Difference Between Roth and After-Tax 401(k) Contributions

The difference between Roth and after-tax 401(k) contributions comes down to what happens to your investment earnings. Both types come from money you’ve already paid income tax on, but Roth earnings grow tax-free and stay tax-free at withdrawal, while after-tax earnings grow tax-deferred and get taxed as ordinary income when you take them out. That single distinction shapes the contribution limits, withdrawal mechanics, required minimum distributions, and rollover options for each.

How Earnings Are Taxed

Inside a Roth 401(k), every dollar of growth belongs to you. Interest, dividends, and capital gains accumulate without any tax liability, and as long as your eventual withdrawal qualifies, the IRS never takes a cut. You pay tax once, on the way in, and that’s the end of it.¹

After-tax contributions behave differently in a way that surprises many savers. Your original contributions were already taxed, so you can eventually get that principal back without owing anything additional. But the earnings on those contributions sit in a separate taxable bucket. While the money stays in the plan, those earnings are tax-deferred, not tax-free. When you pull them out, the IRS taxes them at your ordinary income rate. The growth behaves like money in a traditional pre-tax 401(k), even though the starting contributions were already taxed.²

For someone decades from retirement, this distinction compounds heavily. A Roth balance that doubles or triples over 30 years owes nothing on that growth. An after-tax balance that does the same carries a growing embedded tax bill on every dollar of appreciation.

How Much You Can Contribute

Roth 401(k) contributions count against the same elective deferral limit that covers traditional pre-tax contributions. For 2026, that limit is $24,500. If you put $10,000 into pre-tax and $14,500 into Roth, you’ve hit the ceiling. The two share a single bucket under Internal Revenue Code Section 402(g).³

Workers age 50 and older can add an extra $8,000 in catch-up contributions for 2026, bringing their maximum elective deferrals to $32,500. Under a SECURE 2.0 provision that took effect in 2025, participants ages 60 through 63 get an even higher catch-up limit of $11,250, pushing their elective deferral ceiling to $35,750.³

After-tax contributions operate under a much larger cap. Section 415(c) sets a total annual addition limit of $72,000 for 2026. That limit covers everything going into your account: your elective deferrals (pre-tax and Roth), employer matching contributions, and your voluntary after-tax contributions. Catch-up contributions are excluded from this calculation entirely.⁴⁵

The practical math: if you defer $24,500 and your employer adds $12,000 in matching funds, you’ve used $36,500 of the $72,000 cap. That leaves $35,500 of room for after-tax contributions. High earners who want to save more than the elective deferral limit allows use this gap.

Rules for Taking the Money Out

Roth 401(k) Withdrawals

A completely tax-free withdrawal from your Roth 401(k) has to be “qualified.” That requires meeting two conditions: you must be at least 59½ years old (or disabled, or deceased with a beneficiary taking the distribution), and at least five taxable years must have passed since your first Roth contribution to that plan. The five-year clock starts on the first day of the tax year you made your initial Roth contribution.⁶⁷

If you take money out before meeting both conditions, you owe ordinary income tax on the earnings portion. Your original contributions come back tax-free either way since they were already taxed. The IRS calculates the taxable share by looking at the ratio of your total Roth contributions to the total account balance.⁶

One detail worth noting: if you roll a Roth 401(k) balance from a former employer’s plan into your current employer’s Roth 401(k), the five-year clock can carry over from the earlier plan. Switching jobs doesn’t necessarily reset your waiting period.⁶

After-Tax Withdrawals

After-tax withdrawals follow a less favorable set of rules built around pro-rata distribution. Every dollar you pull from your after-tax balance is treated as a proportional mix of your original (already-taxed) contributions and the taxable earnings they generated. You cannot cherry-pick just the non-taxable principal and leave the earnings behind.²

Say your after-tax account holds $50,000 in contributions and $10,000 in earnings. Roughly 83% of any distribution is tax-free return of principal and 17% is taxable earnings. This forced blending creates a tax hit on every partial withdrawal, which is why most advisors recommend converting after-tax money to Roth before it accumulates much growth.

Required Minimum Distributions

Until recently, Roth 401(k) accounts had a frustrating quirk: despite offering tax-free growth, they still required you to start taking distributions in retirement, just like a traditional 401(k). SECURE 2.0 eliminated that requirement. Starting with taxable years beginning after December 31, 2023, designated Roth accounts in 401(k) and 403(b) plans are no longer subject to required minimum distributions during the account owner’s lifetime.⁸

After-tax contributions don’t get this treatment. They remain part of the overall plan balance and are subject to the same RMD schedule as any other non-Roth money in the plan. A Roth 401(k) balance can sit untouched for your entire lifetime; an after-tax balance forces distributions on a schedule you may not want.

