A self-directed solo 401k from My Solo 401k Financial allows for voluntary after-tax contributions.
After making your solo 401k voluntary after-tax contributions to the Fidelity brokerage account (a.k.a. non-prototype/investment only) that was setup to separately hold the voluntary after-tax solo 401k contributions, the next step is convert them to the Roth solo 401k brokerage account also held at Fidelity Investments.
Using the Fidelity Investments Form to Internally Move the Funds
To move funds from your voluntary after-tax solo 401k Fidelity brokerage account (non-prototype) into your Roth solo 401k Fidelity brokerage account, complete the Fidelity form titled “One-Time Withdrawal Investment Only Retirement Account.”
CLICK HERE to download the form.
How to Complete Fidelity Investments Form
Under Section 1-Plan and Trust Information
Account Number: Enter your solo 401k Voluntary After-Tax Fidelity brokerage account number.
Name of Trustee: Enter your name.
Name of Employer Plan: Enter the name of your solo 401k plan.
Name of Plan Participant: Enter your name.
Daytime Phone: Enter your phone number.
Under Section 2-Distribution Instructions
Select “only the following amount of cash in your account” and enter the dollar amount of voluntary after-tax solo 401k funds that you wish to convert to the Roth solo 401k.
Under Section 2-Distribution Instructions
Choose 3b “Direct rollover/conversion into another retirement account held with Fidelity.”
Select the 2nd box titled “Fidelity Investment-Only Account (formerly known as a Non-Prototype account)…”
Fidelity Account Number: Enter your Roth solo 401k Fidelity brokerage account number.
Account Owner Name: Enter your name since you are the owner of the solo 401k.
Under Section 4-Signature and Date
Print Trustee Name: Enter your name.
Trustee Signature: Sign your legal name.
Date: Enter today’s date.
Submitting the Completed Form to Fidelity Investments
- Take it to a Fidelity Investor Center; or
- Mail the completed Form to Fidelity; or
- Upload it using the Fidelity message center once you login to your Fidelity account.
Our On-Line Conversion Form
After you have Fidelity Investments internally convert the solo 401k voluntary after-tax funds to the Roth solo 401k, the next step is to log the conversion our website using the following link: https://www.mysolo401k.net/after-tax-to-roth-solo-401k-in-plan-conversion-form/
We, (not Fidelity) will then issue the Form 1099-R by February of 2027 to report the 2026 voluntary after-tax conversion.
COMPLIANCE NOTE:
Conversions are reported in the year that the funds are actually moved over to the Roth account.
The solo 401k contribution rules are different from the conversion rules. Contributions can be made by your business tax return due date plus any timely filed extension for the prior year.
In sum, the voluntary after-tax solo 401k conversion will be nontaxable regardless if you convert the after-tax contributions that were made in 2025 or in 2026 for 2025.
