By Carmine Coppola, Co-Founder, Strata Capital
Retirement is expensive. Not in a vague, theoretical way, but in the very real sense that replacing your income without a paycheck takes planning, discipline, and time. Most people hear the standard guidance early in their careers: save consistently, take advantage of the match, invest for the long term.
Then life happens.
Compensation changes. Costs rise. Kids, housing, and family responsibilities expand. Even strong savers can fall behind their targets for a period of time. That is not a character flaw. It is reality.
The question becomes practical: what can you do if you are doing “the basics” and still want to save more in a tax-smart way?
In a video I recorded, I break down one of the most underused features inside many employer retirement plans: after-tax 401(k) contributions. This is not the same thing as Roth. It is not the same thing as pre-tax. It is a third bucket that, when used correctly, can meaningfully expand how much you can put away each year and, in certain plan designs, can create a path to more tax-free growth.
Click here to watch the full video
This strategy is not for everyone. But for the right person with the right plan, it can be a serious lever.
The Three Types of 401(k) Contributions
Most people are familiar with two options inside their 401(k).
Pre-tax contributions reduce taxable income today. The tradeoff is that withdrawals in retirement are generally taxable as ordinary income.
Roth 401(k) contributions are made with after-tax dollars. The benefit is that qualified withdrawals in retirement may be tax free, assuming the rules are met.
After-tax 401(k) contributions are different. You contribute money after paying income tax, similar to Roth contributions. But unlike Roth contributions, after-tax dollars go into a separate source within the plan. Growth inside that after-tax source is tax deferred while it remains in the plan. The value comes from what you can potentially do next.
In certain plans, after-tax contributions can be converted into Roth dollars. When the conversion is done efficiently and with the right timing, it can position future growth to be tax free.
That is the core concept behind the mega backdoor Roth.
Why After-Tax Contributions Matter
The most important reason after-tax contributions matter is that they can allow higher total annual savings than most people realize.
The employee deferral limit, meaning the amount you can contribute as pre-tax or Roth, is one number. The overall 401(k) limit, including employer contributions and other permitted sources, is a different number.
For 2026, the pre-tax and Roth employee contribution limit is $24,500. For those age 50 and older, a catch-up contribution increases that amount. For individuals in certain age ranges, higher catch-up rules may also apply.
The key point is that the total 401(k) limit is higher than the employee deferral limit. In 2026, that overall limit can reach $72,000, and in some cases higher depending on age-based catch-up rules and plan provisions.
That gap between what most people contribute and what the plan can actually accept is where after-tax contributions may come into play.
If someone is already maxing out their pre-tax or Roth contribution and still has capacity to save more, after-tax contributions can create an additional lane inside the same plan.
This is one of the reasons the strategy is often overlooked. Many people assume once they hit the employee limit, there is nothing else to do. In some plans, there is more room.
The Mega Backdoor Roth Connection
After-tax contributions become significantly more interesting when a plan allows conversion. This is commonly referred to as the mega backdoor Roth strategy.
Here is the concept in plain terms.
After-tax contributions go into the 401(k) already taxed. If the plan permits, those after-tax contributions can be converted to Roth, either inside the plan or by moving them to a Roth IRA through an eligible distribution process.
When done correctly, the goal is to convert the after-tax dollars before meaningful earnings build up. Earnings generated before conversion may be taxable upon conversion, depending on the structure and timing. That is why timing matters. Waiting too long can create unnecessary tax complexity.
This is one place where the strategy can go sideways. It is not enough to contribute after-tax dollars. The sequence, timing, and plan features determine whether the mega backdoor Roth is clean and efficient.
When the mechanics are coordinated properly, the result is powerful. More dollars are moved into a Roth environment, and future growth may be positioned to be tax free under qualified distribution rules.
A Simple Example of the Impact
Examples help make this real, but they are only illustrations. Actual results depend on contribution levels, investment performance, timing, fees, and tax rules.
In the video, I used a simplified scenario: $12,000 of after-tax contributions each year over 20 years, assuming a 7% average annual return.