Moving Money Out of the Plan

Roth 401(k) money rolls cleanly into a Roth IRA. Since both accounts hold after-tax contributions with tax-free earnings, there’s no tax event on the rollover. Once inside a Roth IRA, the money picks up that account’s more flexible withdrawal rules, and if the Roth IRA already has its own five-year clock running, the transferred funds benefit immediately.

After-tax money requires more careful handling. Under IRS Notice 2014-54, when you take a distribution that includes both after-tax contributions and their associated earnings, you can split the money across two destinations in a single transaction. Your after-tax principal goes to a Roth IRA tax-free, and the earnings go to a traditional IRA, where they remain tax-deferred until you eventually withdraw them. That split prevents you from owing income tax on the earnings at the time of rollover.²

There’s a catch. You cannot roll over only your after-tax contributions while leaving everything else in the plan. Any partial distribution must include a proportional share of pre-tax amounts. If your plan allows source-specific withdrawals, you may be able to take just the after-tax source balance and split it between a Roth IRA and a traditional IRA. Not every plan offers that flexibility.²

The Mega Backdoor Roth

The gap between the elective deferral limit ($24,500) and the total annual addition limit ($72,000) is where after-tax contributions become strategically valuable. By making after-tax contributions to fill that gap and then immediately converting them to Roth, you can move far more money into tax-free growth than the standard Roth contribution limit would allow. This approach is commonly called the “Mega Backdoor Roth.”

The mechanics rely on IRS Notice 2014-54, which lets you direct after-tax principal into a Roth IRA or Roth 401(k) while routing any accumulated earnings to a traditional IRA.⁹ The key is converting quickly. If your plan supports automatic in-plan Roth conversions that happen right after each paycheck contribution, there’s almost no time for earnings to accumulate, so the entire converted amount enters the Roth bucket with zero tax consequences. If you wait months or years, the earnings that built up become taxable income in the year of conversion.

Not every plan supports this strategy. Your plan has to allow after-tax contributions, permit in-service distributions or in-plan Roth conversions, and ideally process those conversions automatically. If any of those features are missing, the Mega Backdoor Roth isn’t available regardless of how much 415(c) room you have.

Which One to Use

If your plan offers both and you haven’t maxed out the elective deferral limit, Roth contributions are almost always the better choice over after-tax contributions. The tax-free growth, elimination of RMDs, and cleaner withdrawal rules make Roth the more powerful account. The one scenario where traditional after-tax contributions are clearly preferable is when you’ve already hit the $24,500 elective deferral cap and want to save more. At that point, after-tax contributions are the only way to push additional money into your employer plan, and if you can convert them to Roth quickly, the distinction between the two largely disappears.

The worst outcome is letting after-tax contributions sit unconverted for years. The earnings pile up in a taxable bucket, you’re stuck with pro-rata withdrawal rules, and you’ve gained only tax deferral on the growth rather than the tax-free treatment you could have had with a timely Roth conversion. If your plan doesn’t support in-plan conversions or in-service rollovers, think carefully about whether after-tax contributions are worth the complexity compared with a taxable brokerage account, where you’d at least benefit from long-term capital gains rates instead of ordinary income rates on the earnings.

Not every employer offers either feature. Roth 401(k) options have become common, but after-tax contribution provisions remain less widespread because they add administrative complexity for the plan sponsor. Check your summary plan description or ask HR before you build a strategy around a feature your plan may not have.

1
Internal Revenue Service. Retirement Topics – Designated Roth Account
2
Internal Revenue Service. Rollovers of After-Tax Contributions in Retirement Plans
3
Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026; IRA Limit Increases to $7,500
4
Internal Revenue Service. Fixing Common Plan Mistakes – Failure to Limit Contributions for a Participant
5
Internal Revenue Service. COLA Increases for Dollar Limitations on Benefits and Contributions
6
Internal Revenue Service. Retirement Plans FAQs on Designated Roth Accounts
7
Office of the Law Revision Counsel. 26 USC 402A – Optional Treatment of Elective Deferrals as Roth Contributions
8
Congress.gov. Required Minimum Distribution (RMD) Rules for Original Owners
9
Internal Revenue Service. Notice 2014-54