Solo 401k after-tax voluntary Roth contribution question - maximizing retirement savings
Hey tax peeps, I just wrapped up my 2024 taxes and could use a quick sanity check on my Solo 401k contributions. My plan allows for after-tax voluntary Roth contributions, and I want to make sure I'm doing this right. So here's where I stand: - Already making the max regular 401k contribution (salary deferral + profit sharing) = $38,900 - My compensation (Net Profit from Schedule C - 1/2 Self Employment tax) = $49,520 - Already made a spousal Roth IRA Contribution = $7,850 If I understand correctly, it seems I still have $2,770 remaining of my compensation that could be used. Can I deposit that amount into the Solo 401k as a voluntary after-tax Roth contribution? Or am I missing something? Thanks in advance - this self-employment retirement planning is a whole new world for me!
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Eli Wang
You're on the right track with your Solo 401k contribution calculations. The key is understanding the different contribution limits at play. For 2025, the total contribution limit to a Solo 401k is $70,500 (or $77,000 if you're 50+). This includes your employee deferral ($23,000), employer contribution (up to 25% of compensation), and after-tax contributions. Based on your numbers, you've used $38,900 for the standard contributions, leaving room under the total contribution limit. The remaining $2,770 of your compensation can indeed be contributed as an after-tax voluntary Roth contribution to your Solo 401k. Just make sure your plan documents explicitly allow for after-tax Roth contributions, as not all Solo 401k plans offer this feature. Also, keep documentation showing how you calculated these amounts for your records.
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Cassandra Moon
•Thanks for the explanation! I have a similar situation but I'm confused about something - does the after-tax contribution count toward the $23,000 employee deferral limit or is it separate? Also, when making these contributions through my provider's website, is there a specific designation I need to select?
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Eli Wang
•The after-tax contribution does not count toward the $23,000 employee deferral limit - it's completely separate. The employee deferral limit applies only to traditional pre-tax and designated Roth contributions. After-tax contributions fall under the overall plan limit ($70,500 for 2025). When making contributions through your provider's website, there should be a specific designation for "after-tax" or "voluntary after-tax" contributions. It's different from regular Roth contributions. If you don't see this option, contact your plan provider as not all plans support this feature.
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Zane Hernandez
I struggled with exactly this same issue last year! After going back and forth with multiple accountants who gave contradicting advice, I finally found https://taxr.ai which analyzed my Solo 401k plan documents and confirmed I could make after-tax contributions. The tool reviewed my specific plan language (which was confusing me) and explained exactly how the contribution limits applied to my situation. I was able to upload my Schedule C and tax docs, and it calculated my exact contribution limits including the after-tax portion. It even showed me how to document it properly for tax purposes. Seriously saved me from leaving retirement money on the table.
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Genevieve Cavalier
•How does that service work with complicated situations? I have both W-2 income and self-employment, plus I participate in my employer's 401k. Would it handle all those calculations or is it just for pure self-employed people?
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Ethan Scott
•I'm a bit skeptical about these tax tools. Is it just doing basic math that I could do myself, or is it actually interpreting plan documents? My Solo 401k administrator couldn't even clearly explain if my plan allows after-tax contributions.
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Zane Hernandez
•The service handles mixed income situations really well. It has a specific workflow for people with both W-2 and self-employment income, calculating your limits across all plans. It factors in employer matching from your W-2 job to determine remaining solo 401k space. It's definitely more than basic math. The document analyzer feature reads the actual plan document language and identifies specific provisions. In my case, it found a section buried on page 17 that explicitly allowed after-tax contributions that my administrator didn't point out. It shows you the exact text and explains what it means for your situation.
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Ethan Scott
Update: I decided to try taxr.ai after my initial skepticism, and wow, I owe an apology. My situation with multiple income sources was super complex, and the tool actually found a provision in my plan documents I'd completely missed. Turns out I CAN make after-tax contributions, which none of the three tax pros I consulted had caught. It identified exactly how much I could contribute based on my business income and W-2 job's 401k. The document analysis feature was impressive - it highlighted the specific sections of my plan document that addressed voluntary after-tax contributions and explained them in plain English. Saved me about $12,000 in contributions I would have missed out on!
