Does my 401(k) plan allow a mega backdoor Roth, and what do I need to check?

By Kaz · Published 6 October 2026 · How this site checks figures

Summary

Only if your plan document allows two things: after-tax employee contributions that aren't Roth, and a way to move that money into Roth status while you're still employed. That second step is either an in-plan Roth rollover or an in-service withdrawal of after-tax money, and a plan doesn't have to offer either. The room for it in 2026 is the $72,000 annual additions limit minus your own deferrals and everything your employer puts in; catch-up contributions don't count against it. "Mega backdoor Roth" is not an IRS term, so the plan's documents won't use it.

Four questions for the plan

The answers are in the summary plan description, or HR and the recordkeeper can confirm them in writing.

Question	Why it decides
Does the plan accept after-tax employee contributions, separate from Roth deferrals?	Without them there is nothing to convert. Roth 401(k) deferrals share the $24,500 deferral limit for 2026; after-tax contributions don't
Does it allow in-plan Roth rollovers, including of after-tax money?	The IRS says plans "are not mandated" to offer them
Does it allow in-service withdrawals of after-tax money?	That is the route to a Roth IRA instead of a Roth account inside the plan
How often can you convert or withdraw: per paycheck, quarterly, once a year?	Earnings build up between conversions, and earnings are taxed when converted

A fifth question matters if this employer paid you more than $160,000 in the prior year, the highly compensated employee threshold the IRS lists for both 2025 and 2026: whether after-tax contributions are capped or refunded after the plan's nondiscrimination testing.

How much room there is in 2026

Example: you're 45, defer $24,500 in 2026, and your employer adds $9,000 in matching. The IRS limit on annual additions to one account for 2026 is the lesser of 100% of compensation or $72,000.

$72,000 − $24,500 − $9,000 = $38,500 of possible after-tax contributions.

At 55 you could also make the $8,000 catch-up for 2026, and the room would still be $38,500, because the IRS says catch-up contributions are outside the $72,000. A larger employer contribution reduces the room dollar for dollar, so a profit-sharing contribution that arrives after year-end can shrink a figure you thought was fixed. Ask HR for the expected total before setting your after-tax percentage. The 2026 retirement account limits lists every limit in one place.

The two routes out

Getting after-tax 401(k) money into Roth status while employed

Does the plan accept after-tax (non-Roth) contributions?

No → No mega backdoor in this plan

Yes → Continue

Does it offer in-plan Roth rollovers of after-tax money?

Yes → The money becomes Roth inside the plan; earnings converted with it are taxable; it can't be reversed

No → Check in-service withdrawals

Does it allow in-service withdrawals of after-tax money?

Yes → Contributions can go to a Roth IRA and earnings to a traditional IRA in the same distribution

No → The money waits until you leave, and earnings on it grow as pretax money

Have you asked how often conversions or withdrawals are allowed?

Not yet → Ask before contributing; the answer sets how much earnings will be taxed

Yes → Set contributions around that schedule

A checklist of plan features, not a recommendation. Each answer comes from your plan's documents.

Source: IRS, Retirement topics: designated Roth account; Rollovers of after-tax contributions; Notice 2013-74

Inside the plan, the IRS says "any vested plan balance, including earnings, can be rolled over to a designated Roth account" if the plan allows it, and that "an in-plan Roth rollover cannot be reversed after the transfer is made." Notice 2013-74 lets plans convert money that isn't otherwise distributable, but only by direct rollover, and says no withholding applies to it, so any tax on converted earnings is paid with your return.

Out to a Roth IRA, the IRS's after-tax rollover rules apply: earnings on after-tax contributions are treated as pretax, and a single distribution can send the contributions to a Roth IRA and the earnings to a traditional IRA. Splitting after-tax and pretax 401(k) money walks through the IRS example. If that traditional IRA receives pretax earnings and you also do a regular backdoor Roth, the backdoor Roth and the pro-rata rule shows what those dollars do to the calculation.

Why higher earners sometimes get refunds

After-tax contributions are tested under the ACP test, which the IRS describes as covering "matching and after-tax contributions." When a plan fails, one correction the IRS describes is to distribute the excess to highly compensated employees. For those employees the after-tax money comes back as a refund rather than staying in the plan to be converted. HR can tell you whether the plan has refunded after-tax contributions after recent tests.

Between conversions, the after-tax money sits in whichever plan fund you picked. The fee calculator shows what a fund's yearly percentage takes from $38,500 over time.

Sources

Written by Kaz, an independent publisher.
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