401(k) to Roth IRA Rollover: Tax Rules, When to Convert, and How to Split

Most people know you can roll a 401(k) to a traditional IRA without owing any tax. Fewer know you can roll it directly to a Roth IRA instead — in a single transaction, skipping the traditional IRA step entirely. The catch: the pre-tax portion of your 401(k) becomes ordinary income in the year you convert. For a $500,000 balance, that's a six-figure tax bill landing in April. So the question isn't just "can I?" — it's "should I, how much, and how do I minimize the damage if so?"

The mechanics: how a direct 401(k)-to-Roth rollover works

A direct 401(k)-to-Roth IRA rollover involves a trustee-to-trustee transfer. The 401(k) plan sends funds directly to the Roth IRA custodian — you never touch the money. Because it's a direct transfer, mandatory 20% withholding does not apply.¹

Step-by-step mechanics:

1. Open a Roth IRA (or have an existing one) at your chosen custodian — Fidelity, Vanguard, Schwab, or another.
2. Contact your 401(k) plan and request a direct rollover to your Roth IRA. Specifically request a "direct rollover to a Roth IRA." Give the plan the receiving account details (institution name, account number, routing info).
3. The plan issues a check payable to the Roth IRA custodian for your benefit (e.g., "Fidelity Investments FBO [Your Name] Roth IRA"). This is not payable to you — it's a direct transfer.
4. Deposit the check at your Roth IRA custodian within 60 days if it's issued to you as FBO — or it arrives directly at the custodian.
5. Tax reporting: Your 401(k) plan issues a Form 1099-R with Box 7 code G (direct rollover). You report the taxable amount on Form 1040 as ordinary income, and also on Form 8606 Part II to document the Roth conversion basis.

Tax treatment: what becomes taxable and what doesn't

A traditional 401(k) holds two categories of money:

• Pre-tax contributions and all earnings — these were never taxed. Rolling them to a Roth IRA triggers ordinary income tax in the year of rollover.
• After-tax (non-Roth) contributions — these were already taxed. Rolling them to a Roth IRA is tax-free. Under IRS Notice 2014-54, you can direct after-tax amounts to a Roth IRA and pre-tax amounts to a traditional IRA simultaneously — a "split rollover."² See the after-tax 401(k) split rollover guide for detail.

There is no 10% early withdrawal penalty on the conversion itself — even if you're under 59½.³ The penalty can apply later, though, if you withdraw the converted amount before it has seasoned for 5 years and you're still under 59½ (see the 5-year rules section below).

Direct-to-Roth vs. two-step: which is better?

The two alternatives are not always equivalent. Here's how they compare:

If tax rates are constant, both approaches produce identical after-tax outcomes. The math is symmetric: paying 22% now on $100K versus deferring and paying 22% on a larger balance later produces the same Roth value, adjusted for time value of the tax payment.

The two-step wins when:

• Your balance is large relative to your bracket capacity. Rolling $800K directly to Roth in one year would slam into the 32% or 35% bracket — burning a lot of conversion at a higher rate than you'd face if you spread it over 8–10 years at 22%.
• Your income varies year-to-year. If you expect lower-income years ahead (part-time work, gap year, early retirement transition), two-step lets you convert more in those low-income years.
• You need flexibility around IRMAA. If you or your spouse is on Medicare, a large one-year conversion can trigger surcharges that take two years to fall off. Two-step lets you manage around the $109,000/$218,000 threshold annually.⁴

Direct-to-Roth beats two-step when:

• The amount to convert is small (filling just your current bracket). A partial direct-to-Roth of the 12% bracket headroom — say $40,000 to a two-income couple — is efficient and avoids maintaining a traditional IRA pool afterward.
• You're in an unusually low income year at separation (partial-year wages, transition year). You'd convert at the same low rate whether direct or two-step — but going direct gets the money into Roth sooner, with no intermediary traditional IRA account to manage.
• You're trying to clear the traditional IRA pool for future backdoor Roth contributions. If you plan annual backdoor Roth IRA contributions ($7,500 for under 50, $8,600 for age 50+ in 2026), having a traditional IRA balance triggers the pro-rata rule. Rolling to Roth eliminates the pool problem in one step.⁵

2026 tax brackets — what your conversion will cost

The converted amount stacks on top of your other taxable income for the year. If you have $60,000 of other taxable income (MFJ, after standard deduction) and convert $80,000, the first $40,800 of conversion fills the 12% bracket and the remaining $39,200 hits the 22% bracket.