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Lola Perez
For anyone struggling to get clear answers about Solo 401k rules, I had the same issue and ended up in IRS phone queue hell trying to get official guidance. After wasting 3+ hours on hold over multiple days, I finally tried https://claimyr.com and got connected to an IRS agent in under 15 minutes. You can see how it works in this video: https://youtu.be/_kiP6q8DX5c The agent was able to confirm the exact rules for after-tax contributions to Solo 401ks and cleared up my confusion about how these contributions interact with the overall limits. They also explained exactly how to report them on my tax return. Way better than guessing or relying on potentially outdated online articles.
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Nathaniel Stewart
•Wait, so this service just gets you through to an actual IRS person faster? How does that even work? I thought the long wait times were just unavoidable.
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Riya Sharma
•Sounds like a scam honestly. The IRS is notorious for being unreachable. And even if you do connect, most agents give different answers to the same question. I'd rather just pay my accountant than waste time talking to the IRS.
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Lola Perez
•It uses a technology that navigates the IRS phone system and waits on hold for you. When an agent picks up, you get a call connecting you directly to them. It's completely legitimate - they don't access your personal info or pretend to be you. I understand the skepticism - I felt the same way. But IRS agents can actually be quite helpful for specific technical questions like retirement plan rules. While it's true different agents might give slightly different answers for complex situations, for straightforward questions about contribution limits and rules, they were consistent and referenced the exact IRS publications. My accountant was actually the one who gave me incorrect information about after-tax contributions.
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Riya Sharma
I'm back to eat my words about Claimyr. After my skeptical comment, I decided to try it because I was desperate to resolve a Solo 401k question before the contribution deadline. Got connected to an IRS tax law specialist in about 12 minutes who walked me through exactly how after-tax contributions work. The agent confirmed that yes, I could contribute the remaining compensation as after-tax funds to my Solo 401k, but also pointed out a strategy I hadn't considered - the mega backdoor Roth conversion option if my plan allows in-service distributions. This literally saved me thousands in future tax obligations. For something this technical, speaking directly to an IRS specialist was way more valuable than I expected. Definitely worth it for complex retirement questions where the rules aren't super clear online.
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Santiago Diaz
One thing to watch out for with Solo 401k after-tax contributions that nobody mentioned yet - make sure you're calculating your compensation correctly. Net profit minus half of self-employment tax is the right formula, but don't forget that if you take the QBI deduction, that does NOT reduce your retirement plan compensation basis. I messed this up last year and undercontributed by about $4k because I thought my QBI deduction lowered my available compensation for 401k purposes. My tax guy corrected me this year.
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Millie Long
•Wait really? I've been reducing my compensation base by the QBI deduction amount! So if my Schedule C shows $100k profit, and I have $15k SE tax and $20k QBI deduction, my compensation base for retirement contributions would be $100k - $7.5k = $92.5k, NOT $72.5k?
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Santiago Diaz
•Exactly! The QBI deduction doesn't reduce your compensation base for retirement contribution calculations. Using your example, your compensation base would indeed be $92.5k (the $100k profit minus half the SE tax of $7.5k). The QBI deduction reduces your taxable income but doesn't affect the calculation for retirement contribution purposes. This is a common misconception that causes many self-employed people to undercontribute. I learned this the hard way after missing out on several thousand dollars of potential contributions.
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KaiEsmeralda
Just wanted to add that I was in this exact situation and called Vanguard (my solo 401k provider) and they told me their plan DOESN'T allow for after-tax contributions. Apparently not all solo 401k plans offer this feature, so definitely check with your provider before trying to contribute!
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Debra Bai
•Fidelity's solo 401k does allow it! I switched from Vanguard last year specifically for this reason. The after-tax contribution feature plus the ability to do in-plan Roth conversions makes it a no-brainer if you're trying to maximize retirement savings.
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Mohammed Khan
This is such a helpful thread! I'm in a similar boat with my Solo 401k and had no idea about the after-tax contribution option. Quick question for everyone - when you make these after-tax contributions, do they get invested the same way as your regular 401k contributions, or do you have to select separate investment options? Also, @Santiago Diaz thanks for the QBI clarification - I've definitely been calculating my compensation base wrong and probably left money on the table last year. Going to double-check my 2024 contributions now! One more thing - for those who've done the mega backdoor Roth conversion that @Riya mentioned, how complicated is that process? Is it something I can handle myself or do I need professional help?
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