If your employer lets you sock away more than the standard 401(k) limit, there's a strategy that quietly builds a tax-free pile for retirement.
It's nicknamed the mega backdoor Roth, and it has nothing to do with the regular Roth IRA most people know.
In 2025, you can put up to $23,500 into a 401(k) from your paycheck, or $31,000 if you're 50 or older.
But the total cap on all contributions to a workplace plan, including what your employer kicks in, is $70,000.
That leaves a wide lane for extra savings that many workers never use.
The catch is that your specific plan has to allow it.
You need two features: the ability to make after-tax contributions, and the option to convert that money into Roth dollars, either inside the plan or by rolling it to a Roth IRA.
Plenty of big employers offer this, but they rarely advertise it.
You usually have to dig through the plan documents or call the benefits line.
Regular 401(k) money gets taxed when you withdraw it in retirement.
Roth money comes out tax-free, as long as you follow the rules.
So every dollar you move into Roth treatment now is a dollar the IRS can't touch later.
For high earners who are locked out of normal Roth IRAs by income limits, this is one of the few legal doors still open.
After-tax contributions don't get you a tax break today, so you need cash flow to spare.
The conversion itself can trigger taxes on any earnings that piled up before you moved the money, which is why many people convert quickly, sometimes automatically with each paycheck.
And the $70,000 ceiling includes every dollar from you and your employer combined.
The mechanics trip people up, so a few phone calls are worth it.
Ask your HR or plan provider three questions: Do we allow after-tax contributions?
Do we allow in-plan Roth conversions or in-service rollovers?
If the answer to the first two is yes, you can usually set it up online in a few minutes.
One more wrinkle: not every plan permits this, and some that do charge fees or limit how often you can convert.
If yours doesn't offer it, that's not a reason to panic.
You can still max out a regular 401(k), fund a Roth or traditional IRA if you qualify, and park money in a taxable brokerage account.
The tools differ, but the habit of saving consistently matters more than any single loophole.
Our take: this is one of the more generous breaks left in the tax code, and it's wasted on people who never ask about it.
Spend ten minutes checking your plan's rules before the year runs out.
Final Thoughts
If it's available and you can afford it, using it beats wishing you had later.