You're maxing your 401(k). You've got the backdoor Roth IRA on autopilot. You're funneling the leftover cash into a taxable brokerage account where every dividend and rebalance shows up on your tax return. And somewhere in the back of your mind you've got the nagging sense there should be a better home for that money.
There is one. It's called the mega backdoor Roth, and if your employer's plan supports it, you can move tens of thousands of dollars a year into a Roth account where the growth never gets taxed again. Not "tax-deferred." Tax-free.
Everything turns on that conditional. Most of this post is about finding out where your 401(k) plan stands, and how to run the strategy cleanly if it clears.
Why This Is a Tech-Employee Strategy
The mega backdoor Roth (we'll call it MBR) isn't for everyone, and that's not a marketing line: it's a function of cash flow. The strategy only works if you've already filled the cheaper buckets and still have money left to contribute. That describes a narrow slice of the workforce and a wide slice of senior tech.
It tends to fit best when you:
Are in a high marginal bracket, so tax-free growth is worth more to you than to most people
Already max your 401(k) and have an emergency fund you're not nervous about
Have surplus cash flow: often the case when base salary covers your life and equity comp is gravy
Want to shift dollars out of a taxable brokerage and into a wrapper that stops generating a tax bill every year
That last point is the one people underrate. If your "extra" savings currently live in a taxable account, you're paying tax on dividends and capital gains along the way. The MBR doesn't just add a Roth bucket. It relocates money you were going to save anyway into a better-taxed home. It's especially useful if you got a late start on retirement savings and you're trying to make up ground fast.
How the Mega Backdoor Roth Works
The whole strategy lives inside one number most people have never heard of: the total 401(k) contribution limit.
In 2026, the most you can defer into your 401(k) as an employee is $24,500 (or $32,500 if you're 50 or older, thanks to the catch-up). But the IRS sets a much higher ceiling on what can land in your 401(k) from all sources combined: your contributions, your employer's match, and after-tax contributions. That combined limit is $72,000 in 2026.
The gap between those two numbers is the opening.
Here's the 2026 math, with and without the age-50 catch-up:
The table uses the age-50 catch-up of $8,000 to keep the illustration simple. If you're 60 to 63, SECURE 2.0 sets yours at $11,250 instead, lifting your deferral limit to $35,750 and the combined ceiling to $83,250.
The after-tax room reads $37,500 in every column, and that isn't a coincidence. The catch-up raises the combined ceiling and your own deferral by the same amount, so it never changes the gap the MBR fills. Age changes how much you can defer. It doesn't change what's left for after-tax.
That bottom row is the mega backdoor Roth. You make after-tax contributions to fill the gap, then convert them to a Roth account. Because you already paid tax on those dollars before they went in, the conversion itself isn't a taxable event. But once the money is sitting in a Roth, all the future growth and qualified withdrawals come out completely tax-free.
It helps to see why the after-tax bucket is the odd one out. Here's how the three contribution types get taxed:
Look at that bottom-right cell. After-tax contributions get the worst of both worlds if you leave them alone: you pay tax going in and the growth gets taxed coming out. That's why the after-tax bucket is a holding pen, not a destination. You convert it to Roth, and that final cell flips from "taxed" to "tax-free." The conversion is the entire point.
Which is also why timing matters, but more on that below.
Step One: Does Your Plan Even Allow This?
Before you get excited, this is the gate that stops most people. The mega backdoor Roth depends on two plan features that the IRS permits but doesn't require. Your employer chooses whether to offer them.
First question: does your plan allow after-tax contributions?
Not Roth contributions: after-tax contributions. They're different things, and the distinction is exactly where people get confused. You'll find the answer in the "Contributions" section of your 401(k)'s Summary Plan Description (SPD). If after-tax contributions are allowed, keep reading. If they're not, the strategy is dead on arrival and you can stop here.
Second question: are you allowed to make them?
This is the part that trips up high earners specifically. Many plans block Highly Compensated Employees (HCEs) from making after-tax contributions, because letting them do so would cause the plan to flunk an IRS fairness test (the Actual Contribution Percentage test, if you want the technical name).
