Good morning. Quick question. Can I make my max contribution ($7000 – I am 55) to my existing IRA, then transfer the new balance to the solo 401k, and then still do my max voluntary contribution for 2020?
While Traditional IRA contributions don't affect the participant's ability to make solo 401k contributions, contributing to a solo 401k plan does affect the ability to make Traditional IRA contributions on a pretax basis (tax deductible).
You can view the IRA contribution limits HERE to determine if the IRA contribution is tax deductible. If it is not tax deductible, and while you can then make it on a non-deductible basis, you won't be able to transfer the non-deductible IRA basis to the solo 401k plan because the IRA rules do not allow for the transfer of non-deductible (after-tax) IRAs to a solo 401k plan.