Many self-employed professionals believe they’ve permanently missed the opportunity to use the Mega Backdoor Roth once December 31 passes. The good news?
That assumption is often wrong.
Watch: Learn how you can still make solo 401k voluntary after-tax contributions for 2025 in 2026 and process the Mega Backdoor Roth Solo 401k strategy
With the right Solo 401(k) plan design, you can still open a Solo 401(k) in 2026 and make Mega Backdoor Roth contributions for tax year 2025 — and you can do it while using Fidelity as the brokerage.
Here’s how it works, who qualifies, and why this strategy remains one of the most powerful Roth-building tools available to self-employed individuals.
What Is the Mega Backdoor Roth Solo 401(k)?
The Mega Backdoor Roth Solo 401(k) strategy allows you to:
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Make voluntary after-tax contributions to a Solo 401(k)
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Then convert those funds to:
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A Roth Solo 401(k), or
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A Roth IRA
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Allow the converted funds to grow tax-free for life
For tax year 2025, the overall Solo 401(k) contribution limit is $70,000.
That entire amount can potentially be routed into Roth status using this strategy.
Yes — You Can Open the Plan in 2026 for 2025 Contributions
Thanks to SECURE Act 2.0 rule changes, voluntary after-tax Solo 401(k) contributions follow the business tax-return deadline (including extensions) — not December 31.
That means plan adoption and funding can occur in 2026 and still count for tax year 2025.
Deadlines by Business Type
Sole Proprietors & Single-Member LLCs (Disregarded Entities)
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April 15, 2026 — open & fund for 2025
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October 15, 2026 — if a timely extension is filed
S-Corporations & Partnerships
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March 15, 2026 — open & fund for 2025
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September 15, 2026 — with a timely business-return extension
Why Fidelity Works with My Solo 401k Financial
Fidelity does not offer a Solo 401(k) that supports Mega Backdoor Roth contributions.
However, Fidelity does support non-prototype retirement brokerage accounts, which can be used to hold a custom Solo 401(k) provided by My Solo 401k Financial.
With a solo 401k plan from My Solo 401k Financial:
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You choose Fidelity, Schwab, or another brokerage
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Your funds are never held by us
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Fidelity recognizes My Solo 401k Financial as the plan provider
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We handle the required IRS reporting
This gives you institutional-level flexibility with full Mega Backdoor Roth support.
How the Account Structure Works
A properly designed Solo 401(k) separates money by source, not by plan:
One Participant Plan
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Pre-Tax Solo 401(k) account
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Roth Solo 401(k) account
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Voluntary After-Tax Solo 401(k) account
Spousal (Two-Participant) Plan
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Each spouse has their own set of three accounts
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Still one Solo 401(k) plan, sponsored by the business
After-tax contributions flow into the after-tax account and are then converted to Roth.
Converting Voluntary After-Tax Solo 401k Contributions to the Roth Solo 401(k) vs Roth IRA — Why Many Choose Roth Solo 401(k)
Many clients prefer converting to their solo 401k voluntary after-tax solo 401k contributions to the Roth Solo 401(k) instead of a Roth IRA because:
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No required minimum distributions (SECURE Act 2.0)
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Ability to invest in real estate, crypto, notes, metals
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Eligible for participant loans
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Easier consolidation under one plan
That said, the choice is always yours.
IRS Reporting — We Handle the Heavy Lifting
My Solo401k Financial supports:
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Form 1099-R for conversions & distributions (upon request)
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Form 5500-EZ once plan assets exceed $250,000 (upon request)
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Online request forms for all reporting
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Ongoing compliance support
You maintain control of the funds — we handle the compliance.
Bonus: $1,500 Solo 401(k) Auto Contribution Tax Credit
Our Solo 401(k) plans include the SECURE Act auto-contribution feature, which qualifies for:
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$1,500 in tax credits
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Claimed as $500 per year over three years
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Filed on IRS Form 8881
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A dollar-for-dollar reduction in tax owed
Most brokerage-only Solo 401(k) plans do not include this credit.
Bottom Line
If you’re self-employed and missed the December 31 setup deadline, you may still be able to unlock up to $70,000 in Roth savings for 2025.
By opening a custom Solo 401(k) in 2026 with MySolo401k Financial and using Fidelity as your brokerage, you can still execute a Mega Backdoor Roth — legally, compliantly, and efficiently.
