Skip to Content
Investing Specialists

The Time Is Right for Aftertax 401(k) Contributions

The prospect of higher taxes and the uptake of in-plan conversions make this maneuver a no-brainer for heavy savers who have access to it.

For higher-income investors, the "backdoor Roth IRA" maneuver has become an annual ritual--a way to get money into a Roth IRA account even if they earn too much to make a direct Roth IRA contribution.

But high-income, heavy-saving investors should also take a look at aftertax 401(k) contributions, which, when rolled into an IRA, become what is sometimes called a "mega-backdoor Roth." Much like the basic backdoor Roth IRA, this strategy involves aftertax contributions--in this case, to a 401(k)--and then converting them to Roth at some later date.

One of the key benefits of aftertax 401(k) contributions is that they are allowable on top of the basic traditional or Roth contributions, making them ideal for heavy savers looking for additional opportunities for tax-advantaged savings. While aftertax contributions aren't available to everyone with a 401(k), plans that do offer them are increasingly adding features that make it easy to convert those contributions to Roth without leaving the plan.

Factoring in the tax benefits, aftertax 401(k) contributions beat what is usually the only other alternative for heavy savers who have maxed out their retirement accounts: investing in a taxable brokerage account. Moreover, potential changes to the tax treatment of nonretirement account assets--specifically, a higher capital gains tax rate and limitations on the unlimited "step-up" in cost basis that such accounts currently enjoy--would further embellish the appeal of the mega-backdoor Roth IRA maneuver.

Roth 401(k) > Aftertax 401(k)

While roughly three fourths of 401(k) plans now allow Roth 401(k) contributions, aftertax 401(k) contributions are less common. According to Vanguard's 2020 "How America Saves" report, just 18% of Vanguard plans offered aftertax contributions in 2019, and that figure hadn't budged since 2015. As with many 401(k) creature comforts, aftertax contributions are mainly available through the plans of larger employers.

One common point of confusion is how aftertax contributions differ from Roth contributions. After all, investors contribute aftertax dollars to Roth accounts, too. But there are a few key differences, one related to contribution limits and the other to tax treatment.

First, the contribution limits: While investors can contribute $19,500 ($26,000 if they're over age 50) to a Roth or traditional/pretax 401(k) account, aftertax 401(k) contributions are even more generous. There's no specific dollar amount for aftertax 401(k) contributions, but total 401(k) contributions, including traditional/Roth contributions, employer contributions, forfeitures, and aftertax contributions, can go as high as $58,000 in 2021 ($64,500 for people 50-plus). For example, let's say a 45-year-old contributed $19,500 and received an additional $9,750 in matching funds from his employer. In that instance, he could contribute an additional $28,750 to the aftertax 401(k) before hitting the $58,000 ceiling for total 401(k) contributions.

But despite the generous contribution limits on aftertax 401(k)s, it's important to understand that there's no reason to make aftertax contributions before maxing out Roth contributions first (or traditional pretax contributions, for that matter).

Why is the Roth 401(k) better? The saver contributes aftertax dollars to both accounts. But while Roth contributions enjoy tax-free compounding beginning on day 1, aftertax 401(k) contributions compound on a tax-deferred basis. (Tax-deferred means that at least part of the assets will be taxable upon withdrawal, whereas tax-free is just what it sounds like.) Only when the employee retires, leaves the company, or the plan allows for what's called an "in-plan conversion," can the employee convert the aftertax contributions to a Roth account. Any investment earnings that have built up in the account can be rolled over to a traditional tax-deferred IRA, where those assets will be taxed upon withdrawal. In essence, the aftertax 401(k) maneuver allows contributors to amass tax-deferred assets, and the contributions to the account can become Roth assets at some later date. But the tax savings aren't as great with an aftertax 401(k) as they are with Roth or traditional 401(k)s.

What's interesting, though, is that many plans that offer aftertax 401(k)s also offer in-plan conversions, which reduces the extent to which assets might rack up gains that are subject to taxation upon conversion. Better yet, some plans have begun offering automatic conversions. That means the participant doesn't have to manually execute the conversions; rather, he or she can elect to have aftertax dollars convert automatically. That greatly reduces what had been one of the key "pain points" of aftertax contributions.

Aftertax Contributions > Taxable Contributions

For high-income savers who have access to aftertax 401(k) contributions, fully funding the 401(k) up to the $58,000/$64,500 limit will tend to beat saving in a taxable account, especially if the investor has a good-quality plan and doesn't need the liquidity of the taxable account. That's because the tax drag on the aftertax 401(k) account is much less, particularly if in-plan conversions are available.

