The Mega Backdoor Roth: Are Your Clients Leaving Tax-Free Money on the Table?

Sharon Kreider, CPA

Most of your clients who are serious about retirement savings know the basics – max the 401(k), fund the Roth IRA if they’re eligible, maybe do a backdoor Roth conversion if income is too high. But there’s a third layer that a surprising number of clients overlook entirely—the Mega Backdoor Roth.

It’s not complicated once you understand it, but the window to use it is narrow, and not every plan allows it. And with a significant rule change hitting in 2026, there’s more reason than ever to be having this conversation with your higher-income clients now.

The Basic Math

In 2026, the elective deferral limit is $24,500. On top of that, employees age 50 and older can add a catch-up contribution of $8,000 – and those ages 60 through 63 get an even larger “super catch-up” of $11,250 under SECURE 2.0. But the total §415 limit – everything going into the plan from all sources – is $72,000. That gap between what your client defers and the §415 ceiling is the opportunity.

If the plan allows after-tax contributions, your client can fill that gap with after-tax dollars and then convert them to Roth through an in-plan conversion. Quick example:

A client under 50 defers $24,500 and gets a $15,000 employer match. They potentially have over $32,500 in after-tax contribution room.

Convert that to Roth promptly, and you’ve added a significant Roth balance in a single year, completely separate from and with no effect on any Roth IRA contributions. The “convert promptly” part matters. The longer after-tax dollars sit before conversion, the more pre-conversion earnings accumulate, and those are taxable on conversion. In the best case scenario, the plan has an automatic conversion feature. If it doesn’t, your client needs to be proactive – ideally converting the same day or within the same pay period.

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The Catch

Three things must be true for the Mega Backdoor strategy to work:

The plan must allow after-tax employee contributions.
It must allow in-plan Roth conversions or in-service distributions to a Roth IRA.
Your client needs to have the cash flow to fund the plan after maxing regular deferrals.

The last point eliminates a lot of people. This is really a strategy for clients who are already maxed out and asking, “what else can I do?”

If a client isn’t sure whether their plan allows it, they should pull the Summary Plan Description or call their HR.

A Word to Anyone Who Influences Plan Design

Your clients who are business owners, HR leaders, or benefits managers need to know that adding after-tax contributions and in-plan Roth conversions to a 401(k) costs the employer nothing but some administrative costs. There is no change to the match, no new employer obligation, or minimal administrative burden in most cases. It’s a pure employee benefit – and a valuable one for your higher earners.

But there’s a more urgent point in 2026: if a plan doesn’t currently offer a Roth option at all, that’s now a compliance problem, not just a missed opportunity. High earners in pre-tax-only plans lose their catch-up contributions entirely under the new rules. Under final regulations issued in 2025, plan amendments to add a Roth feature are due by December 31, 2026, but operational compliance is required right now. Any client with influence over their company’s plan document needs to be talking to their pension administrator immediately if Roth isn’t already available.

Bottom Line

The Mega Backdoor Roth won’t apply to every client, but for those who are already maxed out and have the income to go further, it can dramatically accelerate Roth accumulation in a way no other strategy matches. Layer in the new mandatory Roth catch-up rules for high earners, and 2026 is shaping up to be a pivotal year for Roth planning conversations. It’s worth adding to the checklist when you’re doing annual planning reviews – because if the plan allows it and your client doesn’t know about it, that’s just money left on the table.