Most Americans know the standard Roth IRA caps out at $7,000 a year, or $8,000 if you're 50 or older.
But a lesser-known wrinkle in the tax code lets some workers sock away far more — up to $46,000 in 2024 — inside a Roth account.
It's nicknamed the "mega backdoor Roth," and it's quietly becoming a favorite move for people who max out their regular 401(k) and still want more tax-free growth.
Your 401(k) has an annual contribution limit of $69,000 in 2024, counting both your money and your employer's match.
If you only put in $23,000 (the standard employee limit), that leaves a big gap.
Some plans let you fill that gap with after-tax dollars, then convert that money into Roth.
Because you already paid tax on it, the conversion is usually cheap or free — and future growth comes out tax-free in retirement.
The catch is that your employer's plan has to allow it.
Not every 401(k) offers after-tax contributions, and even fewer allow the in-plan conversions that make this smooth.
Fidelity, Vanguard, and other big administrators have added the feature, but it's far from universal.
If your plan doesn't support it, there's no workaround — you can't do this with an IRA on your own.
If your plan does allow it, the mechanics matter.
You typically contribute after-tax money to your 401(k), then either convert it to a Roth 401(k) or roll it into a Roth IRA.
Doing this regularly — say, every pay period — limits the taxable growth that builds up before conversion.
Letting after-tax money sit for years means a bigger tax bill when you finally convert, since earnings are taxed as ordinary income.
The upsides are real for high earners who are locked out of normal Roth IRAs due to income limits.
The mega backdoor route lets them build a tax-free bucket that can grow for decades.
For someone in their 30s or 40s, that's a meaningful chunk of retirement money that won't be taxed on the way out.
You need the cash flow to contribute well beyond your normal 401(k) max, which most households don't have.
You also need to watch plan fees, investment options, and whether the conversion triggers any paperwork headaches at tax time.
A CPA or fee-only advisor can tell you if the math works in your situation.
A few practical steps if you want to explore it: Log into your 401(k) account and search for "after-tax contributions" or "in-plan Roth conversion." If you don't see it, call your plan administrator and ask directly.
And check the current-year IRS limits, since they adjust for inflation and the numbers shift every year.
One more thing worth knowing: the mega backdoor Roth is legal and has survived repeated tax-law changes, but Congress has tinkered with retirement rules before.
Rules could shift, so it's worth using the feature while it's available rather than assuming it will always be there.
The bottom line: this isn't a magic trick, and it won't help anyone who isn't already saving aggressively.
But for a certain slice of workers — decent income, a supportive 401(k) plan, and a long time horizon — it's one of the few remaining ways to shelter a serious amount of money from future taxes.
Final Thoughts
If you've maxed out everything else and still have room to save, it's worth a call to your plan provider.