A mega backdoor Roth moves extra retirement savings into Roth through a workplace plan. You make after-tax contributions to a 401(k), separate from regular pre-tax or Roth contributions, then convert or roll that money into Roth. Your plan must allow both steps. For 2026, the combined contribution limit is generally $72,000 before catch-ups, but employer contributions and regular employee deferrals use part of it.
What is a mega backdoor Roth?
The name describes a strategy, not a separate account. It relies on a third contribution option some 401(k) plans offer:
| Contribution type | Tax treatment going in | Which 2026 limit applies? |
|---|---|---|
| Pre-tax 401(k) deferral | Generally reduces current taxable income | Shares the $24,500 regular employee limit with Roth deferrals |
| Roth 401(k) deferral | No current income-tax deduction | Shares the same $24,500 regular employee limit |
| After-tax, non-Roth contribution | No current income-tax deduction | Uses room left under the combined $72,000 limit |
An after-tax contribution is not yet Roth money. Its earnings remain pre-tax until converted or otherwise distributed. The conversion or rollover is what completes the strategy.
The backdoor Roth IRA uses a separate IRA contribution and conversion. The similar names hide different account rules.
How does a mega backdoor Roth work?
- Confirm the plan permits it. You need after-tax employee contributions and a Roth conversion or eligible rollover route.
- Calculate your remaining room. Include expected employer matching and profit-sharing contributions, not just deposits made so far.
- Make the after-tax contribution. Select the after-tax, non-Roth contribution source in the plan.
- Move it to Roth. Use an in-plan Roth conversion or an eligible rollover to a Roth IRA, following the administrator’s process.
- Check the tax reporting. Keep records of contributions, earnings, and Forms 1099-R.
Some plans permit frequent or automatic conversions. Others limit when money can move. A long delay can let taxable earnings accumulate; a quick conversion may leave little growth to tax. Neither route creates a new deduction for the after-tax contribution.
What is the mega backdoor Roth limit for 2026?
There is no separate IRS limit called the “mega backdoor Roth limit.” For a typical 401(k), total annual additions are limited to the lesser of $72,000 or 100% of compensation in 2026. Annual additions include regular employee deferrals, employer contributions, after-tax contributions, and any allocated forfeitures. Eligible catch-ups sit outside that combined limit.
The IRS publishes the 2026 combined limits and employee deferral limits. Here is the calculation for an employee with at least $72,000 of compensation and no allocated forfeitures:
| Item | Amount |
|---|---|
| Combined 2026 limit | $72,000 |
| Regular employee deferrals | −$24,500 |
| Employer match and profit sharing | −$12,000 |
| Potential after-tax contribution room | $35,500 |
That $35,500 is available only if the plan permits it. If the employer later adds another $3,000, the room falls to $32,500. Leave space for contributions expected later in the year and any plan-specific cap.
Our 401(k) contribution guide explains the separate employee, combined, and catch-up limits.
Does my 401(k) allow a mega backdoor Roth?
Look for these two features in the summary plan description, then confirm them with the administrator:
- After-tax employee contributions, distinct from Roth salary deferrals.
- An in-plan Roth conversion or an eligible in-service rollover, allowing money to move while you still work there.
Ask how often conversions are allowed, whether they can happen automatically, and whether the plan limits contributions for highly compensated employees. Nondiscrimination testing can reduce what you may contribute even when the federal calculation shows room.
A plan that offers only pre-tax and Roth salary deferrals does not provide the after-tax contribution step. A plan that accepts after-tax money but will not let it move to Roth until you leave requires a different decision: earnings can accumulate in the meantime, and that money remains subject to the plan’s withdrawal rules.
Are earnings on after-tax 401(k) contributions taxable?
Earnings are generally taxable if you move them into Roth; the contribution itself is not taxed again. Suppose you contribute $10,000 after tax and it grows to $10,200 before conversion. Moving the full $10,200 to Roth generally adds $200 to taxable income.
For an eligible rollover, the IRS allows after-tax contributions to go to a Roth IRA and pre-tax earnings to a traditional IRA. Work with the administrator on the allocation; you cannot assume any withdrawal consists only of after-tax dollars.
Sending earnings to a traditional IRA avoids converting those dollars now, but can complicate a separate backdoor Roth IRA strategy. Pre-tax IRA balances enter that strategy’s pro-rata calculation. Compare the small current conversion tax with the consequences of creating a pre-tax IRA balance.
Also distinguish the conversion from a later withdrawal. Moving money into Roth does not automatically make every future withdrawal tax-free. The account’s qualification and distribution rules still apply.
Can you do a backdoor Roth and a mega backdoor Roth in the same year?
Yes, if you meet the rules for each. An IRA contribution does not use up the 401(k)’s combined limit. For 2026, the IRA contribution limit is $7,500, or $8,600 for someone age 50 or older, subject to the usual eligibility rules.
Keep the two checks separate: the IRA strategy requires checking pre-tax IRA balances and Form 8606; the workplace strategy requires checking plan features and combined contribution room. Before choosing either, preserve cash for near-term bills. Extra Roth savings are useful only if you can afford to leave the money invested.