An after-tax contribution is money you put into a retirement account from income you’ve already paid taxes on, so the principal comes back out tax-free. The earnings on that principal, however, are usually taxed as ordinary income when you withdraw them, unless the money sits in a Roth account or gets converted into one. In a 401(k), after-tax dollars can be layered on top of your regular deferrals and employer match, up to the 2026 defined contribution ceiling of $72,000.1Internal Revenue Service. 2026 Amounts Relating to Retirement Plans and IRAs, as Adjusted for Changes in Cost-of-Living
The Three Tax Buckets
Every dollar in a retirement account sits in one of three tax buckets: pre-tax, Roth, or after-tax. Pre-tax contributions reduce your taxable income now and get taxed on withdrawal. Roth contributions use money you’ve already paid taxes on, and qualified withdrawals (including earnings) come out tax-free. After-tax contributions also use post-tax dollars, but the earnings grow tax-deferred and are taxed as ordinary income when you take them out.
This is where people get tangled up. Roth and after-tax are both funded with dollars you’ve already paid income tax on, so they sound identical. The difference lives in the earnings: Roth earnings are tax-free at qualified distribution, after-tax earnings are taxable. In workplace plan language, “after-tax contributions” almost always means the non-Roth after-tax sub-account inside a 401(k) or 403(b), a separate bucket that sits next to your pre-tax and Roth buckets. Not every plan offers it. Check your plan’s summary plan description before assuming you have access.
Where After-Tax Money Can Go
Four account types accept after-tax dollars, and the rules differ enough that they aren’t interchangeable.
Roth IRA
A Roth IRA is funded entirely with after-tax dollars, and those contributions can never be deducted.2Internal Revenue Service. Roth IRAs The 2026 limit is $7,500 if you’re under 50 and $8,600 if you’re 50 or older.3Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500 Income eligibility is the catch. For 2026, single filers with modified adjusted gross income above $168,000 and married joint filers above $252,000 cannot contribute directly. Contributions phase out starting at $153,000 (single) and $242,000 (joint).1Internal Revenue Service. 2026 Amounts Relating to Retirement Plans and IRAs, as Adjusted for Changes in Cost-of-Living
Designated Roth 401(k)
Contributions come from after-tax income, and qualified withdrawals are tax-free. The 2026 elective deferral limit is $24,500, shared between your pre-tax and Roth 401(k) contributions combined.3Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500 Unlike Roth IRAs, Roth 401(k)s have no income limits.4Internal Revenue Service. Roth Comparison Chart
Non-Roth After-Tax 401(k)
This is the bucket most people mean when they say “after-tax contributions.” Some employer plans let you contribute additional after-tax dollars above the $24,500 elective deferral limit, up to the overall defined contribution cap of $72,000 for 2026.1Internal Revenue Service. 2026 Amounts Relating to Retirement Plans and IRAs, as Adjusted for Changes in Cost-of-Living The earnings grow tax-deferred, not tax-free, so most people don’t leave money here long-term. Its value is as a stepping stone to a Roth account.
Non-Deductible Traditional IRA
If your income is too high to deduct a traditional IRA contribution, or a workplace plan limits your deductibility, you can still contribute on a non-deductible basis. Those are after-tax dollars sitting in a traditional IRA. The 2026 IRA limit of $7,500 ($8,600 if 50 or older) applies across all your traditional and Roth IRAs combined.3Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500 Earnings grow tax-deferred and are taxed on withdrawal. Tracking your basis matters here, which is why the IRS requires Form 8606.
2026 Limits and Your After-Tax Room
The numbers for 2026:
- Elective deferral limit (pre-tax and Roth combined): $24,5003Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026, IRA Limit Increases to $7,500
- Catch-up for ages 50–59 and 64+: an additional $8,000
- SECURE 2.0 super catch-up for ages 60–63: $11,250 instead of $8,000
- Total defined contribution limit under Section 415(c): $72,000, covering employee deferrals, employer contributions, and after-tax dollars combined1Internal Revenue Service. 2026 Amounts Relating to Retirement Plans and IRAs, as Adjusted for Changes in Cost-of-Living
- IRA limit: $7,500, or $8,600 if 50 or older
One detail catches people: catch-up contributions under IRC 414(v) do not count against the $72,000 Section 415(c) cap.5Internal Revenue Service. Failure to Limit Contributions for a Participant A 55-year-old can hit $72,000 in annual additions and still add $8,000 in catch-up deferrals on top.
Your after-tax contribution room in a 401(k) is what’s left after your deferrals and employer contributions. Take the $72,000 cap, subtract your elective deferrals, subtract your employer’s match and any nonelective contributions. What remains is the after-tax space. Defer $24,500 with a $12,000 employer match, and $35,500 of after-tax room is open.
The Mega Backdoor Roth
The non-Roth after-tax bucket exists in most financial plans for one reason: the mega backdoor Roth. You contribute after-tax dollars into that bucket, then convert or roll them into a Roth account where future earnings grow tax-free. It moves far more money into Roth treatment than the $24,500 deferral limit or the $7,500 IRA limit allow on their own.
