How a Mega Backdoor Roth works
Normal Roth IRA contributions are capped at $7,500/year (2026), and income limits phase out eligibility entirely. The mega backdoor Roth gets around both restrictions using your 401(k) plan.
The Two Key Insights
401(k) plans allow after-tax contributions beyond the standard pre-tax/Roth contribution limit. The total 401(k) limit (employee + employer + after-tax) is $70,000 in 2025.
After-tax 401(k) money can be converted to Roth, either inside the plan or by rolling it to a Roth IRA.
Step-by-Step
Max out your regular 401(k) — contribute the $24,500 employee limit (pre-tax or Roth).
Make after-tax contributions — contribute additional after-tax dollars up to the $72,000 total plan limit (minus employer match and your regular contributions). This gap can be up to ~$40,000+ depending on your employer match.
Convert those after-tax dollars to Roth — via one of two routes:
In-plan Roth conversion — if your plan allows it, convert the after-tax balance to a Roth 401(k) inside the plan.
Roll over to a Roth IRA — if your plan allows in-service withdrawals, roll the after-tax funds directly to a Roth IRA.
You want to do this conversion quickly (ideally immediately, hence "backdoor") so the after-tax money hasn't earned much taxable growth yet. Only the gains — not the contributions — are taxable on conversion.
The Catch
Your plan must allow it — not all 401(k) plans permit after-tax contributions or in-service withdrawals/conversions. This is the biggest obstacle.
Pro-rata rule risk — if earnings accumulate before you convert, those gains are taxable.
ADP/ACP testing — at some companies, highly compensated employees may be restricted if lower-paid employees don't participate enough.
Who Should Consider It
It's most useful for high earners who are already maxing out their regular 401(k) and Roth IRA, have a plan that supports it, and want more tax-free growth for retirement.
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