What is a mega backdoor Roth?

By Nicolas StrautPublished August 19, 20267 min read

Key takeaways

The 2026 ceiling on everything that can go into your 401(k) is $72,000, and your own deferrals and your employer's money come out of that total first.¹
A mega backdoor Roth is a two-leg sequence, run inside a 401(k) rather than an IRA: after-tax contributions beyond the $24,500 deferral limit, then converted to Roth, either in-plan or rolled out to a Roth IRA.
Most 401(k) plans don't allow a mega backdoor Roth, since it requires both after-tax contributions and a conversion route that the plan document has to permit explicitly.

In this article

What is a mega backdoor Roth?
What is the 2026 mega backdoor Roth limit?
Does your 401(k) allow a mega backdoor Roth?
Can a nondiscrimination test undo your mega backdoor Roth contributions?
Should you convert your mega backdoor Roth in-plan or roll it out to a Roth IRA?
How to do a mega backdoor Roth in 3 steps
Frequently asked questions about the mega backdoor Roth

A mega backdoor Roth means making after-tax contributions to your 401(k) beyond the normal deferral limit, then converting them to Roth. In 2026 the total that can go into your 401(k) from every source is $72,000. Whatever's left after your own deferrals and your employer's money is your after-tax room.

What is a mega backdoor Roth?

A mega backdoor Roth is a two-leg sequence, run inside a 401(k) rather than an IRA: contribute after-tax dollars above the $24,500 deferral limit, then move them into Roth, either inside the plan or out to a Roth IRA. Neither leg has an income limit.

The name "mega" refers to the amount of money it moves. The regular backdoor Roth moves $7,500 a year. This version can move tens of thousands. Our backdoor Roth guide covers the IRA version in full.

	Backdoor Roth IRA	Mega backdoor Roth
Vehicle	Traditional IRA to Roth IRA	401(k) after-tax to Roth
2026 ceiling	$7,500 or $8,600	Up to $72,000 minus everything else
Income limit	None	None
Main obstacle	Your other IRA balances	Whether your plan allows it

The three kinds of 401(k) contribution

A mega backdoor Roth depends on three kinds of 401(k) contribution, which plan portals often mislabel:

Pre-tax deferrals: No tax now, taxed on withdrawal, and counts against the deferral limit.
Designated Roth deferrals: Taxed now, never taxed again, and also counts against the deferral limit.
After-tax non-Roth contributions: Taxed now, and the earnings are taxed on withdrawal unless converted. After-tax contributions are the type a mega backdoor Roth uses, and they're a separate plan feature from the other two.

If your plan portal only offers "pre-tax" and "Roth," you probably don't have after-tax contributions. Plan websites frequently mislabel one type as another, so confirm with your plan before you assume the feature exists.

What is the 2026 mega backdoor Roth limit?

There's no separate "mega backdoor" limit written anywhere. There's one overall limit on everything going into your 401(k), and after-tax contributions fill whatever's left of it.

Limit	2026
Total annual additions, §415(c)	$72,000
Your own elective deferrals, §402(g)	$24,500
Age 50+ catch-up, §414(v)	$8,000
Ages 60–63 super catch-up	$11,250, unchanged from 2025
Compensation limit, §401(a)(17)	$360,000

Start with the lesser of $72,000 or 100% of your compensation.⁴Subtract your own deferrals, your employer's match, any profit-sharing or non-elective contributions, and any forfeitures allocated to your account. What's left is your after-tax room, further capped by whatever percentage of pay your plan allows.

Two more details matter. The $72,000 figure is the lesser of that dollar amount or 100% of compensation. For anyone with modest pay, the 100% of compensation cap applies first. Forfeitures allocated to your account also count toward the total.

Situation	Deferrals	Employer money	After-tax room
No employer contribution	$24,500	$0	$47,500
50% match on 6% of $200,000	$24,500	$6,000	$41,500
Generous profit sharing	$24,500	$25,000	$22,500
Age 62, super catch-up	$24,500 + $11,250	$6,000	$41,500

Stacked bar of the 2026 401(k) limit of $72,000 for a $200,000 salary with a 50% match on 6% of pay: $24,500 of employee deferrals, $6,000 of employer match, and $41,500 of after-tax room for a mega backdoor Roth. — The second row of the table above as a bar: after-tax contributions fill whatever is left of the total limit.

