Somewhere in a benefits portal most employees never scroll past, there's a line item that lets you stash up to $46,000 extra into retirement accounts this year.
And roughly 30,000 people use it, according to IRS data estimates — a rounding error next to the 60 million Americans with 401(k)s.
It's called the mega backdoor Roth, and the name is doing it a disservice.
There's no backdoor, nothing shady, and the IRS has effectively shrugged at it for a decade.
What it actually is: a three-step maneuver that converts after-tax 401(k) contributions into Roth dollars, bypassing the income limits that lock high earners out of regular Roth IRAs.
Your employer's plan has to allow two things: after-tax contributions (not Roth, not pre-tax — after-tax), and either in-plan conversions or in-service withdrawals.
If both boxes are checked, you contribute past the $23,000 pre-tax limit, then immediately convert that money to Roth.
You pay income tax on any growth between contribution and conversion, which is usually pennies if you convert fast.
The catch is that most plans don't allow this.
A 2023 survey from the Plan Sponsor Council of America found only about 23% of 401(k) plans offered after-tax contributions at all, and fewer still permit the conversion step.
So the first move is boring: log into your portal, download the summary plan description, and search for "after-tax." If it's not there, you're done.
If it is there, the math gets interesting.
Total 401(k) contributions — you plus your employer — cap at $69,000 in 2024, or $76,500 if you're 50 or older.
Most people hit the $23,000 employee limit and stop.
The mega backdoor lets you fill the remaining space, which for a high earner with a generous match can mean another $30,000 to $40,000 a year in tax-advantaged savings.
People who already max out their 401(k), have cash flow to spare, and work at companies with plans designed by firms like Fidelity or Vanguard that offer the feature.
Someone earning $60,000 with a 3% match has neither the plan nor the spare cash.
And here's the part advisors gloss over: doing this requires you to lock money away until 59½, with limited exceptions.
If you're saving for a house or a kid's tuition, dumping $30,000 into a Roth 401(k) isn't smart — it's illiquid.
The tax break is real, but it's not free money.
Some plans require you to call to convert after every paycheck, because automated conversions aren't set up.
Miss a few paychecks and the gains pile up, generating a tax bill at conversion.
Run the numbers before assuming the strategy is a slam dunk.
The mega backdoor Roth is a legitimate tool that most people can't access, and the ones who can often already have plenty of retirement runway.
It's worth checking your plan document — but treat it as a bonus if it's there, not a reason to feel behind if it isn't.
Final Thoughts
It's how quietly the tax code rewards employees at certain companies and leaves everyone else reading headlines about a trick they'll never qualify for.