2026 brackets per IRS Rev. Proc. 2025-32. Standard deduction: $16,100 single / $32,200 MFJ. These are taxable income thresholds — income after subtracting your deductions.

The 5-year rules for converted Roth funds

Two different 5-year clocks apply to a Roth IRA funded by conversion. They are independent and often confused.

Clock 1 — Tax-free earnings: Roth IRA earnings are only tax-free on withdrawal if (a) you're 59½ or older AND (b) at least 5 years have passed since the first tax year you contributed to any Roth IRA. If you've never had a Roth IRA before, rolling 401(k) funds into a new Roth IRA starts this clock. If you opened a Roth IRA in 2019, even for $1, your clock already ran from 2019 and likely expired. Clock 1 is a single clock shared across all your Roth IRAs.⁶

Clock 2 — Penalty-free access to converted principal (under 59½ only): Each Roth conversion gets its own 5-year seasoning period for penalty purposes. If you're under 59½ and withdraw the converted amount within 5 years of the conversion, you owe the 10% early withdrawal penalty on the withdrawn amount — even though you already paid income tax when you converted. Once you're 59½, this clock no longer matters (the penalty exception for age 59½ overrides it).⁶

The withholding trap: always pay the tax from outside funds

When you convert $300,000 from your 401(k) to a Roth IRA, you'll owe federal income tax on the taxable amount. You have two ways to cover that bill:

1. Pay from outside the rollover (savings, taxable account, checking account). The entire $300,000 goes into your Roth IRA and compounds tax-free from day one. This is the right approach.
2. Withhold from the rollover itself. If you instruct the plan to withhold, say, 25% for taxes, only $225,000 actually reaches your Roth IRA. The $75,000 withheld is treated as a distribution — and if you're under 59½, you may also owe the 10% early withdrawal penalty on it.

The withholding approach is almost always worse. You reduce the Roth IRA balance by the withheld amount and potentially add a penalty. Pay the tax bill from other funds. If you don't have other funds available to cover a large conversion tax bill, that's a signal that converting a smaller amount — or doing the two-step over several years — makes more sense than a large direct-to-Roth rollover.

Partial direct-to-Roth: the optimal middle path

You don't have to choose "all to Roth" or "all to Traditional IRA." A split rollover lets you direct part of your 401(k) to a Roth IRA and part to a traditional IRA.

Example: You leave a job with $600,000 in a 401(k). You're married filing jointly, your other taxable income this year is $45,000 (partial-year wages), and the 12% bracket tops out at $100,800. That means you have $55,800 of 12% headroom. You roll $55,800 directly to a Roth IRA — paying about $6,696 in federal tax — and roll the remaining $544,200 to a traditional IRA. Next year, you evaluate whether to do more Roth conversions at a rate that still makes sense. You've permanently moved $55,800 into Roth at 12%, with no rush to convert the remaining balance at a worse rate.

This approach combines the immediate bracket efficiency of direct-to-Roth with the year-by-year flexibility of the two-step. It's how most advisors structure large rollover decisions.

Interactive tax-cost calculator

Estimate your federal tax cost for rolling your 401(k) directly to a Roth IRA. Enter your other income for the year (wages, pension, Social Security — before subtracting your standard deduction), the amount you're considering converting, and your filing status.

Who should go direct-to-Roth at the rollover moment

Strong candidates for full or partial direct-to-Roth

• Job-changers in a low-income year. Leaving a job mid-year often means below-normal wages. If your partial-year income is $50,000 and your marginal rate is 12%, converting a portion of the 401(k) at 12% is compelling — especially if you expect to be in the 22% bracket in retirement once Social Security, RMDs, and other income layer in.
• Small balances. If your 401(k) is $80,000 or less, the tax bill on a full direct-to-Roth conversion may be manageable in a single year, particularly if you have savings to cover it. You end up with a clean Roth IRA and no traditional IRA maintenance.
• Pro-rata rule relief. If you make backdoor Roth IRA contributions, having any traditional IRA balance triggers the pro-rata rule. Rolling your 401(k) directly to a Roth — rather than to a traditional IRA — keeps your traditional IRA pool empty and preserves backdoor Roth eligibility.
• Estate planning goals. Roth IRAs have no RMDs during the owner's lifetime, meaning the account can grow for decades without forced distributions. For people who don't need the money and want to pass it to heirs, Roth growth is estate-tax-free up to the federal exemption (permanently $15M under OBBBA) and income-tax-free to beneficiaries.

