization rule, and the Form 8606 instructions say plainly that a conversion made in tax years beginning after December 31, 2017 "cannot be recharacterized." Regular contributions can still be moved between IRA types; conversions cannot, a distinction our recharacterization guide walks through.

So December 31 is not only the last day to convert, it is the last day to get the number right. If the market falls afterward, you owe tax on the higher value; if a late bonus or K-1 lifts your income, the conversion is taxed at the higher rate. Neither can be fixed after the fact.

RMD years: take the RMD before you convert

Once you reach your RMD age, there is an ordering rule. Regulation §1.408A-4, A-6 says an amount must be eligible for rollover before it can be converted, required minimum distributions are not eligible, and the first dollars distributed in an RMD year are treated as the RMD until the full amount has come out. Convert first and the portion that should have been your RMD is treated as a regular contribution to the Roth IRA, which is typically an excess contribution that has to be corrected.

So the year-end sequence for anyone in an RMD year (age 73 for those reaching it in 2026) is: take the full RMD, then convert. The 2026 RMD and the 2026 conversion share the same December 31 deadline, which compresses the year-end window further. The year you turn 73 has an extra wrinkle, because the first RMD can be delayed to April 1 but must still be satisfied before any conversion that year; our page on whether a Roth conversion counts as an RMD covers that trap and how to repair a conversion made in the wrong order.

What a $50,000 conversion costs in 2026

The cost of a year-end conversion is the federal tax on $50,000 of extra ordinary income stacked on top of everything else on the return, using the 2026 brackets in Rev. Proc. 2025-32. Four illustrative filers, each converting $50,000 of fully pre-tax money in December 2026, after the standard deduction and before state tax:

The same $50,000 costs anywhere from $6,920 to $15,316 in federal tax depending on what it sits on top of, which is why the conversion decision is a bracket decision. The table also understates the cost for anyone near a threshold: it ignores state income tax, the 3.8% net investment income tax that the extra MAGI can switch on for other income, the two-year IRMAA lookback and, for filers 65 and older with MAGI under about $250,000 joint, the $6,000 senior deduction (IRC §151(d)(5), tax years 2025 through 2028), which shrinks by 6 cents for every dollar of MAGI over $150,000 joint ($75,000 single). The retired couple in the first row would lose part of that deduction on top of the $6,920. The Roth conversion calculator runs these layers together for a specific set of numbers.

Sizing a December conversion: brackets and cliffs

Converting late lets you size with almost-final numbers. For 2026, the IRS's inflation-adjusted brackets put the top of the 24% bracket at $403,550 of taxable income for married couples filing jointly ($201,775 single), with 32% above that and 35% from $512,450 ($256,225 single).

Worked example. A married couple, both 66, reviews their numbers on December 4, 2026. With salary, a partnership K-1 estimate and dividends, they project taxable income of $310,000. The headroom to the top of the 24% bracket is $403,550 − $310,000 = $93,550. Converting $93,550 adds $22,452 of federal tax at 24%. Converting $150,000 instead would put $56,450 into the 32% bracket and add $40,516 of federal tax, an extra $18,064 for $56,450 more converted, or 32% on the increment. Whether that increment is worth it depends on the rate those dollars would otherwise face later, as RMDs or in an heir's hands, which is the question a conversion calculator is built to model.

The bracket is only the visible threshold. Conversion income is "included in income for all purposes," in the words of §1.408A-4, A-9, so it also raises the AGI and MAGI that drive other rules:

• Net investment income tax. Conversion income is not itself investment income, but it can push MAGI over the unindexed $200,000 single / $250,000 joint thresholds in IRC §1411, exposing dividends, interest and capital gains to the 3.8% tax.
• The SALT cap phase-down. The 2025 tax law raised the state and local tax deduction cap to $40,400 for 2026 but, under IRC §164(b)(7), reduces it by 30% of MAGI above $505,000 (joint or single), down to a floor of $10,000. For itemizers in that range, each converted dollar also removes 30 cents of deduction, so the effective federal rate on that slice is the bracket rate plus roughly a third of it again until the floor is reached.

