Mega Backdoor Roth: How High Earners Save Up to $47,500 More Per Year
Last verified: 2026-02-04, against IRS Notice 2025-67 (2026 retirement plan limits).
If your employer's 401(k) plan allows it, the mega backdoor Roth is the largest single Roth contribution most people will ever make. It lets high earners stash up to $47,500 a year (2026) of after-tax dollars into a Roth account that grows tax-free forever.
How it works in three steps
- Max your regular 401(k): Put in the $24,500 employee deferral first (pre-tax or Roth, your choice).
- Make after-tax (not Roth) contributions: Most plans that support this strategy let you contribute additional dollars on an after-tax basis, up to the $72,000 415(c) total.
- Convert immediately: Roll the after-tax balance into the Roth side of the same 401(k) (an "in-plan Roth conversion") or to a Roth IRA. Doing it quickly avoids taxes on growth.
The math
2026 415(c) cap is $72,000. Subtract:
- $24,500 regular employee deferral
- Your employer match (let's say $0–$10,000)
What is left is your after-tax / mega backdoor headroom. With no match, that is $47,500 a year of additional Roth contributions. That is more than six times the regular $7,500 Roth IRA limit.
Three things your plan must allow
- After-tax contributions (separate from Roth deferrals)
- In-plan Roth conversions, or in-service withdrawals of after-tax dollars to a Roth IRA
- No "anti-discrimination" testing limits that cap you below the IRS limit
If your plan does not allow after-tax contributions or in-plan conversions, you cannot use this strategy. Many large-company plans (Microsoft, Meta, Google, Amazon among them) do allow it. Smaller employers often do not.
How to ask your plan administrator
Email or call HR and ask exactly: "Does our 401(k) plan permit after-tax employee contributions above the standard 402(g) elective deferral limit? And does it permit in-plan Roth conversions of those after-tax balances?" If both answers are yes, you can run the strategy.
Common mistakes
- Confusing after-tax with Roth. They are different. After-tax contributions sit in a separate sub-account that must be converted to become Roth.
- Waiting too long to convert. Earnings on after-tax dollars are taxable when converted. Convert quickly (ideally automatically) so there is little to no growth in between.
- Forgetting the match counts. Employer match eats into your $72,000 cap, reducing your after-tax headroom.
Curious how big your mega backdoor opportunity is? Explore the free educational tool calculates it automatically based on your income, employer match, and plan features.
Frequently Asked Questions
How much can I contribute with a mega backdoor Roth in 2026?
Begin with the $72,000 415(c) limit for 2026, subtract the $24,500 you contribute as an elective deferral, and then subtract whatever your employer contributes on your behalf. Whatever remains is your after-tax capacity. A participant receiving no employer match therefore has roughly $47,500 of additional Roth capacity, which is more than six times the ordinary Roth IRA limit.
How do I know whether my 401(k) plan allows the mega backdoor Roth?
The question turns on two plan provisions, and you need both of them. Ask your plan administrator whether the plan permits after-tax employee contributions above the standard 402(g) elective deferral limit, and whether it permits in-plan Roth conversions of those after-tax balances. Large employers frequently allow both; smaller plans often allow neither, because each provision adds administrative and nondiscrimination-testing complexity.
Are after-tax 401(k) contributions the same as Roth contributions?
They are distinct contribution types, and the distinction is precisely what makes the strategy possible. A Roth deferral counts against the $24,500 elective deferral limit, while an after-tax contribution sits above that limit and counts only toward the $72,000 annual additions ceiling. Without that separation there would be no room left to fill.
Will I owe tax when I convert the after-tax money to Roth?
Tax applies only to earnings, meaning whatever those after-tax dollars generated between the date of contribution and the date of conversion. Converting promptly keeps that figure close to zero, which is why the mechanics call for conversion immediately rather than at year end. An after-tax balance left invested for several months before conversion produces a taxable amount that could have been avoided entirely.