To illustrate, let's assume a 42-year-old is maxing out all of the tax-sheltered options she can get her hands on, but she still has another $10,000 per year in aftertax dollars available to invest for the next 25 years prior to retirement. She earns a 5% annualized return on her money over the 25-year period.

If she invested in a taxable account, we'd have to shave her annualized return, at least a bit, to account for the fact that she's subject to dividend and capital gains taxes during her accumulation period. Assuming a modest tax-cost ratio 0.5%, that takes her annualized return down to 4.5%. At the end of the 25-year period, her brokerage account would have grown to $454,592. If she were to begin withdrawing the money after 25 years, she'd owe capital gains taxes on the $204,592 of the account that represents investment appreciation. (She won't be taxed on her $250,000 in contributions again, because she made them with aftertax money.) Assuming a 15% capital gains tax rate (and it would actually be a bit lower because she has paid some taxes already), she'd have an aftertax balance of $423,903 available after 25 years.

If she invested that same $10,000 in an aftertax 401(k) for 25 years and executed regular conversions (better yet, automatic ones), she'd earn the full 5% on her money over that time frame. And unlike the taxable account, she won't have to pay taxes on her money as it grows. (Dividends and capital gains distributions aren't taxed on a year-by-year basis as long as the money stays inside the tax-deferred account.) She'd have $487,920 in the account after 25 years. And assuming she has conducted regular conversions, those funds would be entirely tax-free--more than $60,000 more than if she had stuck with the taxable brokerage account.

Those tax savings would be magnified at higher contribution levels, higher rates of return, over longer time frames, or for investors who are in a higher capital gains bracket than 15%. And if a proposal to increase the highest capital gains rate were to become law, aftertax 401(k) contributions would be even more attractive than investing in a taxable account for savers who would otherwise be subject to that higher rate.

Amassing assets in an aftertax 401(k) would also be more attractive relative to investing in a taxable account if another tax proposal under consideration--the elimination of the now-unlimited step-up in capital gains--comes to fruition. After all, one of the major tax benefits of investing in a nonretirement account currently is that heirs are allowed to "step up" the value of an inherited asset to its value upon the date of death. If the amount of assets eligible for the step-up were dramatically curtailed, as is currently under consideration by Congress, inheriting taxable assets would be less advantageous than is the case today. Meanwhile, inherited Roth assets would remain tax-free.

What's Not to Love?

As attractive as aftertax 401(k) contributions are from a tax standpoint, they're not the right answer in every situation. As mentioned earlier, investors who need access to their funds without any strictures will be better off investing in a taxable brokerage account. And 401(k) plans that allow for aftertax contributions but don't include an in-plan conversion feature will also be less attractive, in that the aftertax assets can't be rolled into a Roth account until the participant has retired or separated from service. 

The quality of the 401(k) plan is another important variable. While aftertax contributions are generally the domain of larger employers, which often field solid investment lineups and feature low fees, offering an aftertax option is no guarantee of plan quality. Thus, if a 401(k) plan isn't great, that can reduce the tax-saving benefits relative to investing in tax-efficient, low-cost investments inside of a taxable brokerage account. 

Transparency is how we protect the integrity of our work and keep empowering investors to achieve their goals and dreams. And we have unwavering standards for how we keep that integrity intact, from our research and data to our policies on content and your personal data.

We’d like to share more about how we work and what drives our day-to-day business.

We sell different types of products and services to both investment professionals and individual investors. These products and services are usually sold through license agreements or subscriptions. Our investment management business generates asset-based fees, which are calculated as a percentage of assets under management. We also sell both admissions and sponsorship packages for our investment conferences and advertising on our websites and newsletters.

How we use your information depends on the product and service that you use and your relationship with us. We may use it to:

  • Verify your identity, personalize the content you receive, or create and administer your account.
  • Provide specific products and services to you, such as portfolio management or data aggregation.
  • Develop and improve features of our offerings.
  • Gear advertisements and other marketing efforts towards your interests.

To learn more about how we handle and protect your data, visit our privacy center.

Maintaining independence and editorial freedom is essential to our mission of empowering investor success. We provide a platform for our authors to report on investments fairly, accurately, and from the investor’s point of view. We also respect individual opinions––they represent the unvarnished thinking of our people and exacting analysis of our research processes. Our authors can publish views that we may or may not agree with, but they show their work, distinguish facts from opinions, and make sure their analysis is clear and in no way misleading or deceptive.

To further protect the integrity of our editorial content, we keep a strict separation between our sales teams and authors to remove any pressure or influence on our analyses and research.

Read our editorial policy to learn more about our process.