If your employer's 401(k) plan allows it, you may be able to stash far more than the standard $23,500 limit into tax-free growth this year.
The catch: almost nobody uses it, and a lot of people who could don't even know it exists.
It's called the mega backdoor Roth, and it's not a scam or a gray-area trick.
It's a set of rules buried in the tax code that lets you move after-tax 401(k) money into a Roth account, where it can grow and come out tax-free in retirement.
In 2025, the total amount that can go into a 401(k) from you and your employer combined is $70,000, or $77,500 if you're 50 or older.
Most people only fill the standard employee portion.
But if your plan permits after-tax contributions, you can keep adding past that point, then convert that money into Roth dollars.
The reason it's called a backdoor is that high earners are normally locked out of Roth IRAs.
This route sidesteps that income cap by going through your workplace plan instead.
The Roth IRA contribution limit doesn't apply here.
Two things have to be true for this to work.
Your plan has to allow after-tax contributions, and it has to allow either in-plan conversions or rollovers to a Roth IRA.
Roughly a third of plans offer this, and it tends to show up at larger employers and tech companies.
Ask your HR department for the plan's summary description and search for the words "after-tax." If you're eligible, the order of operations matters.
First, contribute enough to your regular 401(k) to grab the full employer match.
That's free money and it comes before anything else.
Then, if you still have room in your budget, start adding after-tax dollars.
The second move is the part people mess up.
You want to convert that after-tax money to Roth as quickly as possible, ideally the same day it lands.
If you let it sit and earn interest for years, that growth is taxable when you convert.
Converting right away keeps the tax bill near zero.
If you're carrying high-interest credit card debt, or you don't have an emergency fund, or you're not already saving a healthy chunk for retirement, this is not your next step.
It's a move for people who have maxed out the basics and still have cash left over.
Also worth knowing: the conversion itself doesn't trigger a tax bill on the amount you already paid tax on.
Your plan administrator will send the right forms, and a tax pro can keep the paperwork clean.
There's no deadline drama here, no limited-time offer.
The rules just sit there quietly, year after year, while most people never ask the question.
My take: this is one of the few genuinely valuable perks left in the American retirement system, and it's handed out unevenly.
Final Thoughts
If it doesn't, it's worth asking your benefits team why not.