For 2026, you're an HCE if you either:
Owned more than 5% of the company at any point in the prior year, or
Earned more than $160,000 in the prior year (some employers further limit HCE status to the top 20% of earners, an optional election)
If you're a senior engineer or PM at a tech company, you're almost certainly an HCE. That means this gate is the one most likely to bite you. Two things to know:
Solo 401(k)s have no ACP test, so business owners and consultants get a clean shot at this
If your after-tax contributions cause the plan to fail the test, you'll get a refund of part of your contribution (and a few people in HR will quietly resent you)
That gate is easier to clear than it sounds, though. The ACP test doesn't bar HCEs from contributing after-tax; it limits how far the HCE average can run ahead of the non-HCE average. Large tech plans are often built so that gap stays inside the limit. Automatic enrollment and a strong match pull non-HCE participation high, which lifts their average and opens room above it. Many plans also cap after-tax contributions at a fixed percentage of pay, so a handful of maximizers can't blow the test for everyone. Some employers make extra contributions for non-HCEs with the same goal. Which of these your plan uses, if any, isn't visible from the enrollment portal.
When you're not sure, ask your HR team, benefits department, or the plan administrator: Fidelity, Schwab, Empower, whoever runs the plan. They've answered this question before.
Step Two: Get the Money Into Roth Before It Grows
Clearing the eligibility gate gets you in the door. Running the strategy well comes down to one more plan feature and a bit of speed.
Remember the bottom-right cell in that table: after-tax contributions go in tax-free, but their growth is taxed as ordinary income. So the goal is simple: convert the contributions to Roth before they have a chance to grow much. The less growth sitting in the after-tax bucket when you convert, the less taxable income the conversion creates.
How you convert depends on what your plan supports:
If your plan allows in-plan Roth conversions: This is the clean version. You convert your after-tax contributions to a Roth 401(k) inside the same plan, ideally right after each contribution. Some plans even automate it: every after-tax dollar gets swept to Roth on a schedule, so no growth ever accumulates in the wrong bucket. If your plan offers this, you're in the best-case scenario.
If your plan allows in-service distributions with separate after-tax subaccounts: You roll only the after-tax money out to a Roth IRA. Again, move quickly to keep the taxable growth minimal. If a little growth tagged along, you can route that piece to a Traditional IRA to defer the tax, though if the growth is small, it's often simpler to just send it to the Roth and pay the modest tax now.
If your plan allows in-service distributions but doesn't separate pre- and after-tax money: This is the messy one. The pro-rata rule kicks in: any distribution gets pulled proportionally from both your pre-tax and after-tax balances. You can still split it: after-tax to a Roth IRA, pre-tax to a Traditional IRA. But you may be forced to move a large chunk of pre-tax money to pull out the after-tax dollars. Doable, but it takes more care, and it's the version where a second set of eyes earns its keep.
One more wrinkle for higher earners: starting in 2026, if your prior-year wages topped $150,000, the SECURE 2.0 Act requires your catch-up contributions to be made on a Roth basis. For most of our clients, that's not a problem. It's a feature. But it's a rule worth knowing before you map out your contributions for the year.
Where the Mega Backdoor Roth Fits the Bigger Picture
Here's the thing about the MBR that a one-off "how-to" misses: it's rarely the first move, and it's never the only one.
The decision of how much to route into after-tax contributions doesn't happen in a vacuum. It runs straight into your equity comp (how much RSU income hits this year, whether you're exercising ISOs), your cash flow (you need real dollars to fund after-tax contributions, and they're locked up once they're in), and your broader tax picture (the catch-up Roth requirement, your marginal bracket). Get the sequencing wrong and you can crowd out a better move.
That coordination is the real work. It's the part most people don't see when they're staring at a 401(k) portal trying to figure out which box to check. The MBR is one square on a much larger board: tax, equity comp, cash flow, and long-term planning all moving at once. Played well across years, a strategy like this builds more than a tax-free balance. It builds a pool of money that no future tax rate gets to touch, which is a different kind of asset from everything else on your statement.
For the broader view of how the pieces fit together, our equity compensation guide walks through how comp, taxes, and savings strategy interact for senior tech employees. And if you want the high-income Roth conversation more generally, how we think about coordinating tax strategy is the place to start.