After-Tax 401(k) Contributions and the Mega Backdoor Roth for 2026

A mega backdoor Roth is a two-step move inside a 401(k): you make after-tax (non-Roth) contributions above the normal deferral limit, then move that money into Roth status, either by an in-plan Roth conversion or by an in-service withdrawal rolled to a Roth IRA. For 2026 the ceiling is the §415(c) annual additions limit of $72,000, minus your own deferrals and your employer's contributions.² It only works if your plan allows both steps, and many plans allow neither.

The 2026 numbers that set the room

Three limits interact. Your elective deferral (pre-tax plus Roth 401(k)) is capped per person. The annual additions limit is a separate, larger cap on everything that lands in your account in one plan for the year.

2026 limit	Amount	What it covers
Elective deferral, §402(g)	$24,500	Your pre-tax and Roth 401(k) contributions combined1
Catch-up, age 50 and over	$8,000	Extra deferral; does not count toward $72,0001
Catch-up, ages 60 to 63	$11,250	Replaces the $8,000 figure for those ages1
Annual additions, §415(c)	$72,000 or 100% of pay, whichever is less	Deferrals, employer match, employer nonelective contributions, forfeitures, and after-tax employee contributions34
IRA contribution	$7,500	Separate from the 401(k) entirely1

With catch-up added on top, the IRS puts the total at $80,000 for people 50 and over, or up to $83,250 for ages 60 to 63.³ Earnings, loan repayments and rollovers don't count as annual additions.⁴

Why bother at all? Direct Roth IRA contributions phase out for 2026 between $153,000 and $168,000 of modified AGI for single filers and between $242,000 and $252,000 for married couples filing jointly.¹ After-tax 401(k) money has no income test, so for higher earners it can be the largest Roth door available.

The §415(c) math, worked through

Example (hypothetical, 2026, employee under 50): salary $150,000. The plan matches 50% of the first 6% of pay.

Line	Amount
Annual additions limit (lesser of $72,000 or $150,000 of pay)	$72,000
Employee deferral, pre-tax or Roth	−$24,500
Employer match (50% × 6% × $150,000)	−$4,500
Room left for after-tax contributions	$43,000

That $43,000 is the legal maximum, not a promise. Two things usually cut it down.

The plan's own cap comes first. Many plans limit after-tax contributions to a percentage of pay. If the plan in this example caps them at 10%, the real figure is $15,000, and the §415(c) arithmetic stops mattering.

Cash flow comes second. In the same example, spreading $43,000 over 26 biweekly paychecks means $1,653.85 per check, on top of the deferral and taxes. Most households hit that wall long before the IRS limit.

Two variations change the picture:

• Age 50 to 59, or 64 and over: the $8,000 catch-up sits outside the $72,000, so after-tax room stays $43,000 and total contributions can reach $80,000.
• Lower pay: for example, at a $50,000 salary the §415(c) limit is $50,000, because 100% of pay is the smaller number. Deferral $24,500 plus a $1,500 match leaves $24,000 of after-tax room on paper, which would need nearly all the remaining paycheck. At this income level the mega backdoor is mostly theoretical.

A side note for catch-up savers: starting in 2026, if your prior-year wages from the employer sponsoring the plan exceeded $150,000, your catch-up contributions must go in as Roth.² The final regulations generally apply from 2027, and plans may follow a reasonable good-faith reading of the law before then.⁹ This rule affects catch-up deferrals, not the after-tax bucket, but it changes the tax mix of the same paycheck.

Plan features you need, and how to check

Ask HR or read the summary plan description for three items. Without the first and at least one of the other two, there's no mega backdoor.

1. After-tax employee contributions allowed. This is a separate source from Roth 401(k) deferrals. The IRS defines it as an after-tax contribution "other than a designated Roth contribution."⁴ Plan paperwork that only mentions "Roth" usually means Roth deferrals, which share the $24,500 limit.
2. In-plan Roth rollover (conversion) of after-tax amounts. Plans may let you move after-tax contributions into the plan's designated Roth account, and they can restrict which sources qualify and how often.⁶
3. In-service distribution of the after-tax subaccount. This lets you take the money out while still employed and roll it to a Roth IRA.

Plans aren't required to offer in-plan Roth rollovers at all.⁶ Some recordkeepers also offer an automatic conversion after every paycheck. When available, it's the feature that matters most, for the reason in the next section.

In-plan conversion vs. in-service withdrawal

Both routes end in Roth money. They differ in where it sits and how the earnings get taxed.

