In-Plan Roth Conversion: Convert Pre-Tax 401(k) to Roth Without Leaving Your Plan

Most people assume Roth conversion requires leaving their job, rolling to an IRA, and converting from there. Not true. If your plan document permits it, you can convert pre-tax 401(k) balance directly to a designated Roth account inside the same plan — no distribution, no 60-day window, no rollover. This is called an in-plan Roth conversion (or in-plan Roth rollover). It's one of the least-discussed strategies in retirement planning, and starting in 2026 it's become more relevant than ever because of a mandatory Roth rule that quietly took effect for high earners.

How an in-plan Roth conversion works

Under IRC § 402A(c)(4),¹ a plan that offers a designated Roth account may allow participants to convert (roll over, in IRS terminology) some or all of their vested pre-tax balance into that Roth account. The mechanics:

1. You request the conversion. Contact your plan administrator or log into your plan portal and elect an in-plan Roth rollover. You specify the dollar amount (partial conversions are allowed if the plan permits).
2. The plan moves the money. The pre-tax balance is transferred to the Roth sleeve of your 401(k) account. No check is written to you, no 20% withholding, no 60-day clock.
3. You owe income tax. The converted amount is ordinary income in the tax year you do it — just as if you had converted to a Roth IRA. The plan does not withhold this tax; you pay it separately (estimated taxes or withholding from wages).
4. Future growth is Roth. Earnings on the converted balance compound tax-free and come out tax-free after the 5-year qualified distribution period is met.

No income limits. Unlike Roth IRA direct contributions (which phase out above $150,000 single / $236,000 MFJ in 2026), in-plan Roth conversions have no income ceiling. A participant earning $1 million can convert as much as their plan allows.

Irrevocable. The Tax Cuts and Jobs Act of 2017 eliminated Roth recharacterization for conversions. Once you convert, you cannot undo it. Plan accordingly — if you convert and the market drops 30% the same year, you cannot unwind the conversion to avoid paying tax on a higher value.

What you can convert

Two categories of balances can be converted, with slightly different rules:

The 5-year recapture rule (not the same as the Roth IRA 5-year rule)

This is the most misunderstood aspect of in-plan Roth conversions. There are actually two different 5-year rules involved:

Rule 1: The recapture rule (anti-abuse)

If you are under age 59½ and you take a distribution from your in-plan Roth conversion within 5 taxable years of when you made that conversion, the distributed converted amount is subject to the 10% early distribution penalty — even though you already paid income tax on it at conversion. The 5-year period starts January 1 of the year you did the conversion.

Example: You convert $150,000 in April 2026. The 5-year recapture window runs through December 31, 2030. If you separate from service at age 54 in 2027 and take a distribution of that converted balance, you'd owe a 10% penalty ($15,000) on top of... nothing else, because you already paid income tax in 2026. The penalty is the only risk, but it's real. At 59½ or after 5 years (whichever comes first), the recapture risk is gone.

Rule 2: The 5-year qualified distribution rule

To receive tax-free qualified distributions from a Roth 401(k), two tests must both be satisfied: (1) you're age 59½ or older (or disabled or deceased), and (2) the Roth account has been open for at least 5 taxable years. The 5-year period for the plan's designated Roth account starts January 1 of the first year you made a Roth contribution or in-plan conversion to that plan.

This is a single clock per plan (not per conversion). If you made a Roth contribution to the same plan in 2021, the 5-year qualified distribution clock has already been running since January 1, 2021. An in-plan conversion in 2026 doesn't restart it.

2026 change: Mandatory Roth catch-up contributions for high earners

Starting January 1, 2026, SECURE 2.0 § 603 takes effect.² If you earned $150,000 or more in FICA wages from your employer in 2025,³ every catch-up contribution you make in 2026 must be designated Roth — you can no longer make catch-up contributions on a pre-tax basis.

The 2026 limits affected by this rule:

The mandatory Roth catch-up rule doesn't force you to convert existing pre-tax balances — only new catch-up contributions going forward. But for many high earners it introduces a Roth component to their 401(k) for the first time, making an in-plan conversion of the existing pre-tax balance a natural follow-on consideration.

In-plan Roth conversion vs. rolling to a Roth IRA

When you're still employed, rolling to a Roth IRA isn't generally available (you need an in-service withdrawal, which most plans only allow at 59½+). But even after leaving a job or reaching 59½, in-plan conversion and Roth IRA rollover are genuinely different choices:

2026 Tax Cost Calculator

When an in-plan conversion makes sense

You're still employed and under 59½

This is the clearest use case. Rolling to a Roth IRA isn't an option (you can't take an in-service distribution before 59½ in most plans). If your plan supports in-plan conversions, this may be your only way to get money into a Roth account now, letting tax-free compounding begin earlier.

