Mega Backdoor Roth
The 2026 401(k) limit is not $24,500. Total contributions from all sources can reach $72,000. If your plan allows after-tax contributions and in-plan Roth conversion, you can fill the gap with after-tax money and convert it to Roth, often $30,000 or more a year growing tax-free for life.
Reviewed by Ebot Mbi, CPA, EA · Last reviewed October 9, 2026
Who it fits
- Employees whose 401(k) allows after-tax (non-Roth) contributions and in-service conversion or withdrawal.
- High earners who already max the $24,500 deferral and still have cash to save.
- Business owners who can design their own plan to permit it, often in a solo 401(k).
- Savers who want large Roth balances and are past the backdoor Roth IRA's $7,500.
Who it's not for
- Employees whose plan does not offer after-tax contributions. This is a plan feature, not a personal choice.
- Highly compensated employees in plans that fail nondiscrimination testing; contributions can be refunded.
- Anyone who needs this cash for current needs or debt.
How it works
Three layers fill a 401(k): your deferral of $24,500, the employer's match or profit sharing, and after-tax contributions. Together they cannot exceed $72,000 in 2026. Age-50 catch-up contributions sit on top and do not count toward that cap.
After-tax contributions are not deductible and not Roth. Their growth is taxable when it comes out. The move is to convert them to Roth quickly, inside the plan or by rolling them to a Roth IRA, so there is little or no growth to tax.
Once converted, the money follows Roth rules: no tax on qualified withdrawals.
For an owner with a solo 401(k), the plan document must be written to allow after-tax contributions and in-plan conversions. Many standard documents do not.
Illustrative example
Illustrative: a 45-year-old executive defers $24,500 and receives a $12,000 employer match. The plan permits after-tax contributions with automatic in-plan Roth conversion.
- Room under the $72,000 cap: $72,000 - $24,500 - $12,000 = $35,500.
- After-tax contribution: $35,500, converted to Roth each pay period.
- Taxable amount on conversion: only the small earnings before each conversion.
- Ten years at $35,500 a year: $355,000 contributed to Roth.
- At an illustrative 6% annual return, the balance after 10 years is about $467,918, of which $112,918 is growth that is never taxed.
About $355,000 moved into Roth over ten years, with roughly $113,000 of growth that never faces income tax at an illustrative 6% return.
The rules
| Rule | Citation |
|---|---|
| Total annual additions to a defined contribution plan are capped, $72,000 for 2026, excluding catch-up contributions. | IRC §415(c) |
| Plans may permit in-plan rollovers of non-Roth amounts to a designated Roth account. | IRC §402A(c)(4) |
| After-tax and pre-tax amounts in a distribution can be directed separately to Roth and traditional destinations. | IRS Notice 2014-54 |
| After-tax employee contributions are subject to nondiscrimination testing. | IRC §401(m) |
Watch-outs
- Delay between contribution and conversion creates taxable earnings. Ask whether the plan offers automatic conversion.
- In plans with many highly compensated employees, the ACP test can force refunds of after-tax contributions.
- If you change jobs mid-year, the $72,000 cap generally applies per employer, but deferrals are limited per person. Track both.
- Converted amounts reported on Form 1099-R must match the after-tax basis, or the IRS can treat the conversion as taxable.
What we do
We read your plan's summary, confirm the after-tax and conversion features, and size the contribution against the $72,000 cap. For owners, we work with your plan provider to write the feature into the plan document. We reconcile the 1099-R and basis each year.
Questions
How do I know if my plan allows this?
Look in the summary plan description for after-tax contributions and in-plan Roth conversions or in-service distributions. We can read it for you.
Can I do both the backdoor Roth IRA and the mega backdoor?
Yes. They are separate limits. One uses an IRA, the other your employer plan.
Is the conversion taxable?
Only the earnings on the after-tax money before conversion. The after-tax contribution itself was already taxed.