What is an After-Tax 401(k) and Should You Use it?

If you’ve already maxed out your traditional 401(k) and Roth contributions, or you are looking for ways to accelerate your retirement savings, after-tax 401(k) contributions may be the powerful tool you might be overlooking.

While not as well-known as other retirement options, after-tax contributions can help you invest more, grow more, and create greater flexibility for the future.

But are they right for you or your employees?

Let’s explore how post-tax 401(k) contributions work, their benefits and drawbacks, and how they might fit into your small business financial strategy.

What is an After-Tax 401(k)?

After-tax 401(k) contributions are additional savings you make into your 401(k) after reaching your traditional pre-tax and Roth contribution limits. Unlike pre-tax or Roth contributions, after-tax funds are not tax-deductible, and the earnings grow tax-deferred.

However, under the right strategy, these funds can later be rolled into a Roth IRA, where future withdrawals could be tax-free.

In simple terms:

1. You pay taxes now on contributions
2. Your earnings grow tax-deferred
3. You can roll into a Roth IRA for future tax-free growth

After-tax 401(k) is an advanced savings option that goes beyond the standard limits, and is especially useful for high earners or small business owners seeking more flexibility and tax-planning tools.

Who is a Good Candidate for After-Tax 401(k) Contributions?

Post-tax 401(k) contributions make the most sense when you’ve already maxed out your traditional or Roth 401(k) limits and are still looking for ways to stash away more for retirement.

You may be a strong candidate if:

• You are a High-Income Earner: If you consistently hit the IRS limit on traditional 401(k) contributions, after-tax contributions let you save even more in a tax-advantaged account.
• You Own a Business or Have Flexible Compensation: Small business owners or entrepreneurs can use this strategy to build wealth while offering attractive retirement plans to employees.
• You are Pursuing a Mega Backdoor Roth Strategy: After-tax 401(k) contributions can be rolled over into a Roth IRA, allowing tax-free growth on potentially large sums. This is not possible with direct Roth contributions due to income limits.
• You are Ineligible for Direct Roth IRA Contributions: If your income is too high to contribute directly to a Roth IRA, this is one way to still take advantage of tax-free growth through conversions.
• You Have a Long Investment Time Horizon: The longer your money stays invested, the more you benefit from compounding gains, especially if you plan to convert to a Roth IRA later and enjoy tax-free withdrawals.

How Do After-Tax 401(k) Contributions Work?

If you are enrolled in a traditional 401(k) through your employer, you likely make contributions directly from your paycheck. For the year 2025, the IRS allows employees under 50 to contribute up to $23,500.

If you are 50 or older, that limit rises to $31,000, and for those between the ages of 60 to 63, the contribution cap increases further to $34,750, thanks to additional catch-up contributions. On top of that, many employers offer matching contributions, usually a certain percentage of your salary.

Now, here’s where after-tax contributions come into play. The total combined limit for all contributions, including what you put in, your employer match, and any after-tax dollars, is $70,000 for 2025. If you are eligible for catch-up contributions, your cap could be $77,500 or even $81,250, depending on your age group.

So, if your regular pre-tax contributions and employer match don’t reach the full IRS cap, you may be able to continue contributing, this time using after-tax dollars, until you hit the annual limit. This strategy can help maximize your retirement savings.

Keep in mind, not all employers offer after-tax contribution options within their 401(k) plans. According to Vanguard’s How America Saves 2024 report, only 22% of Vanguard-managed 401(k) plans included this feature as of 2023.

So, it’s important to check with your HR or plan administrator to see whether your plan supports this additional savings opportunity.

What are Strategies for After-Tax 401(k) Contributions?

Check out these strategies that help high earners and savvy savers take full advantage of tax-advantaged retirement accounts, far beyond the base contribution limits.

1. Boost Overall Contributions

   After maxing out your pre-tax or Roth contributions, you can continue saving by adding after-tax money, if your employer’s plan permits. This allows you to increase your retirement savings beyond the standard contribution limit.

2. Convert to a Roth Account (In‑Plan or IRA)

   A powerful approach is to convert your after-tax contributions into a Roth account. You have two primary choices:

   • In-plan Roth conversion: Some 401(k) plans automatically convert after-tax contributions to Roth within the plan.
   • Rollover to Roth IRA: If in-plan conversion isn’t available, you can roll the funds into a Roth IRA. In both scenarios, contributions remain tax-free (since taxes are already paid), but earnings may be taxable upon conversion.

3. Split Contributions to Minimize Taxes

   To reduce tax exposure on earnings, you could direct the after-tax principal into a Roth account, where qualifying withdrawals are tax-free, while rolling the earnings into a traditional IRA, thus deferring taxes until withdrawal.

4. Leverage the “Mega Backdoor Roth”

   If your plan allows both after-tax contributions and Roth conversions, you can implement the mega backdoor Roth strategy. This tactic lets you effectively funnel more into Roth savings, potentially up to the total 401(k) limit for the year for future tax-free growth and withdrawals.

What are the Advantages of After-Tax 401 (k) Contributions?

Contributing after-tax dollars to your 401(k) gives you a chance to invest more money beyond standard limits and enjoy the benefit of tax-deferred growth. But it doesn’t stop there. You may also have the option to convert those contributions into a Roth account later on, allowing for tax-free growth and withdrawals in retirement.

Here are some more reasons why high earners and small business owners might adore this feature:

• Straight Paycheque Deductions

  Like other 401(k) contributions, after-tax contributions are simple to make and are deducted directly from your paycheque.

• Income Tax-Exempt Earnings (After Roth Rollover)

  All future profits can be withdrawn tax-free once they have been rolled into a Roth IRA, provided that all IRS requirements are satisfied.

• A Higher Contribution

  You can achieve the maximum $69,000 (or $76,500) 401(k) limit with after-tax contributions. It is a substantial amount higher than the typical $23,000 limitation.

• Adjustable Retractions

  Generally speaking, after-tax money can be taken out independently of pre-tax or Roth money, giving you more discretion when you need it.

• Portability

  You can maintain tax benefits by rolling over after-tax money into a regular or Roth IRA when you retire or change employment.

• Option to Rollover to a Roth IRA

  The “mega backdoor Roth” technique is smooth and effective because many plans allow in-plan Roth conversions.

• No Income Restrictions

  If your income is high, you can enjoy Roth-like benefits because after-tax contributions have no income cap, unlike Roth IRAs.

What are the Drawbacks of Post-Tax 401(K) Contributions?

While after-tax 401(k) contributions can be a valuable savings tool, they aren’t without downsides. Unlike Roth 401(k) contributions, the earnings from after-tax contributions are still taxable when withdrawn. Although 401(k) and 403(b) plans can offer this option, many don’t.

• Few Choices

  Not every 401(k) plan permits contributions made after taxes. Employers must collaborate with a supplier that provides these capabilities, such as Self-Directed Retirement Plans.

• The Intricate Rollover Procedure

  If done incorrectly, rolling over after-tax money to a Roth IRA can be challenging. Errors may result in needless taxes.

• Taxable Earnings

  Earnings on after-tax dollars are taxable unless they are promptly rolled into a Roth IRA, but contributions are not taxed again.

Should You Make After-Tax 401(k) Contributions?

After-tax contributions are a powerful strategy, only if used wisely. You can benefit most if:

• You’ve maxed out traditional and Roth contributions
• You want to increase tax-deferred or tax-free savings
• You have access to in-plan Roth conversions or know how to roll over correctly
• You are a high earner or business owner with tax-planning goals

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