You want to preserve the Rule of 55

If you're in your early-to-mid 50s and considering retiring or changing jobs before 59½, the Rule of 55 gives you penalty-free access to your 401(k) after leaving at age 55+. Rolling to a Roth IRA forfeits that permanently. An in-plan conversion keeps the money in the plan, so converted Roth balances distribute penalty-free under Rule of 55 if you meet the age requirement.

You're a high-income earner in a lower-than-normal income year

In-plan conversion tax cost is identical to Roth IRA conversion cost — it's ordinary income either way. But a sabbatical, parental leave, medical leave, or business transition year where your W-2 income is temporarily depressed creates a window to convert at a lower marginal rate. A 22% conversion beats the 32% you'd pay in a normal year. If your plan allows partial in-plan conversions, you can fill a bracket each year without overspending on tax.

2026 mandatory catch-up, high earners

If SECURE 2.0 § 603 forces your catch-up contributions into Roth in 2026, you now have a Roth sleeve inside your 401(k) for the first time. That makes it worth considering whether to also convert part of your pre-tax balance — especially if your current marginal rate is lower than your projected retirement rate, or if you want to reduce future RMDs from pre-tax accounts.

When to roll to a Roth IRA instead

In-plan conversion is not always better. You might prefer rolling to a Roth IRA if:

• Your plan's fund menu is poor and you want access to low-cost index funds or individual securities not available in the plan.
• You've already left the job and there's no benefit to keeping the money in the former employer's plan.
• Your Roth IRA 5-year clock isn't started yet and starting it now (by opening a Roth IRA with a small conversion) gives you qualified-distribution eligibility years earlier than waiting for an in-plan conversion to start the Roth 401(k) clock.
• You're building a Roth conversion ladder for early retirement — that strategy requires money to be in a Roth IRA, not a Roth 401(k). See the Roth conversion ladder guide for details.

Real scenarios

Scenario A: High earner, age 52, 2026 mandatory catch-up triggers Roth strategy

Chen earns $230,000 (single) at a large tech company. His 2025 FICA wages exceeded $150,000, so in 2026 his $8,000 catch-up contribution must be Roth. His 401(k) now has a Roth sleeve for the first time. His current marginal rate is 32% (taxable income ~$214K, which is in the 32% bracket for single filers). He's projecting a 35% rate in retirement: his $1.8M pre-tax balance, growing at 4% annually, will generate RMDs of roughly $175,000–$200,000/year starting at age 75 — pushing his taxable income well into the 35% bracket even in today's terms.

He uses the calculator above to find exactly how much he can convert and stay within the 32% bracket (the 32% bracket top is $256,225 taxable for single; he has about $42,000 of room remaining). He converts $40,000, paying $12,800 in federal tax at a flat 32% effective rate. His rationale: every dollar converted at 32% avoids a 35% future rate. The $40,000 converted today may be worth $90,000+ at retirement — avoiding $31,500 in tax at 35% while the deferral cost is only $12,800 now. The money stays in the plan, preserving ERISA creditor protection and loan access.

Scenario B: Age 56, retiring in two years, pre-retirement bracket filling

Patricia is 56 with $900,000 in her 401(k) — all pre-tax. She plans to retire at 58. Her current salary pushes her into the 24% bracket. She expects RMDs starting at 75 on a $2M+ balance to hit the 35% bracket.

Her plan permits in-plan conversions of non-distributable balances. She converts $60,000 in 2026 and plans to convert a similar amount in 2027, filling the top of the 24% bracket each year. By retirement she'll have converted $120,000+ to Roth at 24% — reducing her projected RMD tax burden by an estimated $22,000/year and lowering her overall lifetime tax cost. She preserves the Rule of 55 the entire time because the money stays in the plan.

Scenario C: Age 43, medical leave, one-time low-income window

James is on extended medical leave from his $180,000/year job. His 2026 W-2 income will be approximately $42,000 (partial year plus short-term disability payments). He has $320,000 in pre-tax 401(k) contributions accumulated over 15 years and a plan that allows in-plan Roth conversions while still employed.

His taxable income after the $16,100 standard deduction is $25,900. He converts $45,000 — his taxable income after conversion is $70,900, spanning the 12% and 22% brackets. His federal tax on the conversion is approximately $7,450 (about 17% effective on the converted amount). In a normal year at his $180,000 salary, the same $45,000 conversion would cost roughly $11,400 — an effective rate of 25%. He's saving $3,950 in federal tax by converting this year instead of any normal year. He won't have another year this low until retirement. The converted balance compounds tax-free for 20+ years, inside the plan, with ERISA creditor protection intact.