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Mega Backdoor Roth Solo 401k — How Does It Work and Is It Taxable?
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1 Reply
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I’ve been hearing a lot about the Mega Backdoor Roth Solo 401k. My income is too high for direct Roth IRA contributions, and I’ve already maxed out my regular Roth employee deferrals. Someone told me voluntary after-tax contributions can let me put even more into Roth. How does this work, and is the conversion taxable?
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The Mega Backdoor Roth Solo 401k strategy allows self-employed individuals to contribute significantly more to their Roth Solo 401k than the standard employee deferral limit — using voluntary after-tax contributions that are immediately converted to the Roth Solo 401k. My Solo 401k Financial’s plan documents explicitly support this strategy.
Here is how it works, step by step:
- Max out employee elective deferrals ($24,500 for those under age 50 in 2026) as Roth or pre-tax
- Make the maximum employer profit-sharing contribution (25% of W-2 wages for S-Corps; 20% of net SE income for sole proprietors)
- Calculate the remaining headroom under the $72,000 §415(c) overall limit
- Contribute that remaining amount to the voluntary after-tax Solo 401k holding account
- Immediately convert those funds to the Roth Solo 401k — this is the Mega Backdoor Roth conversion
On the tax question: Voluntary after-tax contributions themselves are not deductible — they are made with after-tax dollars. However, when the conversion to the Roth Solo 401k is done promptly (while earnings are minimal), it is largely a non-taxable but reportable event. Once inside the Roth Solo 401k, those funds grow completely tax-free, and qualified distributions at retirement are tax-free and penalty-free. My Solo 401k Financial issues all required reporting forms for plan clients who execute this strategy.
Example: A sole proprietor (age 45) with $150,000 in net self-employment income in 2026 makes a $24,500 Roth employee deferral and a $27,880 employer profit-sharing contribution. The remaining headroom under the $72,000 §415(c) limit is approximately $19,620. Contributing that $19,620 as a voluntary after-tax contribution and immediately converting to the Roth Solo 401k adds over $20,000 in additional Roth savings — on top of the standard Roth deferral already made.
mysolo401k.net
The Mega Back Door Roth Using a Solo 401k Plan - My Solo 401k Financial
Learn how our Roth Solo 401k plan can allow you to maximize Roth contributions using the Mega Back Door Roth.
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