Mega Backdoor Roth: What the Plan Must Allow, According to the Sources

You may have seen the phrase "mega backdoor Roth." It is not an official IRS name. This guide explains the pieces behind it using IRS and statute text. Some points depend on how several rules fit together, so we label them our interpretation and show the source. This page explains rules only. It is not advice for any person, and a qualified tax professional should review your own plan and facts.

What do people mean by a "mega backdoor Roth"?

The phrase usually describes a chain of steps:

1. A worker puts after-tax money into a 401(k) plan. "After-tax" means you pay income tax on the money before it goes in, and you do not deduct it.
2. The after-tax money, and sometimes its earnings, is later moved into Roth money. That move is either a rollover to a Roth IRA or a rollover inside the plan to a designated Roth account (an "in-plan Roth rollover").

The word "mega" refers to the size of the room for after-tax money. It is much larger than the IRA limit, as the next section shows. Our backdoor Roth IRA and pro-rata rule article covers the smaller, IRA-based version.

What are the 2026 limits behind it?

Two different limits matter, and people often mix them up.

The IRS page says the annual additions paid to a participant's account cannot exceed the lesser of those two amounts. It lists four things that count: elective deferrals (but not catch-up contributions), employer matching contributions, employer nonelective contributions, and allocations of forfeitures. It does not mention after-tax contributions.

The tax code does. Section 415(c)(2) says an "annual addition" is the sum of employer contributions, employee contributions and forfeitures (26 U.S.C. 415). The Treasury regulation says the term "includes mandatory employee contributions" as well as voluntary ones (26 CFR 1.415(c)-1).

Our interpretation: after-tax contributions count toward the total limit, and that total limit is what gives the "mega" room. The room is whatever is left after the other items on the list.

A simple illustration

This is our own arithmetic, not an IRS example. It uses a worker under 50 with enough pay, and it assumes nothing else counts toward the total.

Your own plan may have other limits, and we did not review other tests that can apply to plans. Check your plan documents.

What must the plan allow?

This is the heart of the question. A 401(k) plan does not simply offer everything the tax law permits.

• After-tax contributions. The IRS qualification page and the contribution limits page we opened do not address them. We did not find an IRS statement that plans must offer them. Our interpretation: because no source we opened requires it, assume your plan may not offer it. Ask your plan administrator.
• In-plan Roth rollovers. The IRS says "A plan isn't required to offer designated Roth accounts or in-plan Roth rollovers," and that a plan may stop offering them (IRS). The designated Roth FAQ describes in-plan Roth rollovers as something plans "may offer" (IRS FAQ).
• Moving money out while you still work. The IRS says distributions generally cannot be made until a "distributable event" occurs, and lists reaching age 59½ or financial hardship among them (IRS). The IRS also says that, beginning in 2013, a plan may allow in-plan Roth rollovers of amounts that are not otherwise distributable (IRS). We did not find a source stating when a plan may let you take after-tax money to a Roth IRA while still employed. The plan's rules control that.

How are the after-tax dollars moved?

The IRS after-tax rollover page says that "after-tax contributions can be rolled over to a Roth IRA without also including earnings." Earnings on after-tax contributions count as pretax amounts. You also cannot take only the after-tax portion: "Any partial distribution from the plan must include some of the pretax amounts." Distributions sent to several destinations at the same time are treated as a single distribution, which lets pretax money go to one place and after-tax money to another (IRS). Our after-tax 401(k) rollover guide walks through the notice's examples.

What about taxes?

Two points, each tied to a source:

• For an in-plan Roth rollover, the IRS FAQ says you generally include the taxable amount (it defines this as fair market value minus your basis in the distribution) in gross income for the tax year you receive it. Our interpretation: the pretax part is taxable and the after-tax basis is not (IRS FAQ).
• The same FAQ says "you may not recharacterize an in-plan Roth rollover." Our interpretation: the step cannot be undone, so timing and the amount of earnings matter.

We did not open sources on state tax, the Roth five-year rules, or reporting forms for these rollovers, so we make no statement about them.

What are the common mistakes?

• Assuming the plan offers the feature because the tax law allows it. The plan document decides.
• Mixing up the $24,500 deferral limit and the $72,000 total limit.
• Forgetting that employer contributions use up part of the total limit.
• Expecting to roll over only the after-tax dollars and leave the rest. The IRS says partial distributions include some pretax amounts.
• Treating an in-plan Roth rollover as reversible. The IRS says it cannot be recharacterized.

Related questions

Is this the same as a backdoor Roth IRA? No. The backdoor Roth IRA uses IRA contributions. See our backdoor Roth article and the IRA vs 401(k) comparison.

Do Roth and traditional accounts differ in other ways? Yes. See traditional vs Roth IRA.

Who can interpret my plan? Your plan administrator for plan features and a tax professional for your own situation.

Where gold and silver IRAs fit - and where they do not

A mega backdoor Roth is about how money gets into Roth accounts. It does not decide what the money is invested in. If the end result is a Roth IRA, some savers choose to hold part of it in gold or silver. People who do so often point to diversification away from stocks and bonds, to the appeal of a physical asset, and to how metals have behaved in past inflationary periods. Those are arguments, not promises, and the sources cited on this page do not test them.

The costs and rules matter just as much. A precious-metals IRA can carry setup, annual, storage and dealer-spread costs, and metal prices can fall as well as rise. Our guides explain the IRS rules on which metals an IRA may hold, with sources. Rolling money into a self-directed IRA has its own paperwork. See Roth Gold IRA, Gold IRA fees, Gold IRA risks and in-service rollovers. No source here suggests how much of anyone's savings, if any, belongs in metals. A tax professional or fee-only planner can help with that.

What we did not check: Notice 2014-54 itself (we relied on the IRS page that describes it), Notice 2013-74, plan nondiscrimination tests, state tax, and Roth five-year rules.