What Are After-Tax 401(k) Contributions?
After-tax 401(k) contributions are a separate contribution source, not the same thing as Roth, that lets you save above the $24,500 deferral limit for 2026, up to the $72,000 all-sources 415(c) limit. Contributions come back tax-free, but earnings grow tax-deferred and are taxed at withdrawal. Their main modern use is the mega backdoor Roth.
On this page
After-tax (non-Roth) contributions do not count against the $24,500 elective deferral limit (IRC §402(g)). They do count against the $72,000 total annual additions limit (IRC §415(c)), shared with your deferrals and all employer money.
Source: IRC §402(g), §415(c); IRS Notice 2025-67
After-tax vs. Roth: they are not the same thing
If you have been using “after-tax” and “Roth” interchangeably, you are in very good company, and the confusion is understandable. Both go in with dollars you have already paid tax on. That is where the resemblance ends.
A Roth deferral is an elective deferral, which means it counts toward the $24,500 limit for 2026, and its earnings come out completely tax-free in a qualified withdrawal. An after-tax (non-Roth) contribution is a different source entirely. It sits outside the deferral limit, and its earnings grow only tax-deferred, so you owe ordinary income tax on those earnings when you take them out.
| Roth deferral | After-tax (non-Roth) | |
|---|---|---|
| Counts toward $24,500 (402(g))? | Yes | No |
| Counts toward $72,000 (415(c))? | Yes | Yes |
| Contributions taxed going in | Yes | Yes |
| Earnings at withdrawal | Tax-free if qualified | Taxable (tax-deferred growth) |
| Main use | Tax-free retirement income | Mega backdoor Roth conversions |
The practical takeaway is that after-tax money is only as good as your ability to convert it to Roth. That is the whole reason the rest of this page exists.
How much can I contribute after-tax in 2026?
There is no separate dollar limit for after-tax contributions, which is what makes them powerful. The ceiling is simply whatever room is left under the $72,000 415(c) limit for 2026 once your own deferrals and your employer’s contributions have taken their share.
Here is the arithmetic. Defer the full $24,500, receive $10,000 in employer match and profit sharing, and up to $37,500 of after-tax room remains, because $72,000 − $24,500 − $10,000 = $37,500. Catch-up contributions sit outside this math entirely and do not eat into the space.
One caution before you get excited about the number. Your plan is allowed to impose its own lower cap, often stated as a percentage of pay, and your plan document controls over the IRS ceiling.
How much after-tax room do I have?
| 2026 total annual additions limit (IRC §415(c)) | $72,000 |
| Minus your own pre-tax and Roth deferrals for the year | −$_______ |
| Minus everything your employer contributes (match plus profit sharing) | −$_______ |
| Your after-tax contribution space | $_______ |
A worked example. You defer the full $24,500 and your employer contributes $7,000 in match. Your after-tax room is $72,000 − $24,500 − $7,000, which comes to $40,500. Two notes on filling this in. Use your employer’s full-year expected contribution, not what has been deposited so far, or you will over-shoot and trigger a correction. And do not subtract catch-up contributions, because they sit on top of the $72,000 rather than inside it. Whatever number you land on, check it against any percentage-of-pay cap your own plan applies.
The mega backdoor Roth strategy
Standing on their own, after-tax contributions are a middling deal. You pay tax on the money going in and pay tax on the earnings coming out, which is the weaker half of each world.
The reason high savers care about them today is that the money can be converted into Roth money through what is known as the mega backdoor Roth. The mechanic has three steps.
- Max your regular deferrals, which is $24,500 for 2026, in either pre-tax or Roth form.
- Contribute after-tax dollars up to whatever 415(c) room you have left.
- Move the after-tax money to Roth quickly, by one of two routes. The first is an in-plan Roth conversion, which many plans automate as a “daily convert” feature. The second is a rollover out of the plan. Under IRS Notice 2014-54, a distribution of your after-tax account can be split so that the basis goes to a Roth IRA and the earnings go to a traditional IRA, with no tax due on the move.
Converted promptly, the after-tax basis turns into Roth money whose future growth is tax-free, and at a scale far beyond the $7,500 IRA limit for 2026. Speed is the thing to get right. Any earnings that pile up between the contribution and the conversion are taxable at conversion, which is why an automatic in-plan conversion every payroll is the cleanest possible setup.
| Your elective deferrals (402(g) max) | $24,500 |
| Employer match (4% of pay) | $6,000 |
| 415(c) limit for 2026 | $72,000 |
| After-tax room available | $41,500 |
Does my plan allow after-tax contributions?
Only a minority of plans offer an after-tax contribution source, and fewer still pair it with in-plan conversion. This is a plan-design choice your employer made, not a right you can insist on, so the first job is simply finding out what you have. Three ways to check.
- Search your summary plan description for “after-tax,” “voluntary contributions,” or “employee after-tax.”
- Look at your contribution election screen. If your recordkeeper (Fidelity, Empower, Vanguard, and the rest) shows a third election beyond pre-tax and Roth, that third one is it.