Two plan features have to be in place. Your 401(k) must permit after-tax contributions, and it must offer either in-plan Roth conversions or in-service withdrawals to a Roth IRA. Without one of those, you’ll have to wait until you leave the employer to move the money. Ask your plan administrator directly.
The math: someone under 50 maxes out $24,500 in Roth 401(k) deferrals with $10,000 in employer match. The 415(c) cap of $72,000 leaves $37,500 of after-tax space. Contribute that $37,500 and convert it immediately, and you’ve moved $62,000 into Roth treatment in a single year.
Timing matters. The longer after-tax dollars sit before conversion, the more taxable earnings accumulate inside the bucket. Those earnings are taxable at conversion. Fast conversions, ideally automatic in-plan conversions where the plan offers them, keep the taxable piece small.
How Withdrawals Are Taxed
What comes out depends on which account holds the money.
Qualified distributions from a Roth IRA or designated Roth 401(k) are entirely tax-free, earnings included. A distribution qualifies when you’ve held the account for at least five tax years and you’ve reached age 59½, become disabled, or died.6Internal Revenue Service. Retirement Plans FAQs on Designated Roth Accounts The five-year clock for a Roth 401(k) starts January 1 of the year of your first designated Roth contribution to that plan. For a Roth IRA, it starts January 1 of the year of your first contribution to any Roth IRA. Pull money before meeting both conditions and you’ll owe income tax on the earnings portion, plus a possible 10% early withdrawal penalty if you’re under 59½.7Internal Revenue Service. Traditional and Roth IRAs Your original Roth IRA contributions come out first and are always tax-free and penalty-free.
For the non-Roth after-tax bucket in a 401(k) or non-deductible contributions in a traditional IRA, only your original contributions come back tax-free. The earnings are taxed as ordinary income.8Internal Revenue Service. Retirement Topics – Designated Roth Account That taxable-earnings feature is why people move this money to Roth quickly.
The Pro-Rata Rule
If you hold a traditional IRA with both deductible and non-deductible contributions, you can’t pick which dollars come out during a distribution. The IRS pools all your traditional IRAs together and applies a proportional split between taxable and non-taxable amounts. If 20% of your combined traditional IRA balance is non-deductible basis and 80% is pre-tax money plus earnings, then 80% of any distribution or conversion is taxable.9Internal Revenue Service. Publication 590-A (2025), Contributions to Individual Retirement Arrangements (IRAs)
This is the reason non-deductible traditional IRA contributions get complicated, particularly for people attempting a backdoor Roth conversion. Existing pre-tax IRA money creates taxable income on any conversion, proportionally. The workaround, when available, is rolling pre-tax IRA balances into a 401(k) first to isolate the non-deductible basis before converting.
Workplace 401(k) plans work differently under IRS Notice 2014-54. When you take a distribution containing both pre-tax and after-tax money, you can direct the pre-tax portion to a traditional IRA and the after-tax portion to a Roth IRA as part of the same distribution.10Internal Revenue Service. Guidance on Allocation of After-Tax Amounts to Rollovers Notice 2014-54 The IRS treats simultaneous disbursements as a single distribution for allocation purposes, so you can cleanly separate basis from taxable earnings. That’s why the mega backdoor Roth works so much better from a 401(k) than from a traditional IRA.
Reporting: Form 8606 and Form 1099-R
If you make non-deductible contributions to a traditional IRA, file Form 8606 with your tax return for that year.11Internal Revenue Service. About Form 8606, Nondeductible IRAs It’s your running ledger of after-tax basis. When you later take distributions or convert to Roth, Form 8606 is the proof that certain dollars were already taxed. Skipping the form triggers a $50 penalty, but the bigger cost is losing your basis record and paying tax on the same money twice.12IRS.gov. 2024 Instructions for Form 8606
When you take a distribution from any retirement account, the financial institution issues Form 1099-R.13Internal Revenue Service. Instructions for Forms 1099-R and 5498 Watch Box 2b. If “taxable amount not determined” is checked, the institution isn’t calculating your taxable amount for you. You have to do it from your Form 8606 basis records.
Fixing Excess Contributions
Overshoot an IRA limit and the penalty is a 6% excise tax on the excess for each year it stays in the account.14Internal Revenue Service. IRA Excess Contributions Withdraw the excess plus any earnings on it before your tax filing deadline, including extensions, and the penalty goes away. Leave it in, and the 6% compounds annually.
Excess 401(k) elective deferrals follow a different fix. The excess plus allocable earnings must be distributed back by April 15 of the following year.15Internal Revenue Service. Consequences to a Participant Who Makes Excess Deferrals to a 401(k) Plan Hit the deadline and you avoid double taxation. Miss it, and the excess gets taxed in the year of contribution and again on eventual withdrawal. Plan administrators usually watch the 415(c) limit, but if you contribute to multiple employer plans in the same year, tracking the totals is on you.