What's A Mega Backdoor Roth?
If you like your Roth IRA for its tax-free growth, you’re really going to like a mega backdoor Roth! Contributions to a Roth IRA are funded with after-tax dollars and earnings grow entirely tax-free. Similarly, a mega backdoor Roth is also funded with after-tax dollars and earnings grow tax-free but with a much higher contribution limit!
Editor’s Note: This post was originally published in November 2021 and has been updated in December 2023 for accuracy.
Roth IRA and 401(k) Limits
Before we learn more about the mega backdoor Roth, it’s important to understand the tax benefits and differences between a Roth IRA and a 401(k), their income restrictions, and their contributions limits. If you’ve read my Roth IRA or 401(k) post, you’ll know that the only reason to consider a Backdoor IRA is if your income exceeds a certain threshold. Performing a Backdoor IRA conversion works around those income restrictions and allows anyone in any tax bracket to max out a Roth IRA with $7,000 in after-tax dollars. For those 50 or older, the catch-up limit is $1,000, so contributions max out at $8,000.
As long as your employer offers a 401(k) plan, anyone can contribute to a 401(k), regardless of your income level. Employees have a contribution limit of $23,000 as of 2024. Thankfully, employer match contributions don’t count toward that limit, but there is a combined employee + employer 401(k) contribution limit of $69,000. For those 50 or older, the catch-up limit is $7,500, bringing the total employee + employer 401(k) contribution limit to $76,500.
It’s an understatement to say that the combined employee + employer 401(k) contribution limit of $69,000 is quite high. So that begs the question, “How does anyone ever reach those limits?” Well, there are two ways, but only one of them can realistically get you there.
Employer Match Contributions
Employees can contribute up to $23,000 of the combined max of $69,000. That leaves a max employer contribution of $46,000. However, most employers don’t even get close to contributing the full amount. A good match is typically around 4% of your base salary. So reaching the 401(k) cap with employer contributions is usually not enough on its own.
For example, let’s say you make $100,000, max out your 401(k) with $23,000 of your pre-tax dollars, and your employer match contribution is 100% of your 401(k) contributions, up to 4% of your base salary. That would look like:
Employee contribution: $23,000
Employer match: $100,000 x 4% = $4,000
Total 401(k) contributions: $23,000 + $4,000 = $27,000
Subtracting $27,000 from the max 401(k) contribution limit of $69,000 leaves $42,000 remaining, which is why employer match contributions won’t realistically be enough to help you reach the combined max. Luckily, if your employer’s 401(k) plan allows after-tax contributions, you can do a mega backdoor Roth to make up the remainder!
Mega Backdoor Roth
Before diving into how to do a mega backdoor Roth, there are some prerequisites and considerations to highlight:
Your employer’s 401(k) plan needs to allow after-tax contributions. Without this option, you can’t do a mega backdoor Roth. Check with your employer’s HR team to find out if they offer this benefit.
Your employer’s 401(k) plan allows for “in-service” withdrawals to a Roth IRA or “in-plan” rollovers to a Roth 401(k). If neither is offered, you can’t touch your after-tax contributions in your 401(k). Therefore, your earnings would grow tax-deferred, not tax-free! In that case, I’d recommend avoiding the mega backdoor Roth altogether. It’s actually worse to invest after-tax dollars in a 401(k) than a regular brokerage account because 401(k) withdrawals are taxed as ordinary income, not (long-term) capital gains!
If you haven’t maxed out your 401(k) with pre-tax dollars, do that first.
No matter what your income is, you can do a mega backdoor Roth. There’s no minimum contribution amount, but there is a max.
In order to max out a mega backdoor Roth, you need to have a relatively high income. Why? Because maxing out a mega backdoor Roth would require up to $42,000 of post-tax dollars. That’s what puts the “mega” in mega Backdoor Roth! Its younger sibling, the backdoor IRA, maxes out at $7,000.
On the last point, remember that we’re trying to utilize the combined employee + employer 401(k) contribution limit of $69,000. If your employer contributes $4,000 to your 401(k), for example, your total contributions (pre-tax + post-tax dollars) would come out to $65,000! To illustrate, let’s assume you make $100,000 per year as a single filer and see what this looks like:
| Gross Income | $100,000 |
|---|---|
| Pre-tax 401(k) contributions | ($23,000) |
| Income after 401(k) contributions | $77,000 |
| Federal standard deduction (single) | ($14,600) |
| Federal taxable income | $62,400 |
| FICA (6.2% Social Security tax, 1.45% Medicare tax) | ($3,869) |
| 2024 Federal taxes (14.07% effective tax rate) | ($8,781) |
| After-tax 401(k) contributions | ($42,000) |
| Take-home income | $77,000 - (taxes) - (after-tax 401(k) contributions) = $22,350 |
So in this scenario, a single filer making $100,000 annually who maxes out their traditional 401(k) with both pre-tax and post-tax dollars is only left with $22,350 assuming no state taxes and before expenses!
