The Mega Backdoor Roth: How Some 401(k)s Let You Stash $70,000+ a Year Into Tax-Free Retirement Money

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If you have a 401(k) at work, there’s a chance you’re sitting on a tax-free retirement loophole worth tens of thousands of dollars a year and don’t know it. It’s called the mega backdoor Roth, and it lets the right savers funnel up to $72,000 a year into Roth retirement money. That’s the full plan maximum, far above the standard $7,500 IRA cap or $24,500 employee deferral.

The Reveal: Your 401(k) Has a Second Bucket

Most people know the standard 2026 employee deferral cap: $24,500 if you’re under 50. What almost nobody uses is the much bigger ceiling that governs all money flowing into your 401(k), including employer match and after-tax employee contributions. That total cap is $72,000 in 2026. The mega backdoor Roth fills the gap between your regular deferral plus match and that $72,000 ceiling with after-tax dollars, then converts those dollars to a Roth account. The growth is tax-free for life.

The Proof

The overall $72,000 limit lives in Internal Revenue Code §415(c), the section that caps annual additions to a defined contribution plan. The conversion mechanics rest on IRC §402A(c)(4) (in-plan Roth rollovers) and IRS Notice 2014-54, which lets you peel after-tax contributions off and roll them straight to a Roth IRA without dragging pretax money along. This is written directly into the tax code.

Who It’s For, Who It’s Not

You qualify only if your specific 401(k) plan document allows two things: (1) after-tax contributions (a separate bucket from pretax and Roth), and (2) in-service withdrawals or in-plan Roth conversions of those after-tax dollars. Big tech employers and large financial firms commonly allow both. Most small-employer plans do not. Call your plan administrator and ask, by name, “Does the plan allow voluntary after-tax contributions and in-service Roth conversions?” If either answer is no, you’re out, full stop. There is no income limit on this strategy, which is what makes it so powerful for high earners locked out of a regular Roth IRA.

How to Use It in 2026

1. Max your regular employee deferral first: $24,500 if you’re under 50, or $32,500 with the age 50+ catch-up. Workers aged 60 to 63 get a super catch-up bringing the total to $35,750.
2. Add up what your employer contributes (match plus profit-sharing). That counts toward the $72,000.
3. Subtract those two numbers from $72,000. What’s left is your after-tax contribution headroom.
4. Elect after-tax contributions in your payroll portal up to that headroom.
5. Convert them immediately. Either use an automatic in-plan Roth conversion (set it and forget it) or request an in-service rollover of after-tax dollars to a Roth IRA. Speed matters: the longer you wait, the more pretax earnings accumulate on the after-tax money, and those earnings get taxed at conversion.

One note for high earners: under SECURE 2.0, employees 50 and older who earned more than $150,000 in 2025 must already route their regular catch-up contributions into a Roth 401(k) starting this year. That doesn’t block the mega backdoor; it just changes the tax treatment of your normal catch-up.

The Catch

Three traps. First, plenty of plans cap after-tax contributions well below the §415(c) ceiling, or skip them entirely, so your real headroom may be smaller than the math suggests. Second, if your plan fails IRS nondiscrimination (ACP) testing, the plan can refund your after-tax contributions in the spring with the earnings taxable. Third, if you don’t convert quickly, the earnings on after-tax money are taxable at conversion, which erodes the benefit. Set up automatic conversions the same pay period the contributions go in.

One more thing: this strategy only lives inside plans that opt in. If yours doesn’t, ask HR to add the feature. Sometimes they will.

The post The Mega Backdoor Roth: How Some 401(k)s Let You Stash $70,000+ a Year Into Tax-Free Retirement Money appeared first on 24/7 Wall St..