A little-known maneuver is letting high earners stuff tens of thousands more into tax-free retirement accounts every year.
It's called the mega backdoor Roth, and unlike the standard backdoor Roth IRA, it has nothing to do with the $7,000 annual IRA limit.
Instead, it exploits a separate cap buried in workplace retirement plans—and it's perfectly legal.
For 2024, you can contribute up to $69,000 total to a 401(k) across your own deferrals and employer matching.
But your personal pretax or Roth deferral is capped at $23,000 (or $30,500 if you're 50 or older).
That leaves a wide window above your deferral limit that most people never touch.
The mega backdoor Roth fills that window with after-tax money.
If your plan allows it, you contribute after-tax dollars up to the total cap, then convert those dollars into a Roth account—either inside the plan or via an in-service rollover to a Roth IRA.
The earnings grow tax-free from there, and future withdrawals can come out tax-free in retirement.
Two features must exist in your plan for this to work.
First, your employer has to permit after-tax contributions beyond the standard deferral limit.
Second, it has to allow either in-plan Roth conversions or in-service withdrawals.
Many large employers offer both, but plenty don't—and that's the biggest hurdle.
A 40-year-old who funnels an extra $30,000 a year into after-tax contributions and converts it could accumulate hundreds of thousands in additional Roth savings by retirement, all shielded from future taxes.
For high earners already maxing out every other tax-advantaged account, it's the last big bucket available.
You'll owe income tax on any earnings that accumulate before you convert, so converting quickly—ideally immediately—limits the bill.
Some plans restrict how often you can convert.
And because these are after-tax dollars, you don't get a current-year deduction, so you need the cash flow to fund it.
The maneuver is also on Washington's radar.
Lawmakers have debated closing backdoor Roth strategies for years, and while the mega version survived recent tax legislation, the rules could shift.
That uncertainty is one reason some advisors tell clients to use it while it's available.
For most workers, none of this applies—their plans simply don't offer the features.
But if yours does, it's worth a call to your plan administrator or a fee-only advisor.
Ask two questions: Do you allow after-tax contributions above the deferral limit, and can I convert them to Roth?
The answers could change your retirement math.
Our take: the mega backdoor Roth isn't a loophole for the ultra-wealthy so much as a perk for employees lucky enough to have the right plan.
Final Thoughts
If you have the cash flow and the option, the tax-free growth is hard to beat—just confirm the details before assuming your plan qualifies.