401k Calculator & Guide
After-tax 401(k) contributions can allow some participants to put additional money into a workplace retirement plan beyond regular employee elective deferrals. Learn how after-tax contributions work, how they differ from Roth 401(k) contributions and how the 2026 limits fit together.
An after-tax 401(k) contribution is an employee contribution made from compensation that is already included in income. It is different from both a traditional pre-tax deferral and a designated Roth 401(k) contribution.
The employee includes the contribution in income rather than excluding it through a traditional pre-tax salary deferral.
A non-Roth after-tax contribution is not the same as a designated Roth contribution. The tax treatment of the contribution and its future earnings differs.
After-tax employee contributions are plan-dependent. Not every 401(k) plan offers this feature.
The words "after-tax" are often used loosely, but IRS rules distinguish non-Roth after-tax contributions from designated Roth contributions.
| Feature | Traditional 401(k) | Roth 401(k) | After-tax 401(k) |
|---|---|---|---|
| Contribution tax treatment | Generally pre-tax | After-tax | After-tax |
| Included in income when contributed? | Generally no | Yes | Yes |
| Separate Roth account? | No | Yes | No |
| Subject to regular elective-deferral limit? | Yes | Yes | Generally no — subject to the overall plan limit |
| Earnings tax treatment | Generally taxable when distributed | Qualified distributions generally tax-free | Earnings generally remain pre-tax |
| Income limit for contribution? | No general income limit | No income limit for Roth 401(k) | No general income limit |
The exact availability and treatment of after-tax contributions depends on the plan document and applicable tax rules.
Understanding the source of the contribution is essential before calculating how much can go into the plan.
A traditional elective deferral generally reduces current federal taxable income, subject to the applicable rules. The 2026 employee elective-deferral limit is $24,500.
A Roth 401(k) contribution is included in income when made. Qualified distributions from the designated Roth account can generally be tax-free.
This contribution is made after tax but is not a designated Roth contribution. Its treatment under the overall plan contribution rules is different.
The amount of potential after-tax contribution room depends on the overall annual-additions limit and the other contributions going into your plan.
The 2026 basic employee elective-deferral limit for traditional and designated Roth 401(k) deferrals.
General 2026 defined-contribution annual-additions limit before applicable catch-up contributions.
2026 compensation limit generally used for applicable contribution calculations.
The regular $24,500 employee elective-deferral limit is not the same as the $72,000 overall annual-additions limit. Depending on the plan and your other contributions, the difference can potentially provide room for additional after-tax employee contributions. Catch-up contributions are handled separately under the applicable rules.
A simplified illustration can help show why employer contributions matter.
For 2026, the general defined-contribution annual-additions limit is $72,000 before applicable catch-up contributions.
Traditional and Roth elective deferrals count toward the applicable annual-additions calculation.
Matching and nonelective employer contributions can use part of the overall annual-additions capacity.
If the plan permits after-tax contributions, remaining annual-additions capacity can potentially be used for them.
Enter your employee deferral and employer contributions to estimate unused annual-additions capacity. This is a simplified educational calculation and does not determine your actual plan limit.
The calculator starts with the 2026 $72,000 annual-additions limit and subtracts the amounts entered below.
Estimated unused annual-additions capacity before considering plan-specific rules.
One of the most important reasons to distinguish non-Roth after-tax contributions from Roth 401(k) contributions is the treatment of future investment earnings.
The contribution itself has already been included in income. However, investment earnings associated with the after-tax contribution generally remain taxable amounts when distributed, subject to the applicable retirement-plan rules.
A designated Roth contribution is also included in income when contributed, but it is held in a separate designated Roth account. Qualified distributions, including qualifying earnings, can generally be excluded from gross income.
Some plans allow after-tax contributions to be converted or rolled into a Roth account. This is commonly discussed as the "mega backdoor Roth" strategy.
A plan may permit an employee to make non-Roth after-tax contributions beyond regular elective deferrals and then move those amounts into a Roth account through an eligible in-plan Roth rollover or another permitted rollover route.
Not every 401(k) offers the combination of features needed for this strategy. Before describing a plan as supporting a mega backdoor Roth, check its actual after-tax contribution, in-plan conversion and distribution provisions.
After-tax contributions are simply one component. The conversion or rollover features of the specific plan determine whether an after-tax-to-Roth strategy is available.
After-tax and pre-tax amounts can have different tax treatment during a distribution or rollover.
Your after-tax contribution represents money that has already been included in income. The basis can receive different treatment from the associated investment earnings.
Earnings associated with after-tax contributions are generally treated as pre-tax amounts and can create taxable consequences if distributed rather than properly rolled over.
IRS guidance allows certain distributions to be split between destinations, such as moving pre-tax amounts to a traditional IRA and after-tax amounts to a Roth IRA, when the applicable requirements are satisfied.
The IRS provides specific rules for distributions containing both pre-tax and after-tax amounts. Before executing a rollover, verify the transaction with the plan administrator and tax professional because the treatment can depend on the exact account composition and transaction structure.
The most important starting point is whether the employer's plan actually permits this type of contribution.
The plan document must provide the applicable contribution feature.
Contributions are made from compensation under the plan's applicable payroll rules.
Employee and employer contributions must remain within the applicable federal and plan limits.
Your benefits portal or Summary Plan Description should provide much of the information you need.
This is the first requirement. Many plans do not offer non-Roth after-tax employee contributions.
Check the plan's payroll and annual contribution rules, not only the federal maximum.
This feature can be important for participants considering an after-tax-to-Roth strategy.
Some plans provide distribution options while you are still employed; the terms vary by plan.
Understanding the separation between after-tax basis and associated earnings is important for future distributions.
Employer matching generally follows the plan's formula and can be based on eligible employee contributions.
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