Roth 401(k) vs. After-Tax 401(k) Contributions

Contributions to Roth 401(k) accounts and after-tax contributions to regular 401(k) accounts both involve after-tax dollars, but they follow different tax and distribution rules. Roth 401(k) contributions grow tax-free and allow tax-free withdrawals of both contributions and earnings in retirement if conditions are met. After-tax 401(k) contributions, by contrast, may be withdrawn tax-free but earnings are taxable. After-tax 401(k) accounts are often used to enable a mega backdoor Roth conversion.

A Roth 401(k) is a designated account within an employer-sponsored plan where contributions are made with after-tax dollars. Once inside the account, both contributions and investment earnings grow tax-free.

If the account holder is at least 59 ½ and the account has been open for five years, withdrawals are entirely tax-free, including any gains. This structure mirrors a Roth IRA but allows for higher annual contribution limits and access to employer matches, which are placed in a separate pre-tax account.

An after-tax 401(k) contribution, by contrast, is a non-deductible addition made to a non-Roth traditional 401(k) after the contribution limit for regular 401(k) accounts has been reached. Unlike Roth contributions, earnings on after-tax contributions are taxable upon withdrawal.

However, after-tax 401(k) contributions can be rolled over into a Roth IRA through a mega backdoor Roth strategy. Then the future growth will be tax-free. Without such a conversion, the tax treatment of gains makes after-tax 401(k) contributions less favorable for long-term growth.

While both options involve after-tax dollars, the long-term tax outcomes and strategic uses differ significantly between the two.

A Roth 401(k) lets you contribute post-tax dollars to your employer-sponsored plan. In 2025, the IRS set the employee contribution limit at $23,500 for individuals under 50. Those aged 50–59 and 64+ can add a $7,500 catch-up contribution, while employees aged 60–63 may contribute an enhanced catch-up of $11,250 if their plan allows. Combined employee and employer contributions cannot exceed $70,000 in 2025.

Withdrawals from a Roth 401(k) are tax-free if you’re over 59 ½ and have held the account for at least five years. Unlike Roth IRAs, Roth 401(k)s have no income-based eligibility requirements, making them accessible even for high earners.

Imagine you contribute $10,000 to a Roth 401(k). Since you’ve already paid income tax on that money, it goes into the account post-tax. Over time, your investments grow, and by retirement, your account is worth $25,000. As long as you’re at least 59 ½ and have held the account for five years, you can withdraw the full $25,000—both your original contribution and the $15,000 in gains—without owing any additional tax.

After-tax 401(k) contributions are made with money that’s already been taxed, similar to Roth contributions, but they’re treated differently when it comes to growth and withdrawals. These contributions begin only after you’ve maxed out your regular employee deferrals—$23,500 in 2025, or more with catch-up contributions if eligible. Total contributions, including employee, employer and after-tax, are capped at $70,000 in 2025.

Earnings on after-tax 401(k) contributions are taxable upon withdrawal unless the funds are rolled into a Roth account. This is the mega backdoor Roth strategy, where after-tax funds are quickly converted to a Roth account to secure tax-free growth.

Unlike Roth contributions, after-tax contributions aren’t subject to income limits or Roth-specific withdrawal rules, but they must follow general 401(k) withdrawal rules. Plans must allow after-tax contributions for this strategy to be available, and not all employers offer it. For those with high income or aggressive savings goals, after-tax contributions can provide a way to increase retirement plan deposits beyond standard limits.

Now consider an after-tax 401(k) contribution. Suppose you’ve already maxed out your regular 401(k) contributions and decide to contribute an extra $10,000 in after-tax dollars. That money goes in post-tax, but the earnings on it will be taxable when withdrawn.

If your account grows to $25,000, you’ll pay ordinary income tax when you withdraw the $15,000 in earnings. However, if you roll the after-tax portion into a Roth IRA soon after contributing using a mega backdoor Roth strategy, you can convert future gains into tax-free income. This assumes the transacting conforms to the Roth rules. The timing and handling of these funds transfers significantly affect their eventual tax impact.

Anyone eligible to participate in a 401(k) plan can make Roth 401(k) contributions, regardless of income. This makes Roth 401(k)s distinct from Roth IRAs, which phase out at higher income levels. However, not all plans offer a Roth contribution option—availability depends on the employer’s plan design.

After-tax 401(k) contributions are less common and only available in plans that explicitly allow them. And even if the plan allows after-tax 401(k) contributions, you must first max out standard employee contributions before you can contribute in the after-tax category.

Unlike Roth IRA contributions, after-tax contributions aren’t limited by income or age and there’s no catch-up contribution rule. As a result, these contributions are often used by high earners looking to go beyond annual deferral limits.

Choosing between Roth and after-tax 401(k) contributions depends on how you want your money to be taxed later and what your plan allows. Each serves a different purpose: one focuses on tax-free withdrawals, while the other can help boost savings beyond standard limits. After-tax 401(k) contributions are more potent when paired with a conversion strategy. Reviewing your plan’s features and understanding how each type of contribution works can help you take better advantage of what’s available.

• A financial advisor can help you determine when is the best time retire and manage other factors to maximize your benefits. Finding a financial advisor doesn’t have to be hard. SmartAsset’s free tool matches you with vetted financial advisors who serve your area, and you can have a free introductory call with your advisor matches to decide which one you feel is right for you. If you’re ready to find an advisor who can help you achieve your financial goals, get started now.
• SmartAsset’s Social Security calculator can help you estimate future monthly government benefits.

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