Do catch-up contributions count toward the limit?

No. Catch-up contributions aren't annual additions and don't count against §415(c), under two separate regulations.³But a catch-up contribution has to be an elective deferral, pre-tax or designated Roth. An after-tax employee contribution can't be one.

Together, these two rules mean catch-up contributions neither reduce nor expand your after-tax room. Catch-up contributions raise only the total you can put into the plan. At 50 or older, that ceiling is effectively $80,000. At 60 to 63, it's $83,250. Your after-tax room is the same either way.

If you read "your limit is $80,000" and plan $55,500 of after-tax contributions accordingly, your plan's recordkeeper will correct you. Separately, if your prior-year Social Security wages from that employer exceeded $150,000, SECURE 2.0 requires your 2026 catch-up to be Roth. That rule governs catch-up deferrals, not after-tax contributions, so it doesn't change this math.

Does your 401(k) allow a mega backdoor Roth?

Most plans don't. A plan needs two separate features for a mega backdoor Roth:

The plan has to permit voluntary after-tax employee contributions. This is the rarer of the two.
The plan has to permit a conversion route: an in-plan Roth rollover, an in-service distribution of the after-tax subaccount, or both.

Look in your summary plan description under headings like "Employee After-Tax Contributions" and "In-Service Withdrawals." Both features need to be present. When you ask HR or your recordkeeper, three questions get you an unambiguous answer:

Does the plan permit voluntary after-tax employee contributions, separate from Roth deferrals?
Does it permit in-plan Roth rollovers, in-service distributions of the after-tax subaccount, or both?
Is there an automatic conversion feature, and how often does it run?

Most plans cap after-tax contributions at a percentage of pay, often well below what $72,000 would otherwise allow. Ask for the percentage, not just whether the feature exists.

A solo 401(k) can be written to permit after-tax contributions and in-plan conversions. With no employees, a solo 401(k) has no nondiscrimination test to fail.

Can a nondiscrimination test undo your mega backdoor Roth contributions?

Yes, if you're a highly compensated employee and the plan fails its actual contribution percentage test. The ACP test compares the rate at which highly compensated employees make after-tax and matched contributions with the rate for everyone else. If the gap is too wide, the plan fails and has to fix it.

Safe harbor status doesn't exempt after-tax contributions. A safe harbor plan offering employee after-tax contributions still has to pass the ACP test.³Safe harbor covers matching contributions only. If your prior-year compensation was above $160,000, this rule applies to you.

A failure means a corrective distribution of your after-tax contributions, plus whatever earnings they generated. That correction can land months into the following year, well after you've already converted the money. ACP test failures are common. Plans with automatic conversion features often see low participation from non-highly-compensated employees because the feature is hard to understand. Low participation widens the gap between the two groups, and that gap is what fails the test.

Should you convert your mega backdoor Roth in-plan or roll it out to a Roth IRA?

	In-plan Roth rollover	In-service rollout to a Roth IRA
Where it lands	Designated Roth account in your 401(k)	Your Roth IRA
Five-year clock	Plan-specific, doesn't aggregate with your Roth IRA	Inherits your existing Roth IRA clock
Investments	The plan's menu	Anything
Fees	Often institutional share classes	Retail pricing
Access to basis	No contribution-basis ordering access	Ordering rules make basis available first
Creditor protection	ERISA anti-alienation	State law and bankruptcy code
Splitting off earnings	Not available	Available under Notice 2014-54

The strongest argument for the rollout route is the five-year clock. If you've already held a Roth IRA for years, money rolled into it inherits that already-satisfied clock. Money converted in-plan starts a separate, plan-specific one instead. Some plans only offer one of the two routes. In that case, use the route your plan offers.

What happens to the earnings before you convert

After-tax money that sits in the plan before conversion can earn gains, and those earnings are pre-tax. When you convert, those earnings become taxable income for the year. How much in earnings builds up depends on your plan's conversion schedule: some convert daily and automatically, some batch quarterly, and some require you to call and ask.