A decision rule that holds up in practice: fill the bracket you are already in, stop short of the next IRMAA tier if you are 63 or older, and treat the NIIT and SALT thresholds as additional stop lines if your other income puts you near them.

IRMAA: the conversion's two-year echo

Medicare Part B and Part D premiums are set using MAGI from two years earlier, as the Social Security Administration explains. A conversion completed by December 31, 2026 therefore sets 2028 premiums, so anyone 63 or older in 2026 should treat IRMAA as part of the deadline decision. The 2028 thresholds will not be published until late 2027; the 2026 tiers below are a proxy, and because the thresholds are indexed, the 2028 brackets will probably sit somewhat higher.

Using the 2026 tiers published by CMS and the SSA's 2026 IRMAA tables for illustration: a married couple filing jointly with MAGI of exactly $410,000 sits at the top of the third surcharge tier, paying $324.60 per person per month in Part B surcharge and $60.40 in Part D surcharge. One more dollar puts them in the next tier, at $446.30 and $83.30. That is $144.60 a month per person, or about $3,470 a year for the couple, triggered by a single dollar of conversion. Because IRMAA is a cliff, the December precision that late-year conversions allow is worth the most here. Our IRMAA guide explains the tiers in full, and the IRMAA calculator shows where a given conversion lands.

The five-year clock rewards late-year conversions

Each conversion has its own five-year period for the 10% early-distribution penalty, and under Regulation §1.408A-6, A-5 that period begins on the first day of the tax year of the conversion. A conversion processed on December 15, 2026 is treated as starting its clock on January 1, 2026, the same as one done in January, and both clear on January 1, 2031. In effect, a December conversion gets almost a full year of seasoning for free, which removes one argument for converting early in the year.

Missing the deadline by a few days costs the opposite: a conversion that posts on January 4, 2027 starts its clock on January 1, 2027 and does not clear until 2032. For anyone already past 59½, the conversion clock no longer drives the penalty question; the full set of rules is in our Roth conversion 5-year rule guide.

Paying the tax: withholding versus estimates

A large December conversion creates a tax bill that the year's earlier estimated payments probably did not anticipate. The balance itself is due with the return on April 15, 2027, but the underpayment rules in IRC §6654 run through the year. There are two clean ways to stay inside them, both explained in IRS Publication 505:

• Pay a fourth-quarter estimate by January 15, 2027. If earlier payments already met a safe harbor (110% of the prior year's tax when prior-year AGI exceeds $150,000, under §6654(d)(1)(C)), there is generally no underpayment penalty even with a large April balance. If you rely on the current-year 90% test instead, the annualized income installment method on Form 2210 matches December income to the last installment rather than spreading it back over the year.
• Withhold from another IRA distribution. Under §6654(g), federal withholding is treated as paid in equal parts across the year unless you elect otherwise, so December withholding can cover a shortfall from earlier quarters. Withholding from the conversion itself shrinks what reaches the Roth, and under 59½ the withheld portion can carry the 10% additional tax. Paying from taxable assets keeps the full amount in the Roth.

Early in the year or late? A decision rule

With recharacterization gone, timing is a trade-off between growth and information. A January conversion buys eleven extra months of tax-free growth but is sized blind. A December conversion gives up those months for near-certain knowledge of your bracket, IRMAA position and asset values, and the five-year clock treats both dates the same.

A rule that holds up: volatile income (K-1s, bonuses, a business sale, large gains) argues for the bulk of the conversion in late November or early December, once the picture is settled. Predictable income, as in a gap year funded from savings, suits a conservative base conversion early with a December top-up. A sharp market drawdown moves more shares for the same tax whenever it arrives. Readers 60 and over weighing a multi-year schedule will find the age-specific trade-offs in our guide to converting an IRA to a Roth after 60.

Whatever the plan, treat December 31 as the latest possible date and mid-December as the working deadline.