What is a Mega Backdoor Roth?

A Mega Backdoor Roth is a strategy that moves after-tax contributions from a 401(k) into a Roth account, letting you put far more into Roth savings than the standard Roth IRA or Roth 401(k) limits allow on their own. You make extra after-tax contributions to your workplace plan, then convert that money to Roth so it can grow tax-free.

The “mega” distinguishes it from the ordinary backdoor Roth IRA, which moves at most a few thousand dollars a year through a nondeductible IRA. The mega version runs through your 401(k) instead, where the total contribution ceiling is much higher, so a saver who has already maxed out every other tax-advantaged account can direct tens of thousands of additional dollars into Roth annually.

How the Mega Backdoor Roth Works

The strategy relies on the gap between what you can contribute to a 401(k) as an employee and the higher overall limit the Internal Revenue Code (IRC) sets on total contributions to the plan. It comes together in three steps.

1. Contribute your elective deferral. Put in up to the standard employee limit through pre-tax or Roth 401(k) contributions. For 2026 that limit is $24,500, or $32,500 if you are 50 or older, or $35,750 if you are 60 to 63, since the $11,250 catch-up for that age group replaces the $8,000 one.
2. Add after-tax contributions. If your plan allows it, contribute additional after-tax dollars toward the overall Section 415© limit on everything that can go into the plan. For 2026 that limit is $72,000 or 100% of your compensation, whichever is lower, and it counts your elective deferral, any employer contributions, and your after-tax contributions together. Catch-up contributions sit on top of it.
3. Convert the after-tax money to Roth. Move those after-tax contributions into Roth through an in-plan Roth conversion or a rollover to a Roth IRA. This is the step that turns ordinary after-tax savings into a Roth balance that grows and comes out tax-free.

Does My 401(k) Allow a Mega Backdoor Roth?

The strategy only works if your employer’s plan supports two specific features:

• After-tax contributions. These are a separate contribution type, distinct from pre-tax and Roth 401(k) deferrals. Without an after-tax bucket, there is no extra money to convert.
• In-service conversions or withdrawals. You need a way to move the after-tax money into Roth while you are still employed, either through an in-plan Roth conversion or an in-service withdrawal you roll to a Roth IRA. If the plan makes you wait until you leave, the after-tax money sits there accumulating taxable earnings until you do.

Confirm both with your plan administrator or in the summary plan description before you start. Solo 401(k) plans for the self-employed can also support the strategy, but only if the plan document specifically allows after-tax contributions and in-plan conversions, and not every provider’s document does.

Nondiscrimination Testing for Highly Compensated Employees

Even when a plan offers after-tax contributions, highly compensated employees (HCEs) may not be able to use the full $72,000. After-tax contributions and employer matching contributions are both subject to the actual contribution percentage (ACP) test, which compares the average contribution rate of HCEs with that of everyone else in the plan. If HCEs contribute too much relative to rank-and-file employees, the plan fails the test and has to refund the excess to HCEs.

To avoid refunds, some plans cap after-tax contributions for HCEs at a set percentage of pay, and the cap can change from year to year based on how the rest of the workforce saves. If you are an HCE, ask your plan administrator what after-tax limit applies to you; that number, not $72,000, is your practical ceiling.

How Mega Backdoor Roth Conversions Are Taxed

After-tax contributions themselves convert to Roth tax-free, since you already paid tax on that money. Any earnings those contributions generate before you convert are pre-tax, though, so converting them adds to your taxable income for the year.

Convert soon after each contribution and there is little or no growth to be taxed. Let the after-tax money sit and compound for months, and the gains you eventually convert become a taxable event. Some plans handle this automatically by sweeping after-tax contributions into Roth on a set schedule; others leave the timing to you. When earnings do accumulate, a distribution or conversion generally carries a proportional (pro-rata) share of those earnings along with your contributions, so you can’t cherry-pick only the contributions.

A rollover out of the plan gives you a way to keep those earnings tax-deferred. Under IRS Notice 2014-54, when a single distribution includes both after-tax contributions and pre-tax earnings, you can direct the pre-tax earnings to a traditional IRA and the after-tax contributions to a Roth IRA. The earnings stay tax-deferred instead of being taxed on conversion, and the after-tax basis lands in Roth.

Mega Backdoor Roth Limit for 2026

The after-tax room is the overall limit minus your elective deferral and any employer contributions. Catch-up contributions raise your total but not your after-tax room, because they sit outside the $72,000.

The after-tax column assumes your compensation at least equals the row’s total employee contributions ($72,000 under 50, $80,000 at 50-59 or 64 and older, $83,250 at 60-63), because your own contributions can’t exceed your pay, and it assumes your plan doesn’t impose a lower HCE cap.

Say you are under 50 and your employer offers no matching contribution. You contribute the full $24,500 elective deferral, which leaves $72,000 - $24,500 = $47,500 of room for after-tax contributions. You contribute that $47,500 in after-tax dollars and convert it through an in-plan conversion or a rollover to a Roth IRA. You have moved $47,500 into Roth in a single year, well beyond the $7,500 that direct Roth IRA contributions would have allowed.

An employer match changes the arithmetic. Because the match counts toward the same $72,000 ceiling, a $10,000 employer contribution would shrink your after-tax room to $37,500.

Set up as a Mega Backdoor Roth flow in ProjectionLab, your after-tax contributions fill whatever room your deferrals and match leave under the overall limit, then convert either in-plan or to a Roth IRA.

Frequently Asked Questions

How much can you put in a mega backdoor Roth in 2026? Up to $47,500 if you contribute the full $24,500 elective deferral and receive no employer contributions. That figure is the $72,000 overall 2026 limit minus your $24,500 deferral. Employer contributions reduce the after-tax room dollar for dollar, your plan may set a lower cap if you are a highly compensated employee, and the total can’t exceed 100% of your compensation. Catch-up contributions sit outside the $72,000, so they raise the total without adding after-tax room.

What is the difference between a mega backdoor Roth and a backdoor Roth? Scale and mechanics. A backdoor Roth IRA moves up to the annual IRA limit ($7,500 in 2026) through a nondeductible traditional IRA, and it exists to get around the Roth IRA income phase-outs (which run from $153,000 to $168,000 for single filers and $242,000 to $252,000 for married couples filing jointly in 2026). A Mega Backdoor Roth runs through your 401(k) instead, using after-tax contributions and in-plan conversions to move as much as $47,500. You can do both in the same year.

What are the tax implications of a mega backdoor Roth? The after-tax contributions convert to Roth tax-free because you already paid income tax on them. Only the investment earnings that accrue between contributing and converting are taxable, which is why converting quickly keeps the tax bill near zero. If you roll the money out of the plan instead, you can send those earnings to a traditional IRA and avoid the tax for now. Once inside the Roth account, the money grows and, in qualified distributions, comes out entirely tax-free.