Most people know the standard Roth IRA limit: $7,000 in 2025, or $8,000 if you're 50 or older.
But a lesser-known maneuver lets some workplace savers shelter tens of thousands more in tax-free growth — and it has nothing to do with the income caps that lock high earners out of regular Roth IRAs.
It's called the mega backdoor Roth, and it lives inside your 401(k) plan.
The catch is that your employer has to offer two specific features, and plenty don't.
For 2025, the total amount you and your employer can put into a 401(k) is $70,000, or $77,500 if you're 50-plus.
That's separate from the $23,500 employee elective deferral limit you probably already know.
The gap between those two numbers — up to roughly $46,500 for most savers — is where the strategy lives.
To exploit it, your plan needs to allow after-tax contributions beyond the standard pre-tax or Roth deferrals, and it needs to let you convert those after-tax dollars into Roth money, either in-plan or by rolling them to a Roth IRA.
If both boxes are checked, you can funnel a huge amount into tax-free territory each year, well above what a normal Roth IRA would ever permit.
Because Roth money grows tax-free and comes out tax-free in retirement, with no required minimum distributions.
For someone in a high tax bracket today who expects lower taxes later — or who simply wants a bigger tax-free bucket — that's an appealing trade.
After-tax contributions don't get an employer match in most plans, and the money you convert is taxed on any earnings that pile up before the conversion happens, so speed matters.
Many people convert immediately or set up automatic same-day rollovers to keep the taxable slice near zero.
If your plan doesn't offer after-tax contributions or in-service conversions, there's no workaround — you'd have to lobby HR or wait for a plan change.
A 2024 survey from the Plan Sponsor Council of America found that a minority of 401(k) plans offer the after-tax feature, so plenty of savers are simply out of luck.
Before diving in, check your plan's summary description or call the administrator and ask two questions: Do you allow after-tax contributions, and can I convert them while still employed?
If the answer to either is no, the strategy is off the table.
One more thing: this isn't a free lunch for everyone.
If you're in a low bracket now, converting could mean paying tax at a rate you'd rather avoid.
And if you might need the money soon, Roth conversions generally aren't the place for short-term cash.
My take: the mega backdoor Roth is one of the few legitimately powerful moves left for diligent savers, but it rewards people whose employers happen to offer the right plan features — which feels less like strategy and more like a lottery.
If you've got access, it's worth a serious look before year-end.
Final Thoughts
If you don't, pressure your plan provider; the rules aren't changing in your favor.