A Roth conversion inside a Solo 401(k), formally called an in-plan Roth rollover, moves value from the pre-tax sub-account of your plan to the Roth sub-account. The converted amount becomes taxable income in the year of conversion, then all future growth and qualified distributions from the Roth account are tax-free. You can convert cash or assets in-kind.
The conversion must be completed by December 31 to apply to the current tax year. If you convert early in the year, estimated quarterly tax payments may be required at the federal and state level. Work with your tax advisor to plan the timing and tax impact before proceeding.
Cash conversions are straightforward, the amount converted is the dollar value moved. If you are converting a non-cash asset, it must be independently valued before the conversion can be recorded. Acceptable valuation methods depend on the asset type:
It is generally cleanest to convert an asset in its entirety. Partial conversions of non-cash assets require a proportional valuation and more complex recordkeeping.
Transfer cash from your pre-tax plan bank account to your Roth plan bank account. For non-cash assets, no re-titling is required; plan assets are always held in the plan name with no reference to the participant sub-account. The conversion is reflected in your internal recordkeeping only.
Complete the Rollover Certification form included in your Self-Directed Plans Solo 401(k) documents. Record the date, the fair market value of the converted amount, and the tax character of the funds. Retain this form and any supporting valuation documentation with your plan records.
As plan administrator, you issue Form 1099-R to yourself reporting the conversion. The form is filed with the IRS and a copy is retained for your records. Complete the form as follows:
Box 1 — Gross distribution: The total amount converted, at fair market value.
Box 2a — Taxable amount: The portion of the conversion that was not previously taxed. This includes all pre-tax contributions, all employer profit-sharing contributions, and all earnings on both pre-tax and after-tax contributions. It does not include any after-tax (non-Roth) contributions you made as those were already taxed when contributed and are not taxed again.
Box 5 — Employee contributions / basis: The after-tax (non-Roth) contribution amount included in the conversion, if any. This represents the portion of Box 1 that is not taxable, and reduces the taxable amount accordingly.
Box 7 — Distribution code: Code G (direct rollover to a qualified plan).
IRA/SEP/SIMPLE checkbox: Leave unchecked. This is a 401(k) plan, not an IRA.
The taxable amount from Box 2a flows to your personal tax return as ordinary income for the year of conversion. Work with your tax advisor or CPA for filing and any estimated tax obligations.
Can I convert just a portion of my pre-tax balance?
Yes. You can convert any amount, from a few dollars to the entire pre-tax balance.
Does a Roth conversion affect the 5-year rule?
Yes. Funds converted to Roth status in your Solo 401(k) must season for five years before qualified distributions can be taken tax-free. The five-year clock starts on January 1 of the tax year in which the conversion occurs.
What if I have both pre-tax and after-tax contributions in my plan?
The taxable portion of the conversion is calculated based on the composition of the converted funds. After-tax contributions already taxed when made are not taxed again. They appear in Box 5 of Form 1099-R and reduce the taxable amount in Box 2a. Your plan contribution records are essential for tracking this correctly.
Can I undo a Roth conversion if I change my mind?
No. Unlike a Roth IRA conversion, in-plan Roth rollovers in a 401(k) cannot be recharacterized. The conversion is permanent. Confirm the tax impact with your advisor before proceeding.
This information is provided for educational purposes only and should not be interpreted as tax, legal, or investment advice. Readers are encouraged to consult a qualified professional who can offer guidance based on their personal situation.