Contribute to Solo 401k from multiple companies

I want to be able to contribute to my Solo 401k from multiple companies to maximize the contribution potential. How can I do this?

Contributions to your Solo 401k can only be made from the adopting business of the plan. Check your plan documents for which adopting business is listed.

If you have multiple companies, you will want to choose the company that generates the most income to be the adopting business of the plan. Or, you may want to consult with your CPA on structuring your companies with a holding company:

• Set up a holding company for the separate companies, and
• Make that holding company the adopting business of the Solo 401k

Holding company

• The holding company is established to own the other companies
• It does not do business itself

Subsidiary companies

• The holding company owns the other companies, which are subsidiary companies
• The subsidiary companies conduct business
• These are pass-through entities (i.e. they don't pay taxation at their own level, the earning is passed through to the parent/holding company)
• If the subsidiary companies are single-member LLCs, for example, then the member would be the parent/holding company. 

Your Solo 401k will need to list the holding company as the adopting business of the plan, which may require an amendment if your plan was already established with a different adopting business.