Alright, now let’s finally talk about how to do a mega backdoor Roth. First, you’ll need to reconfigure your 401(k) contributions with your brokerage firm so that it not only contributes pre-tax dollars towards your traditional 401(k), it now needs to contribute after-tax dollars towards, too. Remember that if you’re just starting to contribute post-tax dollars partway through the year and want to max out your mega backdoor Roth, the math isn’t as simple as ($69,000 - $23,000 - employer match contributions) divided by (# of paychecks in a year); instead of dividing by (# of paychecks in a year), it now becomes (# of remaining paychecks this year), which can amount to a massive reduction in take-home pay.
Now that you’re contributing after-tax dollars to your 401(k), there’s really only 1 more step. As I mentioned in point #2 in the prerequisites above, your 401(k) needs to allow for “in-service” withdrawals to a Roth IRA or “in-plan” rollovers to a Roth 401(k):
In-service withdrawals: This would require you to manually call your 401(k) brokerage firm, like Fidelity or Vanguard, every time you want to convert your after-tax dollars to your Roth IRA.
In-plan rollovers: This is the much simpler approach to setting up a mega backdoor Roth. You only have to call your brokerage firm, like Fidelity or Vanguard, one time and have them set up automatic rollovers of your 401(k) after-tax contributions into your Roth 401(k). So as soon as your contributions are taken from your paycheck and land in your 401(k), they’ll automatically get rolled into your Roth 401(k).
To summarize the two options:
| In-Service Withdrawals to a Roth IRA | In-Plan Rollovers to a Roth 401(k) |
|---|---|
| Hands-on approach | Hands-off approach |
| Requires calling brokerage firm every withdrawal | One-time setup |
| Manual process may lead to accrued earnings in 401(k), requiring you to pay taxes on earnings when you withdraw | Automatic approach avoids 401(k) earnings before the conversion, thereby avoiding having to pay any taxes on each rollover |
| Large range of investment options | Limited by your employer's 401(k) investment options |
That’s it. Now you know how to do a mega backdoor Roth and can watch your earnings grow tax-free!
One last cautionary note before doing any backdoor Roth conversion: Be careful not to mix after-tax dollars with pre-tax dollars in retirement accounts, as you may be subject to tax consequences due to pro-rata rules. Talk to a professional if you need assistance.
Can I Do Both A Backdoor IRA and A Mega Backdoor Roth?
Yes! You can max out your Backdoor IRA and mega Backdoor Roth in the same year. A Backdoor IRA utilizes IRA contributions, and a mega Backdoor Roth utilizes 401(k) contributions. The sum of all your IRA contributions maxes out at $7,000 per year, and the sum of all your 401(k) contributions maxes out at $69,000 per year.
Summary of Income and Contribution Limits
As of 2024, the income and contribution limits for each type of retirement account are:
401(k):
No income restrictions
$23,000 contribution limit
$7,500 catch-up limit if 50 or older
Roth IRA:
$161K (single) and $240K (married filing jointly) income limits
$7,000 contribution limit
$1,000 catch-up limit if 50 or older
Mega Backdoor Roth:
No income restrictions
$46,000 contribution limit. If your employer has a 401(k) company match, this limit decreases for every dollar your employer contributes to your account.
It’s important to note that catch-up contributions to a 401(k) or Roth IRA don’t count toward their respective contribution limits. So the total combined contribution limits looks like:
Traditional 401(k) + Roth 401(k) + Roth IRA = $23,000 + $46,000 + $7,000 = $76,000
For those 50 or older, we can add the catch-up amounts: $76,000 + $7,500 + $1,000 = $84,500
If you and your spouse work for employers with mega backdoor Roth options, then double the amounts to $152,000. And for those 50 or older, the cap goes to a whopping $169,000 per year!
As I mentioned earlier, maxing out a mega backdoor Roth demands quite a high income, given how much you could potentially contribute. You obviously don’t need to completely max out your account, so do what you can. Also, if you’re considering a mega backdoor Roth, you probably need to do a regular backdoor IRA, too. You may want to max out that account first before doing the mega since it’s slightly more straightforward. Ultimately both options result in the same tax-free growth, so the choice is yours!
Announcements
I recently launched a new “Resources” section where I plan to add helpful tools and guides! Check it out now! I’ve created 2 new pages:
A page highlighting some of the top employers’ 401(k) benefits
A step-by-step guide on how to do a regular Backdoor IRA using Fidelity!