IRS Notice 2014-54 offers a way to split the rollover.²Because disbursements scheduled at the same time count as a single distribution, you can direct your after-tax basis to a Roth IRA and the pre-tax earnings to a traditional IRA, tax-free, as long as you tell the plan administrator before the rollovers happen. This split only works on the rollout route.

The IRA pro-rata rule doesn't apply to your 401(k) after-tax subaccount. The aggregation rule only applies to individual retirement plans, and a defined contribution plan's employee contributions can be treated as a separate contract under a different code section.⁴The separate-contract treatment is optional, not automatic. The pro-rata rule still applies inside the after-tax subaccount, between your basis and its earnings.

How to do a mega backdoor Roth in 3 steps

Contribute the max to your elective deferrals. Then calculate your remaining §415(c) room using the employer contributions you received, not an estimate. The 401(k) calculator runs your plan's match formula against the §415(c) and compensation limits.
Elect after-tax contributions through your plan, up to the lower of that room and your plan's percentage-of-pay cap.
Convert as soon as the plan permits. Automatic conversion, where it's offered, is the best option, since it keeps the taxable earnings close to zero.

Expect a Form 1099-R for the conversion, with the gross amount in Box 1, the taxable amount in Box 2a, your after-tax basis in Box 5, and distribution Code G in Box 7a. The 2026 revision renumbered the old Box 7 to Box 7a; Code G itself didn't change.⁵

Frequently asked questions about the mega backdoor Roth

Does a mega backdoor Roth affect my regular Roth IRA contribution limit?

No, a mega backdoor Roth doesn't affect your regular Roth IRA contribution limit, because the two limits are entirely separate. Your 401(k) sits under the annual additions limit, and your IRA sits under its own, much smaller limit. A contribution to one doesn't reduce the other, so you can fund both a mega backdoor Roth and a regular backdoor Roth in the same year.

Can I do this if I earn too much for a Roth IRA?

Yes, you can do a mega backdoor Roth even if you earn too much for a Roth IRA, because income limits don't apply here at all. The Roth IRA MAGI phase-out only governs direct contributions to an IRA. Neither an after-tax 401(k) contribution nor a conversion has an income limit. This is why high earners use the mega backdoor Roth.

Can I withdraw the converted money early?

Whether you can withdraw the converted money early depends on which route you used. Money rolled to a Roth IRA is generally accessible under the ordering rules, which make basis available first. Money converted in-plan to a designated Roth 401(k) doesn't have that same basis-first access, because that money is still governed by the plan's own distribution rules.

Does converting after-tax 401(k) money start a new five-year clock?

Only partly: converting after-tax 401(k) money starts a new five-year clock just for the taxable portion of that conversion. The recapture clock counts just the portion of a conversion includible in gross income, and your after-tax basis was never includible in the first place. If you roll the money into a Roth IRA you've already held for years, the rolled-over money inherits that account's already-satisfied qualified-distribution clock.

What are my options if my plan doesn’t allow this?

If your plan doesn't allow a mega backdoor Roth because the plan is missing one of the two required features, the realistic alternatives are a regular backdoor Roth, a health savings account if you have a qualifying plan, or a plain taxable brokerage account. You can also ask your plan sponsor whether they'd consider adding the missing feature.

Sources

https://www.irs.gov/newsroom/401k-limit-increases-to-24500-for-2026-ira-limit-increases-to-7500
https://www.irs.gov/pub/irs-drop/n-14-54.pdf
https://www.ecfr.gov/current/title-26
https://www.law.cornell.edu/uscode/text/26/415
https://www.irs.gov/instructions/i1099r

Whether this strategy is available to you depends entirely on your employer’s plan document, contributions can be returned if the plan fails nondiscrimination testing, and 2026 figures come from IRS Notice 2025-67. Tweed provides educational estimates, not financial advice. Confirm your specific situation with a qualified tax professional.

Nicolas Straut

Personal finance writer, former Forbes contributor and This Week in Fintech writer. He isn't a financial advisor or a CPA.

nicstraut.com