If you have already maxed out your 401(k), you may still have room to save more at work. The amount will depend on federal limits and whether your employer adds money to your account. A mega backdoor Roth could turn that extra room into tax-free retirement savings. Here’s an example of how this strategy could help you add another $40,000 to your nest egg.
Why the Standard Limits Aren’t the Real Ceiling
For 2026, employees younger than 50 can contribute up to $24,500 into a traditional or Roth 401(k). Workers 50 and older can add an $8,000 catch-up contribution, and those ages 60 to 63 can add $11,250 instead. 1
A separate defined contribution plan limit of $72,000 generally caps how much you can save in the plan. 2 This amount excludes catch-up contributions, but includes elective deferrals, employer matching and after-tax contributions. Here is a roundup of the 2026 limits:
| Contribution Type | 2026 Limit |
|---|---|
| Employee elective deferrals (pretax or Roth) | $24,500 |
| Catch-up contributions, age 50 and older | $8,000 |
| Catch-up contributions, ages 60 to 63 | $11,250 |
| Total defined contribution plan limit | $72,000 |
The mega backdoor Roth lets you make additional after-tax 401(k) contributions after you’ve reached the $24,500 elective deferral limit. The amount available depends on the $72,000 annual limit and any employer contributions. You can convert those after-tax dollars to a Roth.
Unlike a Roth IRA, capped at $7,500 for 2026 with income phase-outs, it has no income limit. It generally works best after you’ve captured your employer match, reached the regular 401(k) cap and, if eligible, funded that IRA.
Your plan must allow after-tax contributions and either in-plan conversions or rollovers. For tax purposes, these contributions aren’t deductible, but once converted, earnings grow tax-free and qualified withdrawals aren’t taxed.
A financial advisor can help you evaluate how a mega backdoor Roth could affect your long-term retirement savings.
Running the Numbers
To show how you may be able to add $40,000 to your nest egg with a mega backdoor Roth strategy, let’s break down an example of a 40-year-old employee who contributed the full $24,500 in 2026. Their employer matches $7,500.
The table breaks down how much they could add to their retirement savings, along with how the amount changes with different employer contributions on a $150,000 salary:
| Employer Contribution | Amount | Calculation | After-Tax Room |
|---|---|---|---|
| None | $0 | $72,000 − $24,500 − $0 | $47,500 |
| 2% match | $3,000 | $72,000 − $24,500 − $3,000 | $44,500 |
| 5% match (example) | $7,500 | $72,000 − $24,500 − $7,500 | $40,000 |
| 5% match plus 5% profit sharing | $15,000 | $72,000 − $24,500 − $15,000 | $32,500 |
A more generous employer contribution leaves less room for after-tax contributions, while the combined contributions can reach the $72,000 annual-additions limit. If the plan permits it, the full $40,000 can go in as after-tax contributions and then be converted to a Roth.
How Contributing $40,000 More Could Affect Your Nest Egg
With a mega backdoor Roth, after-tax contributions are made with money that has already been taxed. The contribution itself generally isn’t taxed again when converted to a Roth. To contribute $40,000, you first need to earn enough to cover both the contribution and the taxes on it.
A single filer earning $150,000 who defers the full $24,500 pretax would have about $109,400 in taxable income ($150,000 − $24,500 − $16,100 standard deduction). That amount reaches the 24% federal bracket.
Funding the $40,000 would require earning about $52,632 ($40,000 ÷ 0.76). At a 24% marginal federal income-tax rate, roughly $12,632 would go to federal income tax ($52,632 − $40,000).
The table shows how each contribution amount from the previous section could grow at a hypothetical 7% annual return, with no further deposits:
| After-Tax Contribution | After 10 Years | After 20 Years | After 30 Years |
|---|---|---|---|
| $47,500 | $93,440 ($47,500 × 1.07¹⁰) | $183,810 ($47,500 × 1.07²⁰) | $361,582 ($47,500 × 1.07³⁰) |
| $44,500 | $87,538 ($44,500 × 1.07¹⁰) | $172,201 ($44,500 × 1.07²⁰) | $338,745 ($44,500 × 1.07³⁰) |
| $40,000 | $78,686 ($40,000 × 1.07¹⁰) | $154,787 ($40,000 × 1.07²⁰) | $304,490 ($40,000 × 1.07³⁰) |
| $32,500 | $63,932 ($32,500 × 1.07¹⁰) | $125,765 ($32,500 × 1.07²⁰) | $247,398 ($32,500 × 1.07³⁰) |
At a 7% annual return, the table shows the balance nearly doubling every 10 years, growing from a single $40,000 contribution to about $78,700 after 10 years, $154,800 after 20 years and $304,500 after 30 years.
A financial advisor can help you weigh the upfront taxes against years of tax-free growth.
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