While overseeing your company’s 401(k) plan, you may have encountered questions about “Mega Backdoor Roth” contributions. This strategy has gained attention as a way for participants to make Roth contributions beyond the standard deferral limits – up to the overall annual cap on total contributions. Mega Backdoor Roth involves contributing after-tax dollars to the 401(k) plan and then converting them to Roth.
First, your plan must permit both after-tax contributions and in-plan Roth conversions for this to be feasible. Even with these features in place, however, implementation can be administratively complex. Here are key hurdles and scenarios where it might succeed.
Navigating the ACP Test
After-tax contributions are subject to the Actual Contribution Percentage (ACP) test, which ensures that employer matches don’t disproportionately favor highly compensated employees (HCEs) over non-HCEs. If this test fails, excess after-tax amounts must be refunded rather than converted to Roth – a common issue since Mega Backdoor users are often HCEs.
Notably, safe harbor plans, which are typically exempt from ACP testing, will require the testing be completed if after-tax contributions are made. As such, if a business has any non-owner employees, even safe harbor plans plan will generally not pass the ACP test after accounting for after-tax contributions by HCEs and most, if not all, after-tax contributions will not be able to remain in the plan.
Recordkeeper/Investment Provider Limitations
Not all recordkeepers or investment platforms support Roth conversions of after-tax dollars. Some restrict conversions to amounts eligible for in-service distributions, which may not be available until participants reach age 59-½. Before adding Roth conversions to your plan, verify your provider’s capabilities to ensure smooth processing and avoid participant frustration.
Ideal Scenarios for Implementation
Mega Backdoor Roth is most effective in owner-only or HCE-exclusive plans, where the absence of non-HCEs eliminates ACP test risks. Participants remain bound by the Section 415 annual additions limit—$72,000 for 2026, which encompasses all contribution types (employee deferrals, employer matches, and after-tax amounts).
While the appeal of enhanced Roth contributions is understandable, Mega Backdoor Roth is really only viable in select plan designs and requires careful administrative oversight. We recommend consulting your Blue Ridge Plan Administration Consultant to evaluate your plan’s eligibility, potential testing implications, and how to integrate this feature effectively.