In one scenario, the contributions stay in the 401(k) as after-tax and are not converted. In another scenario, the after-tax contributions are converted to Roth, allowing future growth to potentially be withdrawn tax free under Roth rules.
The point is not the exact ending balance. The point is that the tax treatment of growth can change the outcome meaningfully over time. When you can position a large pool of assets for tax-free growth, that can expand flexibility in retirement planning.
This is one of the reasons we focus on tax diversification. It is not just about saving more. It is about saving in ways that create more options later.
Employer Match and Plan Variations
One more variable that matters is how the employer match is treated.
Some plans may match after-tax contributions, while others may not. Some plans match only the first portion of employee deferrals. Some match formulas are based on total contributions, while others are based on pre-tax or Roth deferrals only.
If a plan matches after-tax contributions, that can meaningfully increase the value of the strategy. If it does not, after-tax contributions can still be valuable, but the analysis changes.
This is why plan design matters so much. Two people working at different companies can be following the same idea and have very different outcomes, purely based on plan rules.
Checking plan documents and confirming features with a benefits team can be an important first step. It is also where a coordinated advisor can help, because the fine print is often where the opportunity lives.
When After-Tax Contributions Make Sense
This strategy is not a starting point. It is a layering strategy.
Before considering after-tax contributions, I typically want people to pressure-test a few fundamentals.
Pre-tax or Roth 401(k) contributions should generally be prioritized first, especially if the employer match is available.
A stable emergency fund matters. Retirement savings should not create unnecessary cash flow stress.
Debt and liquidity considerations should be evaluated. A strong plan does not just maximize contributions. It balances stability, flexibility, and long-term growth.
Then the plan features need to be confirmed.
Does the plan allow after-tax contributions?
Does the plan allow in-plan Roth conversions, or in-service distributions that can be rolled into a Roth IRA?
How frequently can conversions be done?
How are earnings treated?
Are there administrative or recordkeeping limitations?
Those answers determine whether after-tax contributions are simply additional savings or whether they can serve as a bridge to a mega backdoor Roth.
What to Watch Out For
The biggest issues I see fall into three categories: plan limitations, timing, and coordination.
Plan limitations are straightforward. Not every plan allows after-tax contributions. Not every plan allows conversions. Some plans allow them but limit how often. Some plans add administrative friction that makes the strategy harder to execute consistently.
Timing matters because earnings can build quickly. The longer after-tax contributions sit unconverted, the more earnings may accumulate, and those earnings may be taxable during conversion. This does not always make the strategy wrong, but it can reduce efficiency and add complexity.
Coordination matters because after-tax contributions are not a standalone decision. They are part of a broader picture involving income planning, tax strategy, investment allocation, and long-term retirement goals.
This is especially important for people with variable compensation, equity awards, or a high household income. The goal is not just to save more. The goal is to save in the right places, with the right tax treatment, and with a clear plan for how assets will be used later.
The Strategy Behind the Strategy
When people hear “mega backdoor Roth,” they often assume it is either a loophole or something overly complex. In reality, the concept is simple.
Many people are limited by the employee deferral cap. After-tax contributions can open additional room. A conversion feature can shift those dollars into Roth treatment.
That is the strategy.
The sophistication is not in the idea. It is in the implementation. The strongest results tend to come from a consistent process, clear tracking, and a coordinated view of taxes and investments.
That is what we aim to deliver at Strata Capital. Sophisticated planning is not about complexity for its own sake. It is about making sure the tools you already have are being used intentionally.
Closing Thoughts
Retirement readiness is not just about what you earn. It is about what you keep, how you invest it, and how efficiently you position it for the future.
After-tax 401(k) contributions are a great example of an overlooked planning tool. For the right person, they can add meaningful capacity to save. For the right plan design, they can create a path to more tax-free growth.
The best next step is not to assume this strategy applies. The best next step is to confirm plan features, review your current contribution levels, and determine whether this is an appropriate layer within your broader plan.
If you do that work, you may find a planning opportunity that has been sitting in your benefits package the entire time.