When to avoid direct-to-Roth (or convert only partially)

• Large balance, high current income. If your 401(k) is $700,000 and you're already in the 24% bracket from other income, converting the full balance pushes hundreds of thousands of dollars into the 32% and 35% brackets — permanently. The break-even versus a two-step approach is unfavorable unless you're very confident rates will be much higher later.
• No outside funds to pay the tax. If you'd need to withhold from the conversion to cover the tax, the math shifts materially against going direct-to-Roth. The withheld amount doesn't compound in Roth, and you may face a penalty on it if under 59½.
• Medicare-age taxpayers near the IRMAA threshold. A large one-year conversion that crosses the $109,000/$218,000 IRMAA threshold can trigger hundreds of dollars per month in Medicare surcharges — and those surcharges hit two years after the high-income year. The IRMAA "cliff" makes partial conversions that stay below the threshold far more efficient.
• You need the money in the next 5 years (under 59½). Converting creates a 5-year seasoning period on the converted principal for the 10% penalty. If you're 56 and might need $50,000 from the account at age 58, converting to Roth doesn't help — you'd owe penalty on the conversion principal withdrawn within 5 years. A traditional IRA or SEPP distribution might be more efficient.

Worked example: partial direct-to-Roth at job separation

Sarah, 51, leaves her employer in March 2026. Her income for the year is $62,000 (partial-year wages). She has $420,000 in her 401(k), all pre-tax. She's married filing jointly with her spouse who is not working.

Situation analysis:

• Other taxable income: $62,000 – $32,200 standard deduction = $29,800 taxable income
• 12% bracket top for MFJ: $100,800
• Headroom at 12%: $100,800 – $29,800 = $71,000 of conversion at 12%
• 22% bracket covers: $100,800 – $211,400
• IRMAA threshold: $218,000 MFJ. MAGI = $62,000 + conversion. To stay under IRMAA: max conversion = $156,000 (but she's not on Medicare, so this doesn't bind yet)

Decision: Sarah converts $71,000 directly to a Roth IRA (filling the 12% bracket). Tax cost: approximately $8,520 (12% × $71,000), paid from savings. She rolls the remaining $349,000 to a traditional IRA. Next year, she evaluates whether her income is low enough to do more conversions at 12% or 22%.

Result: $71,000 lands in Roth at 12% federal. Assuming 7% growth over 20 years, that $71,000 grows to approximately $274,000 — entirely tax-free. If she'd done nothing and left it in the traditional IRA, that same $274,000 would be fully taxable at withdrawal, likely at 22–24% when stacked with Social Security and other RMDs. The direct-to-Roth decision on just the bracket-filling amount is worth approximately $60,000 in lifetime tax savings in this scenario.

When an advisor earns their fee on this decision

The direct-to-Roth decision looks simple on the surface — pay taxes now, avoid them later — but it interacts with several other planning layers that change the answer:

• Social Security optimization. If you're delaying Social Security to age 70, that creates a "conversion window" of low-income years where Roth conversions are cheapest. A direct-to-Roth at job separation might be the first step in a multi-year conversion plan that needs to be sized around both the window and IRMAA.
• Roth conversion vs. Roth IRA contribution vs. after-tax 401(k) split rollover. If your 401(k) has after-tax basis, some dollars can move to Roth tax-free under IRS Notice 2014-54. An advisor identifies which part of the rollover to target and in what order.
• State tax. Some states exempt retirement income from tax; others tax Roth conversions the same as ordinary income. The federal 12% bracket might actually be 20%+ effective when state tax is included — changing the calculus on whether to convert now or later.
• The pro-rata interaction with future backdoor Roth contributions. If you plan backdoor Roth contributions going forward, the decision between direct-to-Roth and traditional IRA rollover has permanent implications. One wrong step creates a taxable pool that takes years to clear.