What is a mega backdoor Roth?
A mega backdoor Roth is a strategy that lets you funnel substantially more money into Roth accounts than the standard 401(k) limit allows — by routing after-tax (non-Roth) dollars through your employer plan and converting them to Roth. It works inside an employer 401(k) plan: you make after-tax (non-Roth) contributions above the regular elective deferral limit, then convert those after-tax dollars to Roth — either through an in-plan Roth conversion or by rolling them out to a Roth IRA via an in-service withdrawal.
In 2026 the standard elective deferral limit is $24,500, while the total IRS Section 415 limit on all 401(k) contributions (yours + employer) is $72,000. The gap between those two numbers, minus your employer match, is your mega backdoor Roth room.
The reason it matters for high earners: direct Roth IRA contributions are phased out above certain income thresholds, so most high-income employees can't fund a Roth IRA the normal way. The mega backdoor sidesteps those phase-outs entirely because it lives inside the 401(k) plan, where income limits don't apply to contributions.
The result, when your plan supports it, is tens of thousands of extra dollars per year going into a Roth account — money that grows and is withdrawn tax-free in retirement, on top of whatever you're already putting into your regular pre-tax or Roth 401(k). It's primarily for high earners at companies whose plans support both after-tax contributions and in-plan conversions — Google, Amazon, Meta, Apple, Microsoft, and many other large employers.
2026 mega backdoor Roth limits
Three buckets share one combined ceiling. The Section 415(c) total annual additions limit for 2026 is $72,000, and it covers (1) your own elective deferrals (pre-tax or Roth), (2) any employer match or profit sharing, and (3) any after-tax contributions you make. Your maximum after-tax — and therefore mega backdoor — space is what's left over after the first two buckets.
after_tax_room = $72,000 − your_elective_deferral − employer_contributions
If you max your regular deferral at the 2026 limit of $24,500 and receive no employer contribution, your after-tax space is up to $72,000 − $24,500 = $47,500. Employer match reduces it dollar for dollar against the $72,000 cap: with an $8,000 match, your after-tax space drops to $72,000 − $24,500 − $8,000 = $39,500.
Catch-up contributions don't expand the after-tax bucket. Age 50+ adds an extra $8,000 to your deferral (total $32,500), and SECURE 2.0 adds a $11,250 super catch-up for ages 60–63, but those amounts flow into the deferral bucket — the $47,500 ceiling on the after-tax portion stays the same.
Key 2026 numbers
| Limit | Under 50 | Age 50–59 | Age 60–63 |
|---|---|---|---|
| Elective deferrals | $24,500 | $32,500 | $35,750 |
| Total 415 limit | $72,000 | $80,000 | $83,250 |
| Max mega backdoor* | $47,500 | $47,500 | $47,500 |
*Before employer contributions. Actual room = 415 limit − your deferrals − employer contributions. Source: IRS Notice 2025-67, effective January 1, 2026.
Does your 401(k) plan allow it?
This is the single most important question, and the one most articles skip past. The mega backdoor Roth only works if your employer's 401(k) plan offers both (a) after-tax (non-Roth) contributions above the regular deferral limit, and (b) a way to convert those after-tax dollars to Roth — either an in-plan Roth conversion or an in-service withdrawal that lets you roll the money into a Roth IRA while you're still employed.
Plenty of plans allow one without the other, which loses most of the benefit. Large tech employers — Google, Meta, Microsoft, and similar — commonly offer both, which is why the strategy is most associated with that workforce. Before you plan around the mega backdoor, read your summary plan description or call your plan administrator and ask specifically: "Does the plan allow after-tax contributions above the elective deferral limit, and does it allow in-plan Roth conversions or in-service withdrawals of those after-tax dollars?"
Who the mega backdoor Roth is for
The strategy fits best when several conditions line up. You're a high earner who's already maxing the regular 401(k) deferral, you still have meaningful cash flow left over after living expenses and other savings goals, your take-home pay is high enough to actually fund tens of thousands of additional after-tax contributions, and you're phased out of direct Roth IRA contributions. Many people in this profile also receive RSUs or other equity, which adds room to the budget for extra contributions.
If you're not yet maxing your regular pre-tax or Roth deferral, do that first — the dollars going into Roth via the mega backdoor are after-tax, so a regular pre-tax 401(k) contribution gives you an immediate tax deduction the mega backdoor doesn't. The mega backdoor is a layer on top, not a replacement.
Frequently asked questions
How much can I put in a mega backdoor Roth in 2026?
Up to $47,500 if you maxed your $24,500 elective deferral and your employer makes no contributions. Any employer match or profit sharing reduces your after-tax room dollar for dollar against the $72,000 Section 415(c) cap.
Is the mega backdoor Roth the same as a backdoor Roth IRA?
No. A backdoor Roth IRA is a separate strategy that involves contributing to a traditional IRA and then converting it to a Roth IRA — used by high earners phased out of direct Roth IRA contributions. The mega backdoor Roth lives inside your 401(k) and moves far larger dollar amounts.
Do I pay taxes on the conversion?
The after-tax principal you contributed is generally not taxed again at conversion — you already paid income tax on those dollars. Any earnings that accumulated before the conversion are taxable as ordinary income. Converting promptly (often automatically, if your plan supports daily or weekly conversions) minimizes those taxable earnings.
What if my employer matches — does that reduce my space?
Yes. Employer match and profit-sharing dollars count against the $72,000 total annual additions cap, so they directly reduce the after-tax room left for the mega backdoor. The bigger your match, the smaller your mega backdoor ceiling.
What happens if my plan doesn't allow in-plan conversions?
If after-tax contributions are allowed but in-plan conversions and in-service withdrawals aren't, the strategy mostly doesn't work. After-tax dollars left in the 401(k) grow tax-deferred but not tax-free — earnings on them are taxed as ordinary income at distribution, which loses the main benefit. Without a conversion mechanism, most people skip the strategy.
Is the mega backdoor Roth going away?
It's currently allowed under federal tax law in 2026. Proposals to limit or eliminate it have surfaced periodically, but no such change is in effect today. We won't speculate on future law — for the current tax year, if your plan supports it, the strategy is available.
This calculator and its explanations are educational and give estimates only — not investment, tax or legal advice. Real returns, inflation and tax outcomes vary; talk to a qualified professional about your own situation.