- Ask the administrator two specific questions. “Does the plan accept after-tax (non-Roth) contributions?” and “Does it allow in-plan Roth conversion or in-service distribution of the after-tax account?” You need a yes to the first for the contributions and a yes to the second for the mega backdoor to work at all.
Tax treatment at withdrawal
Your contributions, known as your basis, come back to you tax-free, since you already paid tax on that money once. The earnings are taxable as ordinary income.
What surprises people is that you cannot simply withdraw the basis and leave the earnings behind. Under IRC §72(e)(8), any distribution from the after-tax account comes out pro-rata between basis and earnings, meaning every withdrawal is part tax-free and part taxable in the same ratio as the account itself. Contributions made before 1987, if your plan tracked them separately, are grandfathered and can come out basis-first.
If you are under 59½, the 10% early-withdrawal penalty applies only to the taxable earnings portion, not to your basis. The full treatment with worked math is on withdrawing after-tax 401(k) money.
ACP testing limits for high earners
After-tax contributions get counted in the ACP nondiscrimination test alongside matching contributions, and safe harbor status does not exempt them. That test compares what higher-paid employees put in against what everyone else puts in.
If highly compensated employees contribute heavily after-tax while other employees contribute little, the plan can fail the test and has to refund contributions to those HCEs. This is why some plans cap after-tax contributions for HCEs in the first place, and why a large after-tax election can come back to you as a taxable corrective refund the following spring.
If that refund lands in your mailbox, it is the plan’s testing math at work rather than an error on your part. Nothing was done wrong, and nothing is owed beyond the tax on the returned amount.
Value without the Roth conversion
Is after-tax money worth contributing if you cannot convert it? In most cases only after better options are exhausted. Unconverted after-tax money pairs taxed contributions with taxable earnings, which really is the weakest of both worlds, though it still grows tax-deferred and adds some tax diversification to your retirement savings.
For most people the priority order runs like this. Capture the full employer match first. Max the $24,500 in pre-tax or Roth deferrals second. Fund an IRA third. Only then turn to after-tax contributions, and ideally only with a conversion route already in place.
Should I make after-tax contributions?
- If you are not yet capturing the full employer match → Stop here and raise your regular deferral first. Nothing on this page beats free match money.
- If you have not maxed the $24,500 deferral limit → Fill that first, especially in Roth form. A Roth deferral gives you tax-free earnings with no conversion step and no plan features required.
- If you are maxed out and your plan offers both after-tax contributions and in-plan Roth conversion → This is the ideal case. Contribute up to your remaining 415(c) room and set the conversion to happen automatically each payroll.
- If your plan offers after-tax contributions but no conversion route → Fund a taxable brokerage account or an IRA instead. Unconverted after-tax money accumulates earnings you will be taxed on later at ordinary income rates.
- If you are a highly compensated employee and your plan is not safe harbor → Ask about ACP testing history before you commit a large amount, since you may get part of it refunded next spring.
- If your cash flow is uncertain this year → Skip it. After-tax contributions come from money you have already been taxed on, so they cost real take-home pay and belong at the end of the list, not the start.
Frequently asked questions
What is the after-tax 401(k) contribution limit for 2026?
There is no standalone after-tax limit. After-tax contributions fill the space between your deferrals plus employer contributions and the $72,000 415(c) ceiling for 2026. In theory that leaves up to $47,500 for someone deferring $24,500 with no employer money at all, and less in practice as employer contributions use up the room.
Is post-tax 401(k) the same as Roth?
People use “post-tax” loosely for both, but in plan terms the answer is no. Roth deferrals count toward the $24,500 limit for 2026 and earn tax-free growth. After-tax (non-Roth) contributions sit above that limit and their earnings are merely tax-deferred. Check which source your election screen actually names, because the label on the screen is what your payroll system will follow.
Do after-tax contributions reduce my taxable income?
No. They come out of pay that has already been taxed, so there is no deduction and no reduction in your W-2 wages. The tax benefit is deferred growth on the earnings, or tax-free growth if you convert the money to Roth.
How fast should I convert after-tax money to Roth?
As fast as your plan allows, and ideally automatically with each payroll. Earnings that accrue between the contribution and the conversion are taxable at conversion, so a long gap creates a tax bill that prompt conversion avoids entirely.
Can I roll after-tax 401(k) money into a Roth IRA?
Yes, once you are eligible for a distribution. Under IRS Notice 2014-54 you can direct the basis to a Roth IRA and the earnings to a traditional IRA in one split rollover, and you owe no tax on the move itself.
Why would my plan refund my after-tax contributions?
The most likely reason is a failed ACP test. After-tax contributions by highly compensated employees are tested against what everyone else contributes, and a failing plan has to return the excess to those HCEs as a taxable corrective distribution.
Related reading
- Withdrawing after-tax 401(k) money: the pro-rata rule with worked examples
- The 415(c) limit: the $72,000 all-sources cap for 2026
- Roth 401(k): the other way to get tax-free retirement money
Sources: IRS Notice 2014-54 · IRS Notice 2025-67 (2026 limits) · IRC §72(e)(8) · IRS: rollovers of after-tax contributions