Yes, our solo 401k plan already allows for annual contributions to be made on a voluntary after-tax basis in addition to allowing for Roth and pre tax contributions. The solo 401k plan documents specify that these contributions can be made.
To put the voluntary after-tax solo 401k to work, you need to open a separate brokerage account under the solo 401k to hold this source of contribution if you have not already done so. By opening a separate brokerage account under the solo 401k to hold voluntary after-tax contributions, this does not result in opening an additional solo 401k.
See below for examples of the different sources allowed in the solo 401k plan below for a plan with one as well as two participants.
After you make the voluntary after-tax solo 401k contribution, you can then convert those funds to the Roth solo 401k or to a Roth IRA. Once in the Roth account, the funds will grow tax free.
After processing the conversion (aka mega backdoor Roth), make sure to complete our on-line conversion form so that we can issue the Form 1099-R to report the non-taxable conversion to the IRS.