Dimension	In-plan Roth conversion	In-service withdrawal to Roth IRA
Where the money ends up	Designated Roth account in the same plan	Roth IRA at a provider you choose
Plan must allow	In-plan Roth rollover of after-tax money6	In-service distribution of after-tax money
Tax at conversion	Amount converted minus your after-tax basis, so in practice the earnings6	Same, unless earnings are sent to a traditional IRA under Notice 2014-547
Investment menu	The plan's funds	Whatever the IRA custodian offers
Withholding	No §3405 withholding on a direct in-plan rollover of otherwise nondistributable amounts10	Ask for a direct rollover and check the plan's withholding rules
Five-year clock for qualified Roth distributions	Runs from the first designated Roth contribution to that plan6	Governed by Roth IRA rules

Amounts converted in-plan that couldn't otherwise be distributed stay subject to the plan's original distribution restrictions.¹⁰ So the in-plan route doesn't make the money easier to reach. It changes only its tax character.

A practical rule: if the plan offers automatic in-plan conversion, it usually beats periodic withdrawals, because earnings never get time to build up untaxed in the after-tax subaccount. If the plan only allows withdrawals a few times a year, do them as often as the plan permits.

Earnings, pro-rata and Notice 2014-54

After-tax contributions are basis: you already paid income tax on them. The earnings on those contributions are pre-tax money.⁷ That split drives the tax bill.

Example (hypothetical): $43,000 goes into the after-tax subaccount during the year and is withdrawn once, in December, after it has earned $1,290. Under Notice 2014-54, a single distribution sent to several destinations is treated as one distribution, and pre-tax amounts are assigned first to the part that's directly rolled over to a pre-tax destination.⁸ So you can send the $43,000 of contributions to a Roth IRA and the $1,290 of earnings to a traditional IRA, owing no tax now. Or you can roll all $44,290 to a Roth IRA and report $1,290 as income.

What the notice doesn't do is let you pull only after-tax dollars out of a mixed account. A distribution generally carries a pro-rata share of pre-tax and after-tax amounts. The IRS example: a $100,000 account holding $80,000 pre-tax and $20,000 after-tax pays out $40,000 pre-tax and $10,000 after-tax on a $50,000 distribution.⁷ Whether a withdrawal draws on the after-tax subaccount alone or on the whole account depends on how the plan defines its sources. Get that in writing before the first request.

The rules in Notice 2014-54 apply to distributions made on or after September 18, 2014.⁷

Why many plans cap or refuse after-tax contributions

The usual reason is the actual contribution percentage (ACP) test. It checks whether matching contributions and employee after-tax contributions favor highly compensated employees over everyone else.⁴⁵ For 2026, the highly compensated employee threshold under §414(q) remains $160,000.²

After-tax contributions come mostly from higher earners, which pushes the HCE average up. The ACP safe harbor that safe harbor 401(k) plans use is tied to matching contributions, so it doesn't automatically clear a plan with heavy after-tax use.⁵ A plan that fails the test has to correct it, often by returning money to HCEs after year-end. Plans avoid that by capping after-tax contributions as a percentage of pay, limiting them for HCEs, or leaving the feature out.

The failure mode to plan for: you contribute $20,000 after-tax, the plan fails ACP, and part of it comes back as a refund months later. If you're likely to be an HCE, ask the plan how often after-tax contributions have been refunded.

Who this is not for

• Anyone who hasn't covered the basics. Deferral up to the full match, an emergency fund, and high-interest debt come first. See building a high savings rate for the order.
• People who need the money before 59½ without a plan for access. In-plan converted amounts keep the plan's withdrawal restrictions.¹⁰
• Workers whose plan has no conversion or in-service option. Leaving money in the after-tax subaccount for years means the earnings are taxed as ordinary income when they come out. That can end up worse than a regular taxable brokerage account.
• Self-employed people with no employees. The same §415(c) limit applies to a one-participant 401(k), but whether after-tax contributions are allowed depends on the plan document. The non-W2 income guide covers the Solo 401(k) and SEP limits.

Common mistakes

• Confusing Roth 401(k) deferrals with after-tax contributions. They are different sources with different limits.
• Forgetting the employer match when computing room. Overshooting the $72,000 forces a correction.
• Converting once a year. Twelve months of growth in the after-tax subaccount becomes taxable income at conversion.
• Assuming the deferral limit resets with a new job. The $24,500 is per person across employers; the $72,000 is per plan.³
• Ignoring the effect on taxable income in a year when other income matters, such as a year with marketplace health coverage. The early retirement health coverage guide explains how MAGI drives premiums.

FAQ

Does the mega backdoor Roth affect the $7,500 IRA limit?

No. IRA contributions and 401(k) after-tax contributions are separate limits. A Roth IRA can receive a rollover of after-tax 401(k) money in addition to the annual IRA contribution.

Can both spouses do it?

Each spouse uses their own plan and their own §415(c) limit, if each plan offers the features. A spouse whose plan lacks them can't borrow room from the other.

For the account types this builds on, start at the investing hub.