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Mega Backdoor Roth Explained
An employee maxing a 401(k) at $24,500 still has room to move up to roughly $46,000 more into Roth in 2026 through the mega backdoor — if, and only if, the employer plan allows after-tax contributions plus in-plan conversion or in-service withdrawal. Fewer than one plan in five offers both features, but for those who qualify it is the largest legal Roth pipeline in the tax code.
Why the Room Exists
The famous $24,500 limit covers employee elective deferrals. A separate overall limit — $72,000 for 2026, excluding catch-ups — covers everything combined: your deferrals, the employer match, profit sharing, and standalone after-tax contributions. A worker with a 5% match on $200,000 of salary fills $10,000 of match, $24,500 of deferrals, and still has about $37,500 of combined room. After-tax contributions fill that leftover space, then convert immediately to Roth before any growth becomes taxable.
The Three-Step Mechanics
- Step 1. Confirm the plan document allows after-tax contributions and either in-plan Roth conversion or in-service distributions. HR or the summary plan description has the answer in writing.
- Step 2. Contribute after-tax dollars up to the remaining combined room, watching the anti-discrimination test boundaries where they apply.
- Step 3. Convert each contribution to Roth quickly — ideally automatically through payroll — so earnings before conversion, which would be taxable, stay near zero.
Who Should and Should Not
Best fit: high earners who have maxed every other account, expect to stay enrolled long enough for conversions to compound, and can fund living costs outside payroll savings. Wrong fit: anyone carrying expensive debt, lacking a six-month emergency fund, or planning to leave the job within months, since some plans restrict in-service access. Note the interaction with the regular backdoor Roth: large pre-tax IRA balances trigger pro-rata problems, but in-plan 401(k) conversions bypass that issue entirely, which is a quiet advantage